Compiler/lexical analyzer: Difference between revisions

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Line 3,352: Line 3,352:
Token char_lit(int line, int pos) {
Token char_lit(int line, int pos) {
char c = getNextChar(); // skip opening quote
char c = getNextChar(); // skip opening quote
int n = (int)c;
int n = 0;
if (c == '\'') {
if (c == '\'') {
error(line, pos, "empty character constant");
error(line, pos, "empty character constant");
Line 3,407: Line 3,407:
String text = "";
String text = "";
while (Character.isAlphabetic(this.chr) || Character.isDigit(this.chr) || this.chr == '_') {
while (Character.isAlphabetic(this.chr) || Character.isDigit(this.chr)) {
text += this.chr;
text += this.chr;
if (!Character.isDigit(this.chr)) {
if (!Character.isDigit(this.chr)) {

Revision as of 23:25, 27 March 2019

Task
Compiler/lexical analyzer
You are encouraged to solve this task according to the task description, using any language you may know.

Lexical Analyzer

Definition from Wikipedia:

Lexical analysis is the process of converting a sequence of characters (such as in a computer program or web page) into a sequence of tokens (strings with an identified "meaning"). A program that performs lexical analysis may be called a lexer, tokenizer, or scanner (though "scanner" is also used to refer to the first stage of a lexer).

Create a lexical analyzer for the simple programming language specified below. The program should read input from a file and/or stdin, and write output to a file and/or stdout. If the language being used has a lexer module/library/class, it would be great if two versions of the solution are provided: One without the lexer module, and one with.

Input Specification

The simple programming language to be analyzed is more or less a subset of C. It supports the following tokens:

Operators
Name Common name Character sequence
Op_multiply multiply *
Op_divide divide /
Op_mod mod %
Op_add plus +
Op_subtract minus -
Op_negate unary minus -
Op_less less than <
Op_lessequal less than or equal <=
Op_greater greater than >
Op_greaterequal greater than or equal >=
Op_equal equal ==
Op_notequal not equal !=
Op_not unary not !
Op_assign assignment =
Op_and logical and &&
Op_or logical or ¦¦
  • The - token should always be interpreted as Op_subtract by the lexer. Turning some Op_subtract into Op_negate will be the job of the syntax analyzer, which is not part of this task.
Symbols
Name Common name Character
LeftParen left parenthesis (
RightParen right parenthesis )
LeftBrace left brace {
RightBrace right brace }
Semicolon semi-colon ;
Comma comma ,
Keywords
Name Character sequence
Keyword_if if
Keyword_else else
Keyword_while while
Keyword_print print
Keyword_putc putc
Identifiers and literals

These differ from the the previous tokens, in that each occurrence of them has a value associated with it.

Name Common name Format description Format regex Value
Identifier identifier one or more letter/number/underscore characters, but not starting with a number [_a-zA-Z][_a-zA-Z0-9]* as is
Integer integer literal one or more digits [0-9]+ as is, interpreted as a number
Integer char literal exactly one character (anything except newline or single quote) or one of the allowed escape sequences, enclosed by single quotes '([^'\n]|\\n|\\\\)' the ASCII code point number of the character, e.g. 65 for 'A' and 10 for '\n'
String string literal zero or more characters (anything except newline or double quote), enclosed by double quotes "[^"\n]*" the characters without the double quotes and with escape sequences converted
  • For char and string literals, the \n escape sequence is supported to represent a new-line character.
  • For char and string literals, to represent a backslash, use \\.
  • No other special sequences are supported. This means that:
    • Char literals cannot represent a single quote character (value 39).
    • String literals cannot represent strings containing double quote characters.
Zero-width tokens
Name Location
End_of_input when the end of the input stream is reached
White space
  • Zero or more whitespace characters, or comments enclosed in /* ... */, are allowed between any two tokens, with the exceptions noted below.
  • "Longest token matching" is used to resolve conflicts (e.g., in order to match <= as a single token rather than the two tokens < and =).
  • Whitespace is required between two tokens that have an alphanumeric character or underscore at the edge.
    • This means: keywords, identifiers, and integer literals.
    • e.g. ifprint is recognized as an identifier, instead of the keywords if and print.
    • e.g. 42fred is invalid, and neither recognized as a number nor an identifier.
  • Whitespace is not allowed inside of tokens (except for chars and strings where they are part of the value).
    • e.g. & & is invalid, and not interpreted as the && operator.

For example, the following two program fragments are equivalent, and should produce the same token stream except for the line and column positions:

  • <lang c>if ( p /* meaning n is prime */ ) {
   print ( n , " " ) ;
   count = count + 1 ; /* number of primes found so far */

}</lang>

  • <lang c>if(p){print(n," ");count=count+1;}</lang>
Complete list of token names
End_of_input  Op_multiply   Op_divide     Op_mod       Op_add     Op_subtract
Op_negate     Op_not        Op_less       Op_lessequal Op_greater Op_greaterequal
Op_equal      Op_notequal   Op_assign     Op_and       Op_or      Keyword_if
Keyword_else  Keyword_while Keyword_print Keyword_putc LeftParen  RightParen
LeftBrace     RightBrace    Semicolon     Comma        Identifier Integer
String
Output Format

The program output should be a sequence of lines, each consisting of the following whitespace-separated fields:

  1. the line number where the token starts
  2. the column number where the token starts
  3. the token name
  4. the token value (only for Identifier, Integer, and String tokens)
  5. the number of spaces between fields is up to you. Neatly aligned is nice, but not a requirement.
Diagnostics

The following error conditions should be caught:

Error Example
Empty character constant ''
Unknown escape sequence. \r
Multi-character constant. 'xx'
End-of-file in comment. Closing comment characters not found.
End-of-file while scanning string literal. Closing string character not found.
End-of-line while scanning string literal. Closing string character not found before end-of-line.
Unrecognized character.
Invalid number. Starts like a number, but ends in non-numeric characters. 123abc
Test Cases
Input Output

Test Case 1: <lang c>/*

 Hello world
*/

print("Hello, World!\n");</lang>

    4      1 Keyword_print
    4      6 LeftParen
    4      7 String         "Hello, World!\n"
    4     24 RightParen
    4     25 Semicolon
    5      1 End_of_input

Test Case 2: <lang c>/*

 Show Ident and Integers
*/

phoenix_number = 142857; print(phoenix_number, "\n");</lang>

    4      1 Identifier     phoenix_number
    4     16 Op_assign
    4     18 Integer         142857
    4     24 Semicolon
    5      1 Keyword_print
    5      6 LeftParen
    5      7 Identifier     phoenix_number
    5     21 Comma
    5     23 String         "\n"
    5     27 RightParen
    5     28 Semicolon
    6      1 End_of_input

Test Case 3: <lang c>/*

 All lexical tokens - not syntactically correct, but that will
 have to wait until syntax analysis
*/

/* Print */ print /* Sub */ - /* Putc */ putc /* Lss */ < /* If */ if /* Gtr */ > /* Else */ else /* Leq */ <= /* While */ while /* Geq */ >= /* Lbrace */ { /* Eq */ == /* Rbrace */ } /* Neq */  != /* Lparen */ ( /* And */ && /* Rparen */ ) /* Or */ || /* Uminus */ - /* Semi */  ; /* Not */  ! /* Comma */ , /* Mul */ * /* Assign */ = /* Div */ / /* Integer */ 42 /* Mod */  % /* String */ "String literal" /* Add */ + /* Ident */ variable_name /* character literal */ '\n' /* character literal */ '\\' /* character literal */ ' '</lang>

    5     16   Keyword_print
    5     40   Op_subtract
    6     16   Keyword_putc
    6     40   Op_less
    7     16   Keyword_if
    7     40   Op_greater
    8     16   Keyword_else
    8     40   Op_lessequal
    9     16   Keyword_while
    9     40   Op_greaterequal
   10     16   LeftBrace
   10     40   Op_equal
   11     16   RightBrace
   11     40   Op_notequal
   12     16   LeftParen
   12     40   Op_and
   13     16   RightParen
   13     40   Op_or
   14     16   Op_subtract
   14     40   Semicolon
   15     16   Op_not
   15     40   Comma
   16     16   Op_multiply
   16     40   Op_assign
   17     16   Op_divide
   17     40   Integer             42
   18     16   Op_mod
   18     40   String          "String literal"
   19     16   Op_add
   19     40   Identifier      variable_name
   20     26   Integer             10
   21     26   Integer             92
   22     26   Integer             32
   23      1   End_of_input

Test Case 4: <lang c>/*** test printing, embedded \n and comments with lots of '*' ***/ print(42); print("\nHello World\nGood Bye\nok\n"); print("Print a slash n - \\n.\n");</lang>

    2      1 Keyword_print
    2      6 LeftParen
    2      7 Integer            42
    2      9 RightParen
    2     10 Semicolon
    3      1 Keyword_print
    3      6 LeftParen
    3      7 String          "\nHello World\nGood Bye\nok\n"
    3     38 RightParen
    3     39 Semicolon
    4      1 Keyword_print
    4      6 LeftParen
    4      7 String          "Print a slash n - \\n.\n"
    4     33 RightParen
    4     34 Semicolon
    5      1 End_of_input
Additional examples

Your solution should pass all the test cases above and the additional tests found Here.

Reference

The C and Python versions can be considered reference implementations.

Related Tasks

ALGOL W

<lang algolw>begin

   %lexical analyser %
   % Algol W strings are limited to 256 characters in length so we limit source lines %
   % and tokens to 256 characters %
   integer     lineNumber, columnNumber;
   string(256) line;
   string(256) tkValue;
   integer     tkType, tkLine, tkColumn, tkLength, tkIntegerValue;
   logical     tkTooLong;
   string(1)   currChar;
   string(1)   newlineChar;
   integer     LINE_WIDTH, MAX_TOKEN_LENGTH, MAXINTEGER_OVER_10, MAXINTEGER_MOD_10;
   integer     tOp_multiply   , tOp_divide        , tOp_mod       , tOp_add
         ,     tOp_subtract   , tOp_negate        , tOp_less      , tOp_lessequal
         ,     tOp_greater    , tOp_greaterequal  , tOp_equal     , tOp_notequal
         ,     tOp_not        , tOp_assign        , tOp_and       , tOp_or
         ,     tLeftParen     , tRightParen       , tLeftBrace    , tRightBrace
         ,     tSemicolon     , tComma            , tKeyword_if   , tKeyword_else
         ,     tKeyword_while , tKeyword_print    , tKeyword_putc , tIdentifier
         ,     tInteger       , tString           , tEnd_of_input , tComment
         ;
   string(16)  array tkName ( 1 :: 32 );
   % reports an error %
   procedure lexError( string(80) value message ); begin
       integer errorPos;
       write( i_w := 1, s_w := 0, "**** Error at(", lineNumber, ",", columnNumber, "): " );
       errorPos := 0;
       while errorPos < 80 and message( errorPos // 1 ) not = "." do begin
           writeon( s_w := 0, message( errorPos // 1 ) );
           errorPos := errorPos + 1
       end while_not_at_end_of_message ;
       writeon( s_w := 0, "." )
   end lexError ;
   % gets the next source character %
   procedure nextChar ; begin
       if      columnNumber = LINE_WIDTH then begin
           currChar     := newlineChar;
           columnNumber := columnNumber + 1
           end
       else if columnNumber > LINE_WIDTH then begin
           readcard( line );
           columnNumber := 1;
           if not XCPNOTED(ENDFILE) then lineNumber := lineNumber + 1;
           currChar     := line( 0 // 1 )
           end
       else begin
           currChar     := line( columnNumber // 1 );
           columnNumber := columnNumber + 1
       end
   end nextChar ;
   % gets the next token, returns the token type %
   integer procedure nextToken ; begin
       % returns true if currChar is in the inclusive range lowerValue to upperValue %
       %         false otherwise %
       logical procedure range( string(1) value lowerValue, upperValue ) ; begin
           currChar >= lowerValue and currChar <= upperValue
       end range ;
       % returns true if the current character can start an identifier, false otherwise %
       logical procedure identifierStartChar ; begin
           currChar = "_" or range( "a", "z" ) or range( "A", "Z" )
       end identifierStartChar ;
       % add the current character to the token and get the next %
       procedure addAndNextChar ; begin
           if tkLength >= MAX_TOKEN_LENGTH then tkTooLong := true
           else begin
               tkValue( tkLength // 1 ) := currChar;
               tkLength                 := tkLength + 1
           end if_symbol_not_too_long ;
           nextChar
       end % addAndNextChar % ;
       % handle a single character token %
       procedure singleCharToken( integer value tokenType ) ; begin
           tkType := tokenType;
           nextChar
       end singleCharToken ;
       % handle a doubled character token: && or || %
       procedure doubleCharToken( integer value tokenType ) ; begin
           string(1) firstChar;
           firstChar := currChar;
           tkType    := tokenType;
           nextChar;
           if currChar = firstChar then nextChar
           else % the character wasn't doubled % lexError( "Unrecognised character." );
       end singleCharToken ;
       % handle an operator or operator= token %
       procedure opOrOpEqual( integer value opToken, opEqualToken ) ; begin
           tkType := opToken;
           nextChar;
           if currChar = "=" then begin
               % have operator= %
               tkType := opEqualToken;
               nextChar
           end if_currChar_is_equal ;
       end opOrOpEqual ;
       % handle a / operator or /* comment %
       procedure divideOrComment ; begin
           tkType := tOp_divide;
           nextChar;
           if currChar = "*" then begin
               % have a comment %
               logical moreComment;
               tkType      := tComment;
               moreComment := true;
               while moreComment do begin
                   nextChar;
                   while currChar not = "*" and not XCPNOTED(ENDFILE) do nextChar;
                   while currChar     = "*" and not XCPNOTED(ENDFILE) do nextChar;
                   moreComment := ( currChar not = "/" and not XCPNOTED(ENDFILE) )
               end while_more_comment ;
               if not XCPNOTED(ENDFILE)
               then nextChar
               else lexError( "End-of-file in comment." )
           end if_currChar_is_star ;
       end divideOrComment ;
       % handle an indentifier or keyword %
       procedure identifierOrKeyword ; begin
           tkType := tIdentifier;
           while identifierStartChar or range( "0", "9" ) do addAndNextChar;
           % there are only 5 keywords, so we just test each in turn here %
           if      tkValue = "if"      then tkType  := tKeyword_if
           else if tkValue = "else"    then tkType  := tKeyword_else
           else if tkValue = "while"   then tkType  := tKeyword_while
           else if tkValue = "print"   then tkType  := tKeyword_print
           else if tkValue = "putc"    then tkType  := tKeyword_putc;
           if tkType not = tIdentifier then tkValue := "";
       end identifierOrKeyword ;
       % handle an integer literal %
       procedure integerLiteral ; begin
           logical overflowed;
           integer digit;
           overflowed := false;
           tkType     := tInteger;
           while range( "0", "9" ) do begin
               digit := ( decode( currChar ) - decode( "0" ) );
               if      tkIntegerValue > MAXINTEGER_OVER_10 then overflowed := true
               else if tkIntegerValue = MAXINTEGER_OVER_10
                   and digit          > MAXINTEGER_MOD_10  then overflowed := true
               else begin
                   tkIntegerValue := tkIntegerValue * 10;
                   tkIntegerValue := tkIntegerValue + digit;
               end;
               nextChar
           end while_have_a_digit ;
           if overflowed          then lexError( "Number too large." );
           if identifierStartChar then lexError( "Number followed by letter or underscore." );
       end integerLiteral ;
       % handle a char literal %
       procedure charLiteral ; begin
           nextChar;
           if      currChar = "'" or currChar = newlineChar then lexError( "Invalid character constant." )
           else if currChar = "\" then begin
               % have an escape %
               nextChar;
               if      currChar     = "n" then currChar := newlineChar
               else if currChar not = "\" then lexError( "Unknown escape sequence." )
           end;
           tkType         := tInteger;
           tkIntegerValue := decode( currChar );
           % should have a closing quoute next %
           nextChar;
           if   currChar not = "'"
           then lexError( "Multi-character constant." )
           else nextChar
       end charLiteral ;
       % handle a string literal %
       procedure stringLiteral ; begin
           tkType            := tString;
           tkValue( 0 // 1 ) := currChar;
           tkLength          := 1;
           nextChar;
           while currChar not = """" and currChar not = newlineChar and not XCPNOTED(ENDFILE) do addAndNextChar;
           if      currChar = newlineChar then lexError( "End-of-line while scanning string literal." )
           else if XCPNOTED(ENDFILE)      then lexError( "End-of-file while scanning string literal." )
           else    % currChar must be """" % addAndNextChar
       end stringLiteral ;
       while begin
           % skip white space %
           while ( currChar = " " or currChar = newlineChar ) and not XCPNOTED(ENDFILE) do nextChar;
           % get the token %
           tkLine         := lineNumber;
           tkColumn       := columnNumber;
           tkValue        := "";
           tkLength       := 0;
           tkIntegerValue := 0;
           tkTooLong      := false;
           if      XCPNOTED(ENDFILE)   then tkType := tEnd_of_input
           else if currChar = "*"      then singleCharToken( tOp_multiply )
           else if currChar = "/"      then divideOrComment
           else if currChar = "%"      then singleCharToken( tOp_mod      )
           else if currChar = "+"      then singleCharToken( tOp_add )
           else if currChar = "-"      then singleCharToken( tOp_subtract )
           else if currChar = "<"      then opOrOpEqual( tOp_less,    tOp_lessequal     )
           else if currChar = ">"      then opOrOpEqual( tOp_greater, tOp_greaterequal  )
           else if currChar = "="      then opOrOpEqual( tOp_assign,  tOp_equal         )
           else if currChar = "!"      then opOrOpEqual( tOp_not,     tOp_notequal      )
           else if currChar = "&"      then doubleCharToken( tOp_and     )
           else if currChar = "|"      then doubleCharToken( tOp_or      )
           else if currChar = "("      then singleCharToken( tLeftParen  )
           else if currChar = ")"      then singleCharToken( tRightParen )
           else if currChar = "{"      then singleCharToken( tLeftBrace  )
           else if currChar = "}"      then singleCharToken( tRightBrace )
           else if currChar = ";"      then singleCharToken( tSemicolon  )
           else if currChar = ","      then singleCharToken( tComma      )
           else if identifierStartChar then identifierOrKeyword
           else if range( "0", "9" )   then integerLiteral
           else if currChar = "'"      then charLiteral
           else if currChar = """"     then stringLiteral
           else begin
               lexError( "Unrecognised character." );
               singleCharToken( tComment )
           end ;
           % continue until we get something other than a comment %
           tkType = tComment
       end do begin end;
       if tkTooLong then if   tkType = tString
                         then lexError( "String literal too long." )
                         else lexError( "Identifier too long."     );
       tkType
   end nextToken ;
   % outputs the current token %
   procedure writeToken ; begin
       write( i_w := 5, s_w := 2, tkLine, tkColumn, tkName( tkType ) );
       if tkType = tInteger then writeon( i_w := 11, tkIntegerValue )
       else if tkLength > 0 then begin
           writeon( "  " );
           for tkPos := 0 until tkLength - 1 do writeon( s_w := 0, tkValue( tkPos // 1 ) );
       end
   end writeToken ;
   LINE_WIDTH       := 256; MAXINTEGER_MOD_10  := MAXINTEGER rem 10;
   MAX_TOKEN_LENGTH := 256; MAXINTEGER_OVER_10 := MAXINTEGER div 10;
   newlineChar      := code( 10 );
   tOp_multiply     :=  1; tkName( tOp_multiply     ) := "Op_multiply";
   tOp_divide       :=  2; tkName( tOp_divide       ) := "Op_divide";
   tOp_mod          :=  3; tkName( tOp_mod          ) := "Op_mod";
   tOp_add          :=  4; tkName( tOp_add          ) := "Op_add";
   tOp_subtract     :=  5; tkName( tOp_subtract     ) := "Op_subtract";
   tOp_negate       :=  6; tkName( tOp_negate       ) := "Op_negate";
   tOp_less         :=  7; tkName( tOp_less         ) := "Op_less";
   tOp_lessequal    :=  8; tkName( tOp_lessequal    ) := "Op_lessequal";
   tOp_greater      :=  9; tkName( tOp_greater      ) := "Op_greater";
   tOp_greaterequal := 10; tkName( tOp_greaterequal ) := "Op_greaterequal";
   tOp_equal        := 11; tkName( tOp_equal        ) := "Op_equal";
   tOp_notequal     := 12; tkName( tOp_notequal     ) := "Op_notequal";
   tOp_not          := 13; tkName( tOp_not          ) := "Op_not";
   tOp_assign       := 14; tkName( tOp_assign       ) := "Op_assign";
   tOp_and          := 15; tkName( tOp_and          ) := "Op_and";
   tOp_or           := 16; tkName( tOp_or           ) := "Op_or";
   tLeftParen       := 17; tkName( tLeftParen       ) := "LeftParen";
   tRightParen      := 18; tkName( tRightParen      ) := "RightParen";
   tLeftBrace       := 19; tkName( tLeftBrace       ) := "LeftBrace";
   tRightBrace      := 20; tkName( tRightBrace      ) := "RightBrace";
   tSemicolon       := 21; tkName( tSemicolon       ) := "Semicolon";
   tComma           := 22; tkName( tComma           ) := "Comma";
   tKeyword_if      := 23; tkName( tKeyword_if      ) := "Keyword_if";
   tKeyword_else    := 24; tkName( tKeyword_else    ) := "Keyword_else";
   tKeyword_while   := 25; tkName( tKeyword_while   ) := "Keyword_while";
   tKeyword_print   := 26; tkName( tKeyword_print   ) := "Keyword_print";
   tKeyword_putc    := 27; tkName( tKeyword_putc    ) := "Keyword_putc";
   tIdentifier      := 28; tkName( tIdentifier      ) := "Identifier";
   tInteger         := 29; tkName( tInteger         ) := "Integer";
   tString          := 30; tkName( tString          ) := "String";
   tEnd_of_input    := 31; tkName( tEnd_of_input    ) := "End_of_input";
   tComment         := 32; tkName( tComment         ) := "Comment";
   % allow the program to continue after reaching end-of-file %
   ENDFILE := EXCEPTION( false, 1, 0, false, "EOF" );
   % ensure the first call to nextToken reads the first line %
   lineNumber   := 0;
   columnNumber := LINE_WIDTH + 1;
   currChar     := " ";
   % get and print all tokens from standard input %
   while nextToken not = tEnd_of_input do writeToken;
   writeToken

end.</lang>

Output:

Test case 3

    5     16  Keyword_print            
    5     40  Op_subtract     
    6     16  Keyword_putc            
    6     40  Op_less         
    7     16  Keyword_if            
    7     40  Op_greater      
    8     16  Keyword_else            
    8     40  Op_lessequal    
    9     16  Keyword_while            
    9     40  Op_greaterequal 
   10     16  LeftBrace       
   10     40  Op_equal        
   11     16  RightBrace      
   11     40  Op_notequal     
   12     16  LeftParen       
   12     40  Op_and          
   13     16  RightParen      
   13     40  Op_or           
   14     16  Op_subtract     
   14     40  Semicolon       
   15     16  Op_not          
   15     40  Comma           
   16     16  Op_multiply     
   16     40  Op_assign       
   17     16  Op_divide       
   17     40  Integer                  42  
   18     16  Op_mod          
   18     40  String              "String literal"
   19     16  Op_add          
   19     40  Identifier          variable_name
   20     26  Integer                  10  
   21     26  Integer                  92  
   22     26  Integer                  32  
   23      1  End_of_input    

AWK

Tested with gawk 4.1.1 and mawk 1.3.4. <lang AWK> BEGIN {

 all_syms["tk_EOI"    ] = "End_of_input"
 all_syms["tk_Mul"    ] = "Op_multiply"
 all_syms["tk_Div"    ] = "Op_divide"
 all_syms["tk_Mod"    ] = "Op_mod"
 all_syms["tk_Add"    ] = "Op_add"
 all_syms["tk_Sub"    ] = "Op_subtract"
 all_syms["tk_Negate" ] = "Op_negate"
 all_syms["tk_Not"    ] = "Op_not"
 all_syms["tk_Lss"    ] = "Op_less"
 all_syms["tk_Leq"    ] = "Op_lessequal"
 all_syms["tk_Gtr"    ] = "Op_greater"
 all_syms["tk_Geq"    ] = "Op_greaterequal"
 all_syms["tk_Eq"     ] = "Op_equal"
 all_syms["tk_Neq"    ] = "Op_notequal"
 all_syms["tk_Assign" ] = "Op_assign"
 all_syms["tk_And"    ] = "Op_and"
 all_syms["tk_Or"     ] = "Op_or"
 all_syms["tk_If"     ] = "Keyword_if"
 all_syms["tk_Else"   ] = "Keyword_else"
 all_syms["tk_While"  ] = "Keyword_while"
 all_syms["tk_Print"  ] = "Keyword_print"
 all_syms["tk_Putc"   ] = "Keyword_putc"
 all_syms["tk_Lparen" ] = "LeftParen"
 all_syms["tk_Rparen" ] = "RightParen"
 all_syms["tk_Lbrace" ] = "LeftBrace"
 all_syms["tk_Rbrace" ] = "RightBrace"
 all_syms["tk_Semi"   ] = "Semicolon"
 all_syms["tk_Comma"  ] = "Comma"
 all_syms["tk_Ident"  ] = "Identifier"
 all_syms["tk_Integer"] = "Integer"
 all_syms["tk_String" ] = "String"
 ## single character only symbols
 symbols["{"   ] = "tk_Lbrace"
 symbols["}"   ] = "tk_Rbrace"
 symbols["("   ] = "tk_Lparen"
 symbols[")"   ] = "tk_Rparen"
 symbols["+"   ] = "tk_Add"
 symbols["-"   ] = "tk_Sub"
 symbols["*"   ] = "tk_Mul"
 symbols["%"   ] = "tk_Mod"
 symbols[";"   ] = "tk_Semi"
 symbols[","   ] = "tk_Comma"
 key_words["if"   ] = "tk_If"
 key_words["else" ] = "tk_Else"
 key_words["print"] = "tk_Print"
 key_words["putc" ] = "tk_Putc"
 key_words["while"] = "tk_While"
 # Set up an array that emulates the ord() function.
 for(n=0;n<256;n++)
   ord[sprintf("%c",n)]=n
 input_file = "-"
 if (ARGC > 1)
   input_file = ARGV[1]
 RS=FS=""   # read complete file into one line $0
 getline < input_file
 the_ch = " " # dummy first char - but it must be a space
 the_col  = 0 # always points to the current character
 the_line = 1
 for (the_nf=1; ; ) {
   split(gettok(), t, SUBSEP)
   printf("%5s  %5s %-14s", t[2], t[3], all_syms[t[1]])
   if      (t[1] == "tk_Integer") printf("   %5s\n", t[4])
   else if (t[1] == "tk_Ident"  ) printf("  %s\n",   t[4])
   else if (t[1] == "tk_String" ) printf("  \"%s\"\n", t[4])
   else                           print("")
   if (t[1] == "tk_EOI")
     break
 }

}

        • show error and exit

function error(line, col, msg) {

 print(line, col, msg)
 exit(1)

}

  1. get the next character from the input

function next_ch() {

 the_ch = $the_nf
 the_nf  ++
 the_col ++
 if (the_ch == "\n") {
   the_line ++
   the_col = 0
 }
 return the_ch

}

        • 'x' - character constants

function char_lit(err_line, err_col) {

 n = ord[next_ch()]              # skip opening quote
 if (the_ch == "'") {
   error(err_line, err_col, "empty character constant")
 } else if (the_ch == "\\") {
   next_ch()
   if (the_ch == "n")
     n = 10
   else if (the_ch == "\\")
     n = ord["\\"]
   else
     error(err_line, err_col, "unknown escape sequence " the_ch)
 }
 if (next_ch() != "'")
   error(err_line, err_col, "multi-character constant")
 next_ch()
 return "tk_Integer" SUBSEP err_line SUBSEP err_col SUBSEP n

}

        • process divide or comments

function div_or_cmt(err_line, err_col) {

 if (next_ch() != "*")
   return "tk_Div" SUBSEP err_line SUBSEP err_col
 # comment found
 next_ch()
 while (1) {
   if (the_ch == "*") {
     if (next_ch() == "/") {
       next_ch()
       return gettok()
     } else if (the_ch == "") {
       error(err_line, err_col, "EOF in comment")
     }
   } else {
     next_ch()
   }
 }

}

        • "string"

function string_lit(start, err_line, err_col) {

 text = ""
 while (next_ch() != start) {
   if (the_ch == "")
     error(err_line, err_col, "EOF while scanning string literal")
   if (the_ch == "\n")
     error(err_line, err_col, "EOL while scanning string literal")
   text = text the_ch
 }
 next_ch()
 return "tk_String" SUBSEP err_line SUBSEP err_col SUBSEP text

}

        • handle identifiers and integers

function ident_or_int(err_line, err_col) {

 is_number = 1
 text = ""
 while ((the_ch ~ /^[0-9a-zA-Z]+$/)  || (the_ch == "_")) {
   text = text the_ch
   if (! (the_ch ~ /^[0-9]+$/))
     is_number = 0
   next_ch()
 }
 if (text == "")
   error(err_line, err_col, "ident_or_int: unrecognized character: " the_ch)
 if (text ~ /^[0-9]/) {
   if (! is_number)
     error(err_line, err_col, "invalid number: " text)
   n = text + 0
   return "tk_Integer" SUBSEP err_line SUBSEP err_col SUBSEP n
 }
 if (text in key_words)
   return key_words[text] SUBSEP err_line SUBSEP err_col
 return "tk_Ident" SUBSEP err_line SUBSEP err_col SUBSEP text

}

        • look ahead for '>=', etc.

function follow(expect, ifyes, ifno, err_line, err_col) {

 if (next_ch() == expect) {
   next_ch()
   return ifyes SUBSEP err_line SUBSEP err_col
 }
 if (ifno == tk_EOI)
   error(err_line, err_col, "follow: unrecognized character: " the_ch)
 return ifno SUBSEP err_line SUBSEP err_col

}

        • return the next token type

function gettok() {

 while (the_ch == " " || the_ch == "\n" || the_ch == "\r")
   next_ch()
 err_line = the_line
 err_col  = the_col
 if      (the_ch == "" )    return "tk_EOI" SUBSEP err_line SUBSEP err_col
 else if (the_ch == "/")    return div_or_cmt(err_line, err_col)
 else if (the_ch == "'")    return char_lit(err_line, err_col)
 else if (the_ch == "<")    return follow("=", "tk_Leq", "tk_Lss",    err_line, err_col)
 else if (the_ch == ">")    return follow("=", "tk_Geq", "tk_Gtr",    err_line, err_col)
 else if (the_ch == "=")    return follow("=", "tk_Eq",  "tk_Assign", err_line, err_col)
 else if (the_ch == "!")    return follow("=", "tk_Neq", "tk_Not",    err_line, err_col)
 else if (the_ch == "&")    return follow("&", "tk_And", "tk_EOI",    err_line, err_col)
 else if (the_ch == "|")    return follow("|", "tk_Or",  "tk_EOI",    err_line, err_col)
 else if (the_ch =="\"")    return string_lit(the_ch, err_line, err_col)
 else if (the_ch in symbols) {
   sym = symbols[the_ch]
   next_ch()
   return sym SUBSEP err_line SUBSEP err_col
 } else {
   return ident_or_int(err_line, err_col)
 }

} </lang>

Output  —  count:

    1      1 Identifier      count
    1      7 Op_assign     
    1      9 Integer              1
    1     10 Semicolon     
    2      1 Keyword_while 
    2      7 LeftParen     
    2      8 Identifier      count
    2     14 Op_less       
    2     16 Integer             10
    2     18 RightParen    
    2     20 LeftBrace     
    3      5 Keyword_print 
    3     10 LeftParen     
    3     11 String          "count is: "
    3     23 Comma         
    3     25 Identifier      count
    3     30 Comma         
    3     32 String          "\n"
    3     36 RightParen    
    3     37 Semicolon     
    4      5 Identifier      count
    4     11 Op_assign     
    4     13 Identifier      count
    4     19 Op_add        
    4     21 Integer              1
    4     22 Semicolon     
    5      1 RightBrace    
    5      3 End_of_input 

C

Tested with gcc 4.81 and later, compiles warning free with -Wall -Wextra <lang C>#include <stdlib.h>

  1. include <stdio.h>
  2. include <stdarg.h>
  3. include <ctype.h>
  4. include <string.h>
  5. include <errno.h>
  6. include <stdbool.h>
  7. include <limits.h>
  1. define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))
  1. define da_dim(name, type) type *name = NULL; \
                           int _qy_ ## name ## _p = 0;  \
                           int _qy_ ## name ## _max = 0
  1. define da_rewind(name) _qy_ ## name ## _p = 0
  2. define da_redim(name) do {if (_qy_ ## name ## _p >= _qy_ ## name ## _max) \
                               name = realloc(name, (_qy_ ## name ## _max += 32) * sizeof(name[0]));} while (0)
  1. define da_append(name, x) do {da_redim(name); name[_qy_ ## name ## _p++] = x;} while (0)
  2. define da_len(name) _qy_ ## name ## _p

typedef enum {

   tk_EOI, tk_Mul, tk_Div, tk_Mod, tk_Add, tk_Sub, tk_Negate, tk_Not, tk_Lss, tk_Leq,
   tk_Gtr, tk_Geq, tk_Eq, tk_Neq, tk_Assign, tk_And, tk_Or, tk_If, tk_Else, tk_While,
   tk_Print, tk_Putc, tk_Lparen, tk_Rparen, tk_Lbrace, tk_Rbrace, tk_Semi, tk_Comma,
   tk_Ident, tk_Integer, tk_String

} TokenType;

typedef struct {

   TokenType tok;
   int err_ln, err_col;
   union {
       int n;                  /* value for constants */
       char *text;             /* text for idents */
   };

} tok_s;

static FILE *source_fp, *dest_fp; static int line = 1, col = 0, the_ch = ' '; da_dim(text, char);

tok_s gettok();

static void error(int err_line, int err_col, const char *fmt, ... ) {

   char buf[1000];
   va_list ap;
   va_start(ap, fmt);
   vsprintf(buf, fmt, ap);
   va_end(ap);
   printf("(%d,%d) error: %s\n", err_line, err_col, buf);
   exit(1);

}

static int next_ch() { /* get next char from input */

   the_ch = getc(source_fp);
   ++col;
   if (the_ch == '\n') {
       ++line;
       col = 0;
   }
   return the_ch;

}

static tok_s char_lit(int n, int err_line, int err_col) { /* 'x' */

   if (the_ch == '\)
       error(err_line, err_col, "gettok: empty character constant");
   if (the_ch == '\\') {
       next_ch();
       if (the_ch == 'n')
           n = 10;
       else if (the_ch == '\\')
           n = '\\';
       else error(err_line, err_col, "gettok: unknown escape sequence \\%c", the_ch);
   }
   if (next_ch() != '\)
       error(err_line, err_col, "multi-character constant");
   next_ch();
   return (tok_s){tk_Integer, err_line, err_col, {n}};

}

static tok_s div_or_cmt(int err_line, int err_col) { /* process divide or comments */

   if (the_ch != '*')
       return (tok_s){tk_Div, err_line, err_col, {0}};
   /* comment found */
   next_ch();
   for (;;) {
       if (the_ch == '*') {
           if (next_ch() == '/') {
               next_ch();
               return gettok();
           }
       } else if (the_ch == EOF)
           error(err_line, err_col, "EOF in comment");
       else
           next_ch();
   }

}

static tok_s string_lit(int start, int err_line, int err_col) { /* "st" */

   da_rewind(text);
   while (next_ch() != start) {
       if (the_ch == '\n') error(err_line, err_col, "EOL in string");
       if (the_ch == EOF)  error(err_line, err_col, "EOF in string");
       da_append(text, (char)the_ch);
   }
   da_append(text, '\0');
   next_ch();
   return (tok_s){tk_String, err_line, err_col, {.text=text}};

}

static int kwd_cmp(const void *p1, const void *p2) {

   return strcmp(*(char **)p1, *(char **)p2);

}

static TokenType get_ident_type(const char *ident) {

   static struct {
       char *s;
       TokenType sym;
   } kwds[] = {
       {"else",  tk_Else},
       {"if",    tk_If},
       {"print", tk_Print},
       {"putc",  tk_Putc},
       {"while", tk_While},
   }, *kwp;
   return (kwp = bsearch(&ident, kwds, NELEMS(kwds), sizeof(kwds[0]), kwd_cmp)) == NULL ? tk_Ident : kwp->sym;

}

static tok_s ident_or_int(int err_line, int err_col) {

   int n, is_number = true;
   da_rewind(text);
   while (isalnum(the_ch) || the_ch == '_') {
       da_append(text, (char)the_ch);
       if (!isdigit(the_ch))
           is_number = false;
       next_ch();
   }
   if (da_len(text) == 0)
       error(err_line, err_col, "gettok: unrecognized character (%d) '%c'\n", the_ch, the_ch);
   da_append(text, '\0');
   if (isdigit(text[0])) {
       if (!is_number)
           error(err_line, err_col, "invalid number: %s\n", text);
       n = strtol(text, NULL, 0);
       if (n == LONG_MAX && errno == ERANGE)
           error(err_line, err_col, "Number exceeds maximum value");
       return (tok_s){tk_Integer, err_line, err_col, {n}};
   }
   return (tok_s){get_ident_type(text), err_line, err_col, {.text=text}};

}

static tok_s follow(int expect, TokenType ifyes, TokenType ifno, int err_line, int err_col) { /* look ahead for '>=', etc. */

   if (the_ch == expect) {
       next_ch();
       return (tok_s){ifyes, err_line, err_col, {0}};
   }
   if (ifno == tk_EOI)
       error(err_line, err_col, "follow: unrecognized character '%c' (%d)\n", the_ch, the_ch);
   return (tok_s){ifno, err_line, err_col, {0}};

}

tok_s gettok() { /* return the token type */

   /* skip white space */
   while (isspace(the_ch))
       next_ch();
   int err_line = line;
   int err_col  = col;
   switch (the_ch) {
       case '{':  next_ch(); return (tok_s){tk_Lbrace, err_line, err_col, {0}};
       case '}':  next_ch(); return (tok_s){tk_Rbrace, err_line, err_col, {0}};
       case '(':  next_ch(); return (tok_s){tk_Lparen, err_line, err_col, {0}};
       case ')':  next_ch(); return (tok_s){tk_Rparen, err_line, err_col, {0}};
       case '+':  next_ch(); return (tok_s){tk_Add, err_line, err_col, {0}};
       case '-':  next_ch(); return (tok_s){tk_Sub, err_line, err_col, {0}};
       case '*':  next_ch(); return (tok_s){tk_Mul, err_line, err_col, {0}};
       case '%':  next_ch(); return (tok_s){tk_Mod, err_line, err_col, {0}};
       case ';':  next_ch(); return (tok_s){tk_Semi, err_line, err_col, {0}};
       case ',':  next_ch(); return (tok_s){tk_Comma,err_line, err_col, {0}};
       case '/':  next_ch(); return div_or_cmt(err_line, err_col);
       case '\: next_ch(); return char_lit(the_ch, err_line, err_col);
       case '<':  next_ch(); return follow('=', tk_Leq, tk_Lss,    err_line, err_col);
       case '>':  next_ch(); return follow('=', tk_Geq, tk_Gtr,    err_line, err_col);
       case '=':  next_ch(); return follow('=', tk_Eq,  tk_Assign, err_line, err_col);
       case '!':  next_ch(); return follow('=', tk_Neq, tk_Not,    err_line, err_col);
       case '&':  next_ch(); return follow('&', tk_And, tk_EOI,    err_line, err_col);
       case '|':  next_ch(); return follow('|', tk_Or,  tk_EOI,    err_line, err_col);
       case '"' : return string_lit(the_ch, err_line, err_col);
       default:   return ident_or_int(err_line, err_col);
       case EOF:  return (tok_s){tk_EOI, err_line, err_col, {0}};
   }

}

void run() { /* tokenize the given input */

   tok_s tok;
   do {
       tok = gettok();
       fprintf(dest_fp, "%5d  %5d %.15s",
           tok.err_ln, tok.err_col,
           &"End_of_input    Op_multiply     Op_divide       Op_mod          Op_add          "
            "Op_subtract     Op_negate       Op_not          Op_less         Op_lessequal    "
            "Op_greater      Op_greaterequal Op_equal        Op_notequal     Op_assign       "
            "Op_and          Op_or           Keyword_if      Keyword_else    Keyword_while   "
            "Keyword_print   Keyword_putc    LeftParen       RightParen      LeftBrace       "
            "RightBrace      Semicolon       Comma           Identifier      Integer         "
            "String          "
           [tok.tok * 16]);
       if (tok.tok == tk_Integer)     fprintf(dest_fp, "  %4d",   tok.n);
       else if (tok.tok == tk_Ident)  fprintf(dest_fp, " %s",     tok.text);
       else if (tok.tok == tk_String) fprintf(dest_fp, " \"%s\"", tok.text);
       fprintf(dest_fp, "\n");
   } while (tok.tok != tk_EOI);
   if (dest_fp != stdout)
       fclose(dest_fp);

}

void init_io(FILE **fp, FILE *std, const char mode[], const char fn[]) {

   if (fn[0] == '\0')
       *fp = std;
   else if ((*fp = fopen(fn, mode)) == NULL)
       error(0, 0, "Can't open %s\n", fn);

}

int main(int argc, char *argv[]) {

   init_io(&source_fp, stdin,  "r",  argc > 1 ? argv[1] : "");
   init_io(&dest_fp,   stdout, "wb", argc > 2 ? argv[2] : "");
   run();
   return 0;

}</lang>

Output  —  test case 3:

    5     16 Keyword_print
    5     40 Op_subtract
    6     16 Keyword_putc
    6     40 Op_less
    7     16 Keyword_if
    7     40 Op_greater
    8     16 Keyword_else
    8     40 Op_lessequal
    9     16 Keyword_while
    9     40 Op_greaterequal
   10     16 LeftBrace
   10     40 Op_equal
   11     16 RightBrace
   11     40 Op_notequal
   12     16 LeftParen
   12     40 Op_and
   13     16 RightParen
   13     40 Op_or
   14     16 Op_subtract
   14     40 Semicolon
   15     16 Op_not
   15     40 Comma
   16     16 Op_multiply
   16     40 Op_assign
   17     16 Op_divide
   17     40 Integer            42
   18     16 Op_mod
   18     40 String          "String literal"
   19     16 Op_add
   19     40 Identifier      variable_name
   20     26 Integer            10
   21     26 Integer            92
   22     26 Integer            32
   23      1 End_of_input

C#

Requires C#6.0 because of the use of null coalescing operators. <lang csharp> using System; using System.IO; using System.Linq; using System.Collections.Generic;


namespace Rosetta {

   public enum TokenType {
       End_of_input, Op_multiply, Op_divide, Op_mod, Op_add, Op_subtract,
       Op_negate, Op_not, Op_less, Op_lessequal, Op_greater, Op_greaterequal,
       Op_equal, Op_notequal, Op_assign, Op_and, Op_or, Keyword_if,
       Keyword_else, Keyword_while, Keyword_print, Keyword_putc, LeftParen, RightParen,
       LeftBrace, RightBrace, Semicolon, Comma, Identifier, Integer, String, None
   }
   /// <summary>
   /// Storage class for tokens
   /// </summary>
   public class Token {
       public TokenType Type { get; set; }
       public int Line { get; set; }
       public int Position { get; set; }
       public string Value { get; set; }
       public override string ToString() {
           if (Type == TokenType.Integer || Type == TokenType.Identifier) {
               return String.Format("{0,-5}  {1,-5}   {2,-14}     {3}", Line, Position, Type.ToString(), Value);
           } else if (Type == TokenType.String) {
               return String.Format("{0,-5}  {1,-5}   {2,-14}     \"{3}\"", Line, Position, Type.ToString(), Value.Replace("\n", "\\n"));
           }
           return String.Format("{0,-5}  {1,-5}   {2,-14}", Line, Position, Type.ToString());
       }
   }
   /// <summary>
   /// C# Example of Lexical scanner for Rosetta Compiler
   /// </summary>
   public class LexicalScanner {
       // character classes 
       private const string _letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_";        
       private const string _numbers = "0123456789";
       private const string _identifier = _letters + _numbers + "_";
       private const string _whitespace = " \t\n\r";
       
       // mappings from string keywords to token type 
       private Dictionary<string, TokenType> _keywordTokenTypeMap = new Dictionary<string, TokenType>() {
           { "if", TokenType.Keyword_if },
           { "else", TokenType.Keyword_else },
           { "while", TokenType.Keyword_while },
           { "print", TokenType.Keyword_print },
           { "putc", TokenType.Keyword_putc }
       };
       // mappings from simple operators to token type
       private Dictionary<string, TokenType> _operatorTokenTypeMap = new Dictionary<string, TokenType>() {
           { "+", TokenType.Op_add },
           { "-", TokenType.Op_subtract },
           { "*", TokenType.Op_multiply },
           { "/", TokenType.Op_divide },
           { "%", TokenType.Op_mod },
           { "=", TokenType.Op_assign },
           { "<", TokenType.Op_less },
           { ">", TokenType.Op_greater },
           { "!", TokenType.Op_not },
       };
       private List<string> _keywords;
       private string _operators = "+-*/%=<>!%";
       private string _code;
       private List<Token> tokens = new List<Token>();
       private int _line = 1;
       private int _position = 1;
       public string CurrentCharacter {
           get {
               try {
                   return _code.Substring(0, 1);
               } catch (ArgumentOutOfRangeException) {
                   return "";
               }
           }
       }
       /// <summary>
       /// Lexical scanner initialiser
       /// </summary>
       /// <param name="code">Code to be tokenised</param>
       public LexicalScanner (string code) {
           _code = code;
           _keywords = _keywordTokenTypeMap.Keys.ToList();
       }
       /// <summary>
       /// Advance the cursor forward given number of characters
       /// </summary>
       /// <param name="characters">Number of characters to advance</param>
       private void advance(int characters=1) {
           try {
               // reset position when there is a newline
               if (CurrentCharacter == "\n") {
                   _position = 0;
                   _line++;
               }
                   
               _code = _code.Substring(characters, _code.Length - characters);
               _position += characters;
           } catch (ArgumentOutOfRangeException) {
               _code = "";
           }
       }
       /// <summary>
       /// Outputs error message to the console and exits 
       /// </summary>
       /// <param name="message">Error message to display to user</param>
       /// <param name="line">Line error occurred on</param>
       /// <param name="position">Line column that the error occurred at</param>
       public void error(string message, int line, int position) {
           // output error to the console and exit
           Console.WriteLine(String.Format("{0} @ {1}:{2}", message, line, position));
           Environment.Exit(1);
       }
       /// <summary>
       /// Pattern matching using first & follow matching
       /// </summary>
       /// <param name="recogniseClass">String of characters that identifies the token type
       /// or the exact match the be made if exact:true</param>
       /// <param name="matchClass">String of characters to match against remaining target characters</param>
       /// <param name="tokenType">Type of token the match represents.</param>
       /// <param name="notNextClass">Optional class of characters that cannot follow the match</param>
       /// <param name="maxLen">Optional maximum length of token value</param>
       /// <param name="exact">Denotes whether recogniseClass represents an exact match or class match. 
       /// Default: false</param>
       /// <param name="discard">Denotes whether the token is kept or discarded. Default: false</param>
       /// <param name="offset">Optiona line position offset to account for discarded tokens</param>
       /// <returns>Boolean indicating if a match was made </returns>
       public bool match(string recogniseClass, string matchClass, TokenType tokenType, 
                         string notNextClass=null, int maxLen=Int32.MaxValue, bool exact=false, 
                         bool discard=false, int offset=0) {
           // if we've hit the end of the file, there's no more matching to be done
           if (CurrentCharacter == "")
               return false;
           // store _current_ line and position so that our vectors point at the start
           // of each token
           int line = _line;
           int position = _position;
           // special case exact tokens to avoid needing to worry about backtracking
           if (exact) {
               if (_code.StartsWith(recogniseClass)) {
                   if (!discard) 
                       tokens.Add(new Token() { Type = tokenType, Value = recogniseClass, Line = line, Position = position - offset});   
                   advance(recogniseClass.Length);
                   return true;
               }
               return false;
           }
           // first match - denotes the token type usually
           if (!recogniseClass.Contains(CurrentCharacter))
               return false;
           string tokenValue = CurrentCharacter;
           advance();
           // follow match while we haven't exceeded maxLen and there are still characters
           // in the code stream
           while ((matchClass ?? "").Contains(CurrentCharacter) && tokenValue.Length <= maxLen && CurrentCharacter != "") {
               tokenValue += CurrentCharacter;
               advance();
           }
           // ensure that any incompatible characters are not next to the token
           // eg 42fred is invalid, and neither recognized as a number nor an identifier.
           // _letters would be the notNextClass
           if (notNextClass != null && notNextClass.Contains(CurrentCharacter))
               error("Unrecognised character: " + CurrentCharacter, _line, _position);
           // only add tokens to the stack that aren't marked as discard - dont want
           // things like open and close quotes/comments
           if (!discard) {
               Token token = new Token() { Type = tokenType, Value = tokenValue, Line = line, Position = position - offset };
               tokens.Add(token);
           }
           return true;
       }
       /// <summary>
       /// Tokenise the input code 
       /// </summary>
       /// <returns>List of Tokens</returns>
       public List<Token> scan() {
           while (CurrentCharacter != "") {
               // match whitespace
               match(_whitespace, _whitespace, TokenType.None, discard: true);
               // match integers
               match(_numbers, _numbers, TokenType.Integer, notNextClass:_letters);
               
               // match identifiers and keywords
               if (match(_letters, _identifier, TokenType.Identifier)) {
                   Token match = tokens.Last();
                   if (_keywords.Contains(match.Value))
                       match.Type = _keywordTokenTypeMap[match.Value];
               }
               // match string similarly to comments without allowing newlines
               // this token doesn't get discarded though
               if (match("\"", null, TokenType.String, discard:true)) {
                   string value = "";
                   int position = _position;
                   while (!match("\"", null, TokenType.String, discard:true)) {
                       // not allowed newlines in strings
                       if (CurrentCharacter == "\n")
                           error("End-of-line while scanning string literal. Closing string character not found before end-of-line", _line, _position);
                       // end of file reached before finding end of string
                       if (CurrentCharacter == "")
                           error("End-of-file while scanning string literal. Closing string character not found", _line, _position);
                       value += CurrentCharacter;
                       // deal with escape sequences - we only accept newline (\n)
                       if (value.Length >= 2) {
                           string lastCharacters = value.Substring(value.Length - 2, 2);
                           if (lastCharacters[0] == '\\') {
                               if (lastCharacters[1] != 'n') {
                                   error("Unknown escape sequence. ", _line, position);
                               }
                               value = value.Substring(0, value.Length - 2).ToString() + "\n";
                           }
                       }
                       advance();
                   }
                   tokens.Add(new Token() { Type = TokenType.String, Value = value, Line = _line, Position = position - 1});
               }
               // match string literals
               if (match("'", null, TokenType.Integer, discard:true)) {
                   int value;
                   int position = _position;
                   value = CurrentCharacter.ToCharArray()[0];
                   advance();
                   // deal with empty literals 
                   if (value == '\)
                       error("Empty character literal", _line, _position);
                   // deal with escaped characters, only need to worry about \n and \\
                   // throw werror on any other
                   if (value == '\\') {
                       if (CurrentCharacter == "n") {
                           value = '\n';
                       } else if (CurrentCharacter == "\\") {
                           value = '\\';
                       } else {
                           error("Unknown escape sequence. ", _line, _position - 1);
                       }
                       advance();
                   }
                   // if we haven't hit a closing ' here, there are two many characters
                   // in the literal
                   if (!match("'", null, TokenType.Integer, discard: true))
                       error("Multi-character constant", _line, _position);
                   tokens.Add(new Rosetta.Token() { Type = TokenType.Integer, Value = value.ToString(), Line = _line, Position = position - 1 });
               }
               // match comments by checking for starting token, then advancing 
               // until closing token is matched
               if (match("/*", null, TokenType.None, exact: true, discard: true)) {
                   while (!match("*/", null, TokenType.None, exact: true, discard: true)) {
                       // reached the end of the file without closing comment!
                       if (CurrentCharacter == "")
                           error("End-of-file in comment. Closing comment characters not found.", _line, _position);
                       advance();
                   }
                   continue;
               }
               // match complex operators
               match("<=", null, TokenType.Op_lessequal, exact: true);
               match(">=", null, TokenType.Op_greaterequal, exact: true);
               match("==", null, TokenType.Op_equal, exact: true);
               match("!=", null, TokenType.Op_notequal, exact: true);
               match("&&", null, TokenType.Op_and, exact: true);
               match("||", null, TokenType.Op_or, exact: true);
               // match simple operators
               if (match(_operators, null, TokenType.None, maxLen:1)) {
                   Token match = tokens.Last();
                   match.Type = _operatorTokenTypeMap[match.Value];
               }
               // brackets, braces and separators
               match("(", null, TokenType.LeftParen, exact: true);
               match(")", null, TokenType.RightParen, exact: true);
               match("{", null, TokenType.LeftBrace, exact: true);
               match("}", null, TokenType.RightBrace, exact: true);
               match(";", null, TokenType.Semicolon, exact: true);
               match(",", null, TokenType.Comma, exact: true);
           }
           // end of file token
           tokens.Add(new Rosetta.Token() { Type = TokenType.End_of_input, Line = _line, Position = _position });
           
           return tokens;
       }
       static void Main (string[] args) {
           StreamReader inputFile;
           // if we passed in a filename, read code from that, else
           // read code from stdin
           if (args.Length > 0) {
               string path = args[0];
               try {
                   inputFile = new StreamReader(path);
               } catch (IOException) {
                   inputFile = new StreamReader(Console.OpenStandardInput(8192));
               }
           } else {
               inputFile = new StreamReader(Console.OpenStandardInput(8192));
           }
           string code = inputFile.ReadToEnd();
           // strip windows line endings out
           code = code.Replace("\r", "");
           LexicalScanner scanner = new LexicalScanner(code);
           List<Token> tokens = scanner.scan();
           foreach(Token token in tokens) {
               Console.WriteLine(token.ToString());
           }       
       }
   }

} </lang>

Output  —  test case 3:

5      16      Keyword_print
5      40      Op_subtract
6      16      Keyword_putc
6      40      Op_less
7      16      Keyword_if
7      40      Op_greater
8      16      Keyword_else
8      40      Op_lessequal
9      16      Keyword_while
9      40      Op_greaterequal
10     16      LeftBrace
10     40      Op_equal
11     16      RightBrace
11     40      Op_notequal
12     16      LeftParen
12     40      Op_and
13     16      RightParen
13     40      Op_or
14     16      Op_subtract
14     40      Semicolon
15     16      Op_not
15     40      Comma
16     16      Op_multiply
16     40      Op_assign
17     16      Op_divide
17     40      Integer            42
18     16      Op_mod
18     40      String             "String literal"
19     16      Op_add
19     40      Identifier         variable_name
20     26      Integer            10
21     26      Integer            92
22     26      Integer            32
23     1       End_of_input

COBOL

Using GnuCOBOL 2. By Steve Williams (with one change to get around a Rosetta Code code highlighter problem).

<lang cobol> >>SOURCE FORMAT IS FREE

  • > this code is dedicated to the public domain
  • > (GnuCOBOL) 2.3-dev.0

identification division. program-id. lexer. environment division. configuration section. repository. function all intrinsic. input-output section. file-control.

   select input-file assign using input-name
       status input-status
       organization line sequential.

data division.

file section. fd input-file. 01 input-record pic x(98).

working-storage section. 01 input-name pic x(32). 01 input-status pic xx. 01 input-length pic 99.

01 output-name pic x(32) value spaces. 01 output-status pic xx. 01 output-record pic x(64).

01 line-no pic 999 value 0. 01 col-no pic 99. 01 col-no-max pic 99. 01 col-increment pic 9 value 1. 01 start-col pic 99. 01 outx pic 99. 01 out-lim pic 99 value 48.

01 output-line value spaces.

   03  out-line pic zzzz9.
   03  out-column pic zzzzzz9.
   03  message-area.
       05  filler pic xxx.
       05  token pic x(16).
       05  out-value pic x(48).
       05  out-integer redefines out-value pic zzzzz9.
       05  out-integer1 redefines out-value pic zzzzzz9. *> to match the python lexer

01 error-record.

   03  error-line pic zzzz9 value 0.
   03  error-col pic zzzzzz9 value 0.
   03  error-message pic x(68) value spaces.

01 scan-state pic x(16) value spaces. 01 current-character pic x. 01 previous-character pic x.

procedure division chaining input-name. start-lexer.

   if input-name <> spaces
       open input input-file
       if input-status = '35'
           string 'in lexer ' trim(input-name) ' not found' into error-message
           perform report-error
       end-if
   end-if
   perform read-input-file
   perform until input-status <> '00'
       add 1 to line-no
       move line-no to out-line
       move length(trim(input-record,trailing)) to col-no-max
       move 1 to col-no
       move space to previous-character
       perform until col-no > col-no-max
           move col-no to out-column
           move input-record(col-no:1) to current-character
           evaluate scan-state
           when 'identifier'
               if current-character >= 'A' and <= 'Z'
               or (current-character >= 'a' and <= 'z')
               or (current-character >= '0' and <= '9')
               or current-character = '_'
                   perform increment-outx
                   move current-character to out-value(outx:1)
                   if col-no = col-no-max
                       perform process-identifier
                   end-if
               else
                   perform process-identifier
                   if current-character <> space
                       move 0 to col-increment
                   end-if
               end-if
           when 'integer'
               evaluate true
               when current-character >= '0' and <= '9'
                   perform increment-outx
                   move current-character to out-value(outx:1)
                   if col-no = col-no-max
                       move numval(out-value) to out-integer
                       move 'Integer' to token
                   end-if
               when current-character >= 'A' and <= 'Z'
               when current-character >= 'a' and <= 'z'
                   move 'in lexer invalid integer' to error-message
                   perform report-error
               when other
                   if outx > 5
                       move numval(out-value) to out-integer1 *> to match the python lexer
                   else
                       move numval(out-value) to out-integer
                   end-if
                   move 'Integer' to token
                   if current-character <> space
                       move 0 to col-increment
                   end-if
               end-evaluate
               
           when 'comment'
               if previous-character = '*' and current-character = '/' 
                   move 'comment' to token
               end-if
           when 'quote'
               evaluate current-character also outx
               when '"' also 0
                   string 'in lexer empty string' into error-message
                   perform report-error
               when '"' also any
                   perform increment-outx
                   move current-character to out-value(outx:1)
                   move 'String' to token
               when other
                   if col-no = col-no-max
                       string 'in lexer missing close quote' into error-message
                       perform report-error
                   else
                       perform increment-outx
                       move current-character to out-value(outx:1)
                   end-if
               end-evaluate
           when 'character'
               evaluate current-character also outx
               when "'" also 0
                   string 'in lexer empty character constant' into error-message
                   perform report-error
               when "'" also 1
                   subtract 1 from ord(out-value(1:1)) giving out-integer
                   move 'Integer' to token
               when "'" also 2
                   evaluate true 
                   when out-value(1:2) = '\n'
                       move 10 to out-integer
                   when out-value(1:2) = '\\'
                       subtract 1 from ord('\') giving out-integer      *> ' (workaround a Rosetta Code highlighter problem)
                   when other
                       string 'in lexer unknown escape sequence ' out-value(1:2)
                           into error-message
                       perform report-error
                   end-evaluate
                   move 'Integer' to token
               when "'" also any
                   string 'in lexer multicharacter constant' into error-message
                   perform report-error
               when other
                   if col-no = col-no-max
                       string 'in lexer missing close quote' into error-message
                       perform report-error
                   end-if
                   perform increment-outx
                   move current-character to out-value(outx:1)
               end-evaluate
           when 'and'
               evaluate previous-character also current-character
               when '&' also '&'
                   move 'Op_and' to token
               when other
                   string 'in lexer AND error' into error-message
                   perform report-error
               end-evaluate
           when 'or'
               evaluate previous-character also current-character
               when '|' also '|'
                   move 'Op_or' to token
               when other
                   string 'in lexer OR error' into error-message
                   perform report-error
               end-evaluate
           when 'ambiguous'
               evaluate previous-character also current-character
               when '/' also '*'
                   move 'comment' to scan-state
                   subtract 1 from col-no giving start-col
               when '/' also any
                   move 'Op_divide' to token
                   move 0 to col-increment
               when '=' also '='
                   move 'Op_equal' to token
               when '=' also any
                   move 'Op_assign' to token
                   move 0 to col-increment
               when '<' also '='
                   move 'Op_lessequal' to token
               when '<' also any
                   move 'Op_less' to token 
                   move 0 to col-increment
               when '>' also '='
                   move 'Op_greaterequal' to token
               when '>'also any
                   move 'Op_greater' to token
                   move 0 to col-increment
               when '!' also '='
                   move 'Op_notequal' to token
               when '!' also any
                   move 'Op_not' to token
                   move 0 to col-increment
               when other
                   display input-record
                   string 'in lexer ' trim(scan-state)
                       ' unknown character "' current-character '"'
                       ' with previous character "' previous-character '"'
                       into error-message
                   perform report-error
               end-evaluate
           when other
               move col-no to start-col
               evaluate current-character
               when space
                   continue
               when >= 'A' and <= 'Z'
               when >= 'a' and <= 'z'
                   move 'identifier' to scan-state
                   move 1 to outx
                   move current-character to out-value
               when >= '0' and <= '9'
                   move 'integer' to scan-state
                   move 1 to outx
                   move current-character to out-value
               when '&'
                   move 'and' to scan-state
               when '|'
                   move 'or' to scan-state
               when '"'
                   move 'quote' to scan-state
                   move 1 to outx
                   move current-character to out-value
               when "'"
                   move 'character' to scan-state
                   move 0 to outx
               when '{'
                   move 'LeftBrace' to token
               when '}'
                   move 'RightBrace' to token
               when '('
                   move 'LeftParen' to token
               when ')'
                   move 'RightParen' to token
               when '+'
                   move 'Op_add' to token
               when '-'
                   move 'Op_subtract' to token
               when '*'
                   move 'Op_multiply' to token
               when '%'
                   move 'Op_mod' to token
               when ';'
                   move 'Semicolon' to token
               when ','
                   move 'Comma' to token
               when '/'
               when '<'
               when '>'
               when '='
               when '='
               when '<'
               when '>'
               when '!'
                   move 'ambiguous' to scan-state
               when other
                   string 'in lexer unknown character "' current-character '"'
                       into error-message
                   perform report-error
               end-evaluate
           end-evaluate
           if token <> spaces
               perform process-token
           end-if
           move current-character to previous-character
           add col-increment to col-no
           move 1 to col-increment
       end-perform
       if scan-state = 'ambiguous'
           evaluate previous-character
           when '/'
               move 'Op_divide' to token
               perform process-token
           when '='
               move 'Op_assign' to token
               perform process-token
           when '<'
               move 'Op_less' to token 
               perform process-token
           when '>'
               move 'Op_greater' to token
               perform process-token
           when '!'
               move 'Op_not' to token
               perform process-token
           when other
               string 'in lexer unresolved ambiguous
                   "' previous-character '" at end of line'
               into error-message
               perform report-error
           end-evaluate
       end-if
       perform read-input-file
   end-perform
   evaluate true
   when input-status <> '10'
       string 'in lexer ' trim(input-name) ' invalid input status ' input-status
           into error-message
       perform report-error
   when scan-state = 'comment'
       string 'in lexer unclosed comment at end of input' into error-message
       perform report-error
    end-evaluate
   
   move 'End_of_input' to token
   move 1 to out-column
   move 1 to start-col
   add 1 to line-no
   perform process-token
   close input-file
   stop run
   .

process-identifier.

   evaluate true
   when out-value = 'print'
       move 'Keyword_print' to token
       move spaces to out-value
   when out-value = 'while'
       move 'Keyword_while' to token
       move spaces to out-value
   when out-value = 'if'
       move 'Keyword_if' to token
       move spaces to out-value
   when out-value = 'else'
       move 'Keyword_else' to token
       move spaces to out-value
   when out-value = 'putc'
       move 'Keyword_putc' to token
       move spaces to out-value
   when other
       move 'Identifier' to token
   end-evaluate
   .

increment-outx.

   if outx >= out-lim
       string 'in lexer token value length exceeds ' out-lim into error-message
       perform report-error
   end-if
   add 1 to outx
   .

process-token.

   if token <> 'comment'
       move start-col to out-column
       move line-no to out-line
       display output-line
   end-if
   move 0 to start-col
   move spaces to scan-state message-area
   .

report-error.

   move line-no to error-line
   move start-col to error-col
   display error-record
   close input-file
   stop run with error status -1
   .

read-input-file.

   if input-name = spaces
       move '00' to input-status
       accept input-record on exception move '10' to input-status end-accept
   else
       read input-file
   end-if
   .

end program lexer.</lang>

Output  —  test case 3:
prompt$ ./lexer <testcase3
    5     16   Keyword_print
    5     40   Op_subtract
    6     16   Keyword_putc
    6     40   Op_less
    7     16   Keyword_if
    7     40   Op_greater
    8     16   Keyword_else
    8     40   Op_lessequal
    9     16   Keyword_while
    9     40   Op_greaterequal
   10     16   LeftBrace
   10     40   Op_equal
   11     16   RightBrace
   11     40   Op_notequal
   12     16   LeftParen
   12     40   Op_and
   13     16   RightParen
   13     40   Op_or
   14     16   Op_subtract
   14     40   Semicolon
   15     16   Op_not
   15     40   Comma
   16     16   Op_multiply
   16     40   Op_assign
   17     16   Op_divide
   17     40   Integer             42
   18     16   Op_mod
   18     40   String          "String literal"
   19     16   Op_add
   19     40   Identifier      variable_name
   20     26   Integer             10
   21     26   Integer             92
   22     26   Integer             32
   23      1   End_of_input

Common Lisp

Lisp has a built-in reader and you can customize the reader by modifying its readtable. I'm also using the Gray stream, which is an almost standard feature of Common Lisp, for counting lines and columns.

<lang lisp>(defpackage #:lexical-analyzer

 (:use #:cl #:sb-gray)
 (:export #:main))

(in-package #:lexical-analyzer)

(defconstant +lex-symbols-package+ (or (find-package :lex-symbols)

                                      (make-package :lex-symbols)))

(defclass counting-character-input-stream (fundamental-character-input-stream)

 ((stream :type stream :initarg :stream :reader stream-of)
  (line :type fixnum :initform 1 :accessor line-of)
  (column :type fixnum :initform 0 :accessor column-of)
  (prev-column :type (or null fixnum) :initform nil :accessor prev-column-of))
 (:documentation "Character input stream that counts lines and columns."))

(defmethod stream-read-char ((stream counting-character-input-stream))

 (let ((ch (read-char (stream-of stream) nil :eof)))
   (case ch
     (#\Newline
      (incf (line-of stream))
      (setf (prev-column-of stream) (column-of stream)
            (column-of stream) 0))
     (t
      (incf (column-of stream))))
   ch))

(defmethod stream-unread-char ((stream counting-character-input-stream) char)

 (unread-char char (stream-of stream))
 (case char
     (#\Newline
      (decf (line-of stream))
      (setf (column-of stream) (prev-column-of stream)))
     (t
      (decf (column-of stream)))))

(defstruct token

 (name nil :type symbol)
 (value nil :type t)
 (line nil :type fixnum)
 (column nil :type fixnum))

(defun lexer-error (format-control &rest args)

 (apply #'error format-control args))

(defun handle-divide-or-comment (stream char)

 (declare (ignore char))
 (case (peek-char nil stream t nil t)
   (#\* (loop with may-end = nil
                initially (read-char stream t nil t)
              for ch = (read-char stream t nil t)
              until (and may-end (char= ch #\/))
              do (setf may-end (char= ch #\*))
              finally (return (read stream t nil t))))
   (t (make-token :name :op-divide :line (line-of stream) :column (column-of stream)))))

(defun make-constant-handler (token-name)

 (lambda (stream char)
   (declare (ignore char))
   (make-token :name token-name :line (line-of stream) :column (column-of stream))))

(defun make-this-or-that-handler (expect then &optional else)

 (lambda (stream char)
   (declare (ignore char))
   (let ((line (line-of stream))
         (column (column-of stream))
         (next (peek-char nil stream nil nil t)))
     (cond ((and expect (char= next expect))
            (read-char stream nil nil t)
            (make-token :name then :line line :column column))
           (else
            (make-token :name else :line line :column column))
           (t
            (lexer-error "Unrecognized character '~A'" next))))))

(defun identifier? (symbol)

 (and (symbolp symbol)
      (not (keywordp symbol))
      (let ((name (symbol-name symbol)))
        (and (find (char name 0) "_abcdefghijklmnopqrstuvwxyz" :test #'char-equal)
             (or (< (length name) 2)
                 (not (find-if-not (lambda (ch)
                                     (find ch "_abcdefghijklmnopqrstuvwxyz0123456789"
                                           :test #'char-equal))
                                   name :start 1)))))))

(defun id->keyword (id line column)

 (case id
   (lex-symbols::|if|    (make-token :name :keyword-if :line line :column column))
   (lex-symbols::|else|  (make-token :name :keyword-else :line line :column column))
   (lex-symbols::|while| (make-token :name :keyword-while :line line :column column))
   (lex-symbols::|print| (make-token :name :keyword-print :line line :column column))
   (lex-symbols::|putc|  (make-token :name :keyword-putc :line line :column column))
   (t nil)))

(defun handle-identifier (stream char)

 (let ((*readtable* (copy-readtable)))
   (set-syntax-from-char char #\z)
   (let ((line (line-of stream))
         (column (column-of stream)))
     (unread-char char stream)
     (let ((obj (read stream t nil t)))
       (if (identifier? obj)
           (or (id->keyword obj line column)
               (make-token :name :identifier :value obj :line line :column column))
           (lexer-error "Invalid identifier name: ~A" obj))))))

(defun handle-integer (stream char)

 (let ((*readtable* (copy-readtable)))
   (set-syntax-from-char char #\z)
   (let ((line (line-of stream))
         (column (column-of stream)))
     (unread-char char stream)
     (let ((obj (read stream t nil t)))
       (if (integerp obj)
           (make-token :name :integer :value obj :line line :column column)
           (lexer-error "Invalid integer: ~A" obj))))))

(defun handle-char-literal (stream char)

 (declare (ignore char))
 (let* ((line (line-of stream))
        (column (column-of stream))
        (ch (read-char stream t nil t))
        (parsed (case ch
                  (#\' (lexer-error "Empty character constant"))
                  (#\Newline (lexer-error "New line in character literal"))
                  (#\\ (let ((next-ch (read-char stream t nil t)))
                         (case next-ch
                           (#\n #\Newline)
                           (#\\ #\\)
                           (t (lexer-error "Unknown escape sequence: \\~A" next-ch)))))
                  (t ch))))
   (if (char= #\' (read-char stream t nil t))
       (make-token :name :integer :value (char-code parsed) :line line :column column)
       (lexer-error "Only one character is allowed in character literal"))))

(defun handle-string (stream char)

 (declare (ignore char))
 (loop with result = (make-array 0 :element-type 'character :adjustable t :fill-pointer t)
       with line = (line-of stream)
       with column = (column-of stream)
       for ch = (read-char stream t nil t)
       until (char= ch #\")
       do (setf ch (case ch
                     (#\Newline (lexer-error "New line in string"))
                     (#\\ (let ((next-ch (read-char stream t nil t)))
                            (case next-ch
                              (#\n #\Newline)
                              (#\\ #\\)
                              (t (lexer-error "Unknown escape sequence: \\~A" next-ch)))))
                     (t ch)))
          (vector-push-extend ch result)
       finally (return (make-token :name :string :value result :line line :column column))))

(defun make-lexer-readtable ()

 (let ((*readtable* (copy-readtable nil)))
   (setf (readtable-case *readtable*) :preserve)
   (set-syntax-from-char #\\ #\z)
   (set-syntax-from-char #\# #\z)
   (set-syntax-from-char #\` #\z)
   ;; operators
   (set-macro-character #\* (make-constant-handler :op-multiply))
   (set-macro-character #\/ #'handle-divide-or-comment)
   (set-macro-character #\% (make-constant-handler :op-mod))
   (set-macro-character #\+ (make-constant-handler :op-add))
   (set-macro-character #\- (make-constant-handler :op-subtract))
   (set-macro-character #\< (make-this-or-that-handler #\= :op-lessequal :op-less))
   (set-macro-character #\> (make-this-or-that-handler #\= :op-greaterequal :op-greater))
   (set-macro-character #\= (make-this-or-that-handler #\= :op-equal :op-assign))
   (set-macro-character #\! (make-this-or-that-handler #\= :op-notequal :op-not))
   (set-macro-character #\& (make-this-or-that-handler #\& :op-and))
   (set-macro-character #\| (make-this-or-that-handler #\| :op-or))
   ;; symbols
   (set-macro-character #\( (make-constant-handler :leftparen))
   (set-macro-character #\) (make-constant-handler :rightparen))
   (set-macro-character #\{ (make-constant-handler :leftbrace))
   (set-macro-character #\} (make-constant-handler :rightbrace))
   (set-macro-character #\; (make-constant-handler :semicolon))
   (set-macro-character #\, (make-constant-handler :comma))
   ;; identifiers & keywords
   (set-macro-character #\_ #'handle-identifier t)
   (loop for ch across "abcdefghijklmnopqrstuvwxyz"
         do (set-macro-character ch #'handle-identifier t))
   (loop for ch across "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
         do (set-macro-character ch #'handle-identifier t))
   ;; integers
   (loop for ch across "0123456789"
         do (set-macro-character ch #'handle-integer t))
   (set-macro-character #\' #'handle-char-literal)
   ;; strings
   (set-macro-character #\" #'handle-string)
   *readtable*))

(defun lex (stream)

 (loop with *readtable* = (make-lexer-readtable)
       with *package* = +lex-symbols-package+
       with eof = (gensym)
       with counting-stream = (make-instance 'counting-character-input-stream :stream stream)
       for token = (read counting-stream nil eof)
       until (eq token eof)
       do (format t "~5D ~5D ~15A~@[ ~S~]~%"
                  (token-line token) (token-column token) (token-name token) (token-value token))
       finally (format t "~5D ~5D ~15A~%"
                       (line-of counting-stream) (column-of counting-stream) :end-of-input)
               (close counting-stream)))

(defun main ()

 (lex *standard-input*))</lang>
Output  —  test case 3:
    5    16 KEYWORD-PRINT  
    5    40 OP-SUBTRACT    
    6    16 KEYWORD-PUTC   
    6    40 OP-LESS        
    7    16 KEYWORD-IF     
    7    40 OP-GREATER     
    8    16 KEYWORD-ELSE   
    8    40 OP-LESSEQUAL   
    9    16 KEYWORD-WHILE  
    9    40 OP-GREATEREQUAL
   10    16 LEFTBRACE      
   10    40 OP-EQUAL       
   11    16 RIGHTBRACE     
   11    40 OP-NOTEQUAL    
   12    16 LEFTPAREN      
   12    40 OP-AND         
   13    16 RIGHTPAREN     
   13    40 OP-OR          
   14    16 OP-SUBTRACT    
   14    40 SEMICOLON      
   15    16 OP-NOT         
   15    40 COMMA          
   16    16 OP-MULTIPLY    
   16    40 OP-ASSIGN      
   17    16 OP-DIVIDE      
   17    40 INTEGER         42
   18    16 OP-MOD         
   18    40 STRING          "String literal"
   19    16 OP-ADD         
   19    40 IDENTIFIER      variable_name
   20    26 INTEGER         10
   21    26 INTEGER         92
   22    26 INTEGER         32
   23     1 END-OF-INPUT   

Euphoria

Tested with Euphoria 4.05. <lang euphoria>include std/io.e include std/map.e include std/types.e include std/convert.e

constant true = 1, false = 0, EOF = -1

enum tk_EOI, tk_Mul, tk_Div, tk_Mod, tk_Add, tk_Sub, tk_Negate, tk_Not, tk_Lss, tk_Leq,

   tk_Gtr, tk_Geq, tk_Eq, tk_Neq, tk_Assign, tk_And, tk_Or, tk_If, tk_Else, tk_While,
   tk_Print, tk_Putc, tk_Lparen, tk_Rparen, tk_Lbrace, tk_Rbrace, tk_Semi, tk_Comma,
   tk_Ident, tk_Integer, tk_String

constant all_syms = {"End_of_input", "Op_multiply", "Op_divide", "Op_mod", "Op_add",

   "Op_subtract", "Op_negate", "Op_not", "Op_less", "Op_lessequal", "Op_greater",
   "Op_greaterequal", "Op_equal", "Op_notequal", "Op_assign", "Op_and", "Op_or",
   "Keyword_if", "Keyword_else", "Keyword_while", "Keyword_print", "Keyword_putc",
   "LeftParen", "RightParen", "LeftBrace", "RightBrace", "Semicolon", "Comma",
   "Identifier", "Integer", "String"}

integer input_file, the_ch = ' ', the_col = 0, the_line = 1 sequence symbols map key_words = new()

procedure error(sequence format, sequence data)

   printf(STDOUT, format, data)
   abort(1)

end procedure

-- get the next character from the input function next_ch()

   the_ch = getc(input_file)
   the_col += 1
   if the_ch = '\n' then
       the_line += 1
       the_col = 0
   end if
   return the_ch

end function

-- 'x' - character constants function char_lit(integer err_line, integer err_col)

   integer n = next_ch()              -- skip opening quote
   if the_ch = '\ then
       error("%d %d empty character constant", {err_line, err_col})
   elsif the_ch = '\\' then
       next_ch()
       if the_ch = 'n' then
           n = 10
       elsif the_ch = '\\' then
           n = '\\'
       else
           error("%d %d unknown escape sequence \\%c", {err_line, err_col, the_ch})
       end if
   end if
   if next_ch() != '\ then
       error("%d %d multi-character constant", {err_line, err_col})
   end if
   next_ch()
   return {tk_Integer, err_line, err_col, n}

end function

-- process divide or comments function div_or_cmt(integer err_line, integer err_col)

   if next_ch() != '*' then
       return {tk_Div, err_line, err_col}
   end if
   -- comment found
   next_ch()
   while true do
       if the_ch = '*' then
           if next_ch() = '/' then
               next_ch()
               return get_tok()
           end if
       elsif the_ch = EOF then
           error("%d %d EOF in comment", {err_line, err_col})
       else
           next_ch()
       end if
   end while

end function

-- "string" function string_lit(integer start, integer err_line, integer err_col)

   string text = ""
   while next_ch() != start do
       if the_ch = EOF then
           error("%d %d EOF while scanning string literal", {err_line, err_col})
       end if
       if the_ch = '\n' then
           error("%d %d EOL while scanning string literal", {err_line, err_col})
       end if
       text &= the_ch
   end while
   next_ch()
   return {tk_String, err_line, err_col, text}

end function

-- handle identifiers and integers function ident_or_int(integer err_line, integer err_col)

   integer n, is_number = true
   string text = ""
   while t_alnum(the_ch) or the_ch = '_' do
       text &= the_ch
       if not t_digit(the_ch) then
           is_number = false
       end if
       next_ch()
   end while
   if length(text) = 0 then
       error("%d %d ident_or_int: unrecognized character: (%d) '%s'", {err_line, err_col, the_ch, the_ch})
   end if
   if t_digit(text[1]) then
       if not is_number then
           error("%d %d invalid number: %s", {err_line, err_col, text})
       end if
       n = to_integer(text)
       return {tk_Integer, err_line, err_col, n}
   end if
   if has(key_words, text) then
       return {get(key_words, text), err_line, err_col}
   end if
   return {tk_Ident, err_line, err_col, text}

end function

-- look ahead for '>=', etc. function follow(integer expect, integer ifyes, integer ifno, integer err_line, integer err_col)

   if next_ch() = expect then
       next_ch()
       return {ifyes, err_line, err_col}
   end if
   if ifno = tk_EOI then
       error("%d %d follow: unrecognized character: (%d)", {err_line, err_col, the_ch})
   end if
   return {ifno, err_line, err_col}

end function

-- return the next token type function get_tok()

   while t_space(the_ch) do
       next_ch()
   end while
   integer err_line = the_line
   integer err_col  = the_col
   switch the_ch do
       case EOF  then return {tk_EOI, err_line, err_col}
       case '/'  then return div_or_cmt(err_line, err_col)
       case '\ then return char_lit(err_line, err_col)
       case '<'  then return follow('=', tk_Leq, tk_Lss,    err_line, err_col)
       case '>'  then return follow('=', tk_Geq, tk_Gtr,    err_line, err_col)
       case '='  then return follow('=', tk_Eq,  tk_Assign, err_line, err_col)
       case '!'  then return follow('=', tk_Neq, tk_Not,    err_line, err_col)
       case '&'  then return follow('&', tk_And, tk_EOI,    err_line, err_col)
       case '|'  then return follow('|', tk_Or,  tk_EOI,    err_line, err_col)
       case '"'  then return string_lit(the_ch, err_line, err_col)
       case else
           integer sym = symbols[the_ch]
           if sym  != tk_EOI then
               next_ch()
               return {sym, err_line, err_col}
           end if
           return ident_or_int(err_line, err_col)
   end switch

end function

procedure init()

   put(key_words, "else",    tk_Else)
   put(key_words, "if",      tk_If)
   put(key_words, "print",   tk_Print)
   put(key_words, "putc",    tk_Putc)
   put(key_words, "while",   tk_While)
   symbols = repeat(tk_EOI, 256)
   symbols['{'] = tk_Lbrace
   symbols['}'] = tk_Rbrace
   symbols['('] = tk_Lparen
   symbols[')'] = tk_Rparen
   symbols['+'] = tk_Add
   symbols['-'] = tk_Sub
   symbols['*'] = tk_Mul
   symbols['%'] = tk_Mod
   symbols[';'] = tk_Semi
   symbols[','] = tk_Comma

end procedure

procedure main(sequence cl)

   sequence file_name
   input_file = STDIN
   if length(cl) > 2 then
       file_name = cl[3]
       input_file = open(file_name, "r")
       if input_file = -1 then
           error("Could not open %s", {file_name})
       end if
   end if
   init()
   sequence t
   loop do
       t = get_tok()
       printf(STDOUT, "%5d  %5d %-8s", {t[2], t[3], all_syms[t[1]]})
       switch t[1] do
           case tk_Integer then printf(STDOUT, "  %5d\n",   {t[4]})
           case tk_Ident   then printf(STDOUT, " %s\n",     {t[4]})
           case tk_String  then printf(STDOUT, " \"%s\"\n", {t[4]})
           case else            printf(STDOUT, "\n")
       end switch
       until t[1] = tk_EOI
   end loop

end procedure

main(command_line())</lang>

Output  —  test case 3:

    5     16 Keyword_print
    5     40 Op_subtract
    6     16 Keyword_putc
    6     40 Op_less
    7     16 Keyword_if
    7     40 Op_greater
    8     16 Keyword_else
    8     40 Op_lessequal
    9     16 Keyword_while
    9     40 Op_greaterequal
   10     16 LeftBrace
   10     40 Op_equal
   11     16 RightBrace
   11     40 Op_notequal
   12     16 LeftParen
   12     40 Op_and
   13     16 RightParen
   13     40 Op_or
   14     16 Op_subtract
   14     40 Semicolon
   15     16 Op_not
   15     40 Comma
   16     16 Op_multiply
   16     40 Op_assign
   17     16 Op_divide
   17     40 Integer      42
   18     16 Op_mod
   18     40 String   "String literal"
   19     16 Op_add
   19     40 Identifier variable_name
   20     26 Integer      10
   21     26 Integer      92
   22     26 Integer      32
   23      1 End_of_input

Flex

Tested with Flex 2.5.4. <lang C>%{

  1. include <stdio.h>
  2. include <stdlib.h>
  3. include <string.h>
  4. include <errno.h>
  5. include <limits.h>
  1. define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))

typedef enum {

   tk_EOI, tk_Mul, tk_Div, tk_Mod, tk_Add, tk_Sub, tk_Negate, tk_Not, tk_Lss, tk_Leq,
   tk_Gtr, tk_Geq, tk_Eq, tk_Neq, tk_Assign, tk_And, tk_Or, tk_If, tk_Else, tk_While,
   tk_Print, tk_Putc, tk_Lparen, tk_Rparen, tk_Lbrace, tk_Rbrace, tk_Semi, tk_Comma,
   tk_Ident, tk_Integer, tk_String

} TokenType;

void yyerror(char msg[]) {

   printf(msg);
   exit(1);

}

static int yynval;

struct yylloc {

   int first_line, first_col;
   int last_line, last_col;

} yylloc;

static void update_loc() {

 static int curr_line = 1;
 static int curr_col  = 1;
 yylloc.first_line = curr_line;
 yylloc.first_col  = curr_col;
 {char *s; for (s = yytext; *s != '\0'; s++) {
   if (*s == '\n') {
     curr_line++;
     curr_col = 1;
   } else {
     curr_col++;
   }
 }}
 yylloc.last_line = curr_line;
 yylloc.last_col  = curr_col-1;

}

  1. define YY_USER_ACTION update_loc();

static int kwd_cmp(const void *p1, const void *p2) {

   return strcmp(*(char **)p1, *(char **)p2);

}

static TokenType get_ident_type(const char *ident) {

   static struct {
       char *s;
       TokenType sym;
   } kwds[] = {
       {"else",  tk_Else},
       {"if",    tk_If},
       {"print", tk_Print},
       {"putc",  tk_Putc},
       {"while", tk_While},
   }, *kwp;
   return (kwp = bsearch(&ident, kwds, NELEMS(kwds), sizeof(kwds[0]), kwd_cmp)) == NULL ? tk_Ident : kwp->sym;

}

%}

%start COMMENT2

%option noyywrap

digit [0-9] ident [a-zA-Z_][a-zA-Z_0-9]*

number {digit}+ string \"[^"\n]*\" char_const \'([^'\n]|\\n|\\\\)\'

%%

<COMMENT2>[^*]+  ; <COMMENT2>\*[^/] ; <COMMENT2>\*\/ BEGIN 0; /* end comment */ "/*" BEGIN COMMENT2;

"{" {return tk_Lbrace;} "}" {return tk_Rbrace;} "(" {return tk_Lparen;} ")" {return tk_Rparen;} "*" {return tk_Mul;} "/" {return tk_Div;} "%" {return tk_Mod;} "+" {return tk_Add;} "-" {return tk_Sub;} "<" {return tk_Lss;} ">" {return tk_Gtr;} "<=" {return tk_Leq;} ">=" {return tk_Geq;} "!=" {return tk_Neq;} "!" {return tk_Not;} "&&" {return tk_And;} "||" {return tk_Or;} ";" {return tk_Semi;} "," {return tk_Comma;} "==" {return tk_Eq;} "=" {return tk_Assign;} {ident} {return get_ident_type(yytext);} {string} {return tk_String;}

[ \t\n]+ ; /* ignore whitespace */

{number} {

               yynval = strtol(yytext, NULL, 0);
               if (yynval == LONG_MAX && errno == ERANGE)
                   yyerror("Number exceeds maximum value");
               return tk_Integer;
            }

{char_const} {

               int n = yytext[1];
               char *p = yytext;
               if (yyleng < 3)
                   yyerror("empty character constant");
               ++p;
               if (p[0] == '\\') {
                   ++p;
                   if (p[0] == 'n')
                       n = 10;
                   else if (p[0] == '\\')
                       n = '\\';
                   else
                       yyerror("unknown escape sequence");
               }
               yynval = n;
               return tk_Integer;
            }

. yyerror("Unknown character\n");

%%

int main(int argc, char *argv[]) {

   int tok;
   ++argv, --argc;  /* skip over program name */
   yyin = stdin;
   if (argc > 0)
       yyin = fopen(argv[0], "r");
   do {
       tok = yylex();
       printf("%5d  %5d %.15s", yylloc.first_line, yylloc.first_col,
           &"End_of_input    Op_multiply     Op_divide       Op_mod          Op_add          "
            "Op_subtract     Op_negate       Op_not          Op_less         Op_lessequal    "
            "Op_greater      Op_greaterequal Op_equal        Op_notequal     Op_assign       "
            "Op_and          Op_or           Keyword_if      Keyword_else    Keyword_while   "
            "Keyword_print   Keyword_putc    LeftParen       RightParen      LeftBrace       "
            "RightBrace      Semicolon       Comma           Identifier      Integer         "
            "String          "
           [tok * 16]);
       if (tok == tk_Integer)     printf("   %5d", yynval);
       else if (tok == tk_Ident)  printf("  %s",   yytext);
       else if (tok == tk_String) printf("  %s",   yytext);
       printf("\n");
   } while (tok != tk_EOI);
   return 0;

}</lang>

Output  —  test case 3:

    5     16 Keyword_print
    5     40 Op_subtract
    6     16 Keyword_putc
    6     40 Op_less
    7     16 Keyword_if
    7     40 Op_greater
    8     16 Keyword_else
    8     40 Op_lessequal
    9     16 Keyword_while
    9     40 Op_greaterequal
   10     16 LeftBrace
   10     40 Op_equal
   11     16 RightBrace
   11     40 Op_notequal
   12     16 LeftParen
   12     40 Op_and
   13     16 RightParen
   13     40 Op_or
   14     16 Op_subtract
   14     40 Semicolon
   15     16 Op_not
   15     40 Comma
   16     16 Op_multiply
   16     40 Op_assign
   17     16 Op_divide
   17     40 Integer              42
   18     16 Op_mod
   18     40 String           "String literal"
   19     16 Op_add
   19     40 Identifier       variable_name
   20     26 Integer              10
   21     26 Integer              92
   22     26 Integer              32
   22     29 End_of_input

Forth

Tested with Gforth 0.7.3. <lang Forth>CREATE BUF 0 , \ single-character look-ahead buffer CREATE COLUMN# 0 , CREATE LINE# 1 ,

NEWLINE? ( c -- t|f) DUP 10 = SWAP 13 = OR ;
+IN ( c --)
  1 SWAP  NEWLINE?
  IF 0 COLUMN# ! LINE# ELSE COLUMN# THEN
  +!  0 BUF ! ;
PEEK BUF @ 0= IF STDIN KEY-FILE BUF ! THEN BUF @ ;
GETC PEEK DUP +IN ;
SKIP GETC DROP ;
.LOCATION 7 .R 4 .R SPACE ;
WHERE COLUMN# @ LINE# @ ;
.WHERE WHERE .LOCATION ;
.WHERE+ WHERE SWAP 1+ SWAP .LOCATION ;
EXPECT GETC OVER OVER =
  IF 2DROP
  ELSE CR ." stdin:" COLUMN# @ 0 LINE# @ 0
     <# #s #> TYPE ." :" <# #s #> TYPE ." : "
     ." unexpected `" EMIT ." ', expecting `" EMIT ." '" CR
     BYE
  THEN ;
EQ PEEK [CHAR] = = IF SKIP 2SWAP THEN
      ." Op_" TYPE CR  2DROP ;

CREATE ESC 4 C, CHAR $ C, CHAR $ C, CHAR \ C, 0 C,

?ESC? CR ." Unknown escape sequence `\" EMIT ." '" CR BYE ;
>ESC ESC 4 + C! ESC ;
$$\n 10 ;
$$\\ [CHAR] \ ;
ESCAPE DUP >ESC FIND IF NIP EXECUTE ELSE DROP ?ESC? THEN ;
?ESCAPE DUP [CHAR] \ = IF DROP GETC ESCAPE THEN ;
?EOF DUP 4 = IF CR ." End-of-file in string" CR BYE THEN ;
?EOL DUP NEWLINE?
        IF CR ." End-of-line in string" CR BYE THEN ;
STRING PAD
  BEGIN  GETC ?EOF ?EOL DUP  [CHAR] " <>
  WHILE  OVER C! CHAR+
  REPEAT DROP  PAD TUCK - ;
"TYPE" [CHAR] " EMIT TYPE [CHAR] " EMIT ;

CREATE TOKEN 4 C, CHAR $ C, CHAR $ C, 0 C, 0 C,

>HEX DUP 9 > IF 7 + THEN [CHAR] 0 + ;
HI! $F0 AND 2/ 2/ 2/ 2/ >HEX TOKEN 3 + C! ;
LO! $0F AND >HEX TOKEN 4 + C! ;
>TOKEN DUP HI! LO! TOKEN ;
?EOF DUP 4 = IF CR ." End-of-file in comment" CR BYE THEN ;
$$2F PEEK [CHAR] * =
  IF SKIP
      BEGIN 
  	GETC ?EOF  [CHAR] * =
  	PEEK [CHAR] / =  AND
      UNTIL  SKIP
  ELSE  .WHERE ." Op_divide" CR THEN ;
$$22 .WHERE ." String " STRING "TYPE" CR ;
$$27 .WHERE GETC ?ESCAPE ." Integer " . [CHAR] ' EXPECT CR ;
$$04 .WHERE ." End_of_input" CR BYE ;
$$2D .WHERE ." Op_subtract" CR ;
$$2B .WHERE ." Op_add" CR ;
$$25 .WHERE ." Op_mod" CR ;
$$2A .WHERE ." Op_multiply" CR ;
$$7B .WHERE ." LeftBrace" CR ;
$$7D .WHERE ." RightBrace" CR ;
$$2C .WHERE ." Comma" CR ;
$$29 .WHERE ." RightParen" CR ;
$$28 .WHERE ." LeftParen" CR ;
$$3B .WHERE ." Semicolon" CR ;
$$3D .WHERE s" equal" s" assign" EQ ;
$$21 .WHERE s" notequal" s" not" EQ ;
$$3C .WHERE s" lessequal" s" less" EQ ;
$$3E .WHERE s" greaterequal" s" greater" EQ ;
$$26 .WHERE [CHAR] & EXPECT ." Op_and" CR ;
$$7C .WHERE [CHAR] | EXPECT ." Op_or" CR ;
$$20  ; \ space

CREATE KEYWORD 0 C, CHAR $ C, CHAR $ C, 5 CHARS ALLOT

>KEYWORD DUP 2 + KEYWORD C!
            KEYWORD 3 + SWAP CMOVE  KEYWORD ;
FIND-KW DUP 5 <=
  IF 2DUP >KEYWORD FIND
     IF TRUE 2SWAP 2DROP ELSE DROP FALSE THEN
  ELSE FALSE THEN ;
$$if ." Keyword_if" ;
$$else ." Keyword_else" ;
$$while ." Keyword_while" ;
$$print ." Keyword_print" ;
$$putc ." Keyword_putc" ;
DIGIT? 48 58 WITHIN ;
ALPHA? DUP 95 = SWAP \ underscore?
          DUP 97 123 WITHIN SWAP	  \ lower?
          65 91 WITHIN  OR OR ;	  \ upper?
ALNUM? DUP DIGIT? SWAP ALPHA? OR ;
INTEGER 0
  BEGIN  PEEK DIGIT?
  WHILE  GETC [CHAR] 0 -  SWAP 10 * +
  REPEAT ;
?INTEGER? CR ." Invalid number" CR BYE ;
?INTEGER PEEK ALPHA? IF ?INTEGER? THEN ;
DIGIT .WHERE+ ." Integer " INTEGER ?INTEGER . CR ;
NAME PAD
        BEGIN  PEEK ALNUM?

WHILE GETC OVER C! CHAR+ REPEAT PAD TUCK - ;

IDENT ." Identifier " TYPE ;
ALPHA .WHERE+ NAME FIND-KW
         IF EXECUTE ELSE IDENT THEN CR ;
?CHAR? CR ." Character '" EMIT ." ' not recognized" CR BYE ;
SPACE? DUP BL = SWAP 9 14 WITHIN OR ;
SKIP-SPACE BEGIN PEEK SPACE? WHILE SKIP REPEAT ;
CONSUME
  SKIP-SPACE
  PEEK DIGIT? IF DIGIT ELSE
   PEEK ALPHA? IF ALPHA ELSE
    PEEK >TOKEN FIND
    IF SKIP EXECUTE ELSE GETC ?CHAR? BYE THEN
  THEN THEN ;
TOKENIZE BEGIN CONSUME AGAIN ;

TOKENIZE</lang>

Output:

Tested against all programs in Compiler/Sample programs.

FreeBASIC

Tested with FreeBASIC 1.05 <lang FreeBASIC>enum Token_type

   tk_EOI
   tk_Mul
   tk_Div
   tk_Mod
   tk_Add
   tk_Sub
   tk_Negate
   tk_Not
   tk_Lss
   tk_Leq
   tk_Gtr
   tk_Geq
   tk_Eq
   tk_Neq
   tk_Assign
   tk_And
   tk_Or
   tk_If
   tk_Else
   tk_While
   tk_Print
   tk_Putc
   tk_Lparen
   tk_Rparen
   tk_Lbrace
   tk_Rbrace
   tk_Semi
   tk_Comma
   tk_Ident
   tk_Integer
   tk_String

end enum

const NewLine = chr(10) const DoubleQuote = chr(34) const BackSlash = chr(92)

' where we store keywords and variables type Symbol

   s_name as string
   tok as Token_type

end type

dim shared symtab() as Symbol

dim shared cur_line as string dim shared cur_ch as string dim shared line_num as integer dim shared col_num as integer

function is_digit(byval ch as string) as long

   is_digit = ch >= "0" AndAlso ch <= "9"

end function

function is_alnum(byval ch as string) as long

   is_alnum = (ucase(ch) >= "A" AndAlso ucase(ch) <= "Z") OrElse is_digit(ch)

end function

sub error_msg(byval eline as integer, byval ecol as integer, byval msg as string)

   print "("; eline; ":"; ecol; ") "; msg   
   print : print "Hit any to end program"   
   sleep                                    
   system

end sub

' add an identifier to the symbol table function install(byval s_name as string, byval tok as Token_type) as integer

   dim n as integer = ubound(symtab) + 1
   redim preserve symtab(n)
   symtab(n).s_name = s_name
   symtab(n).tok    = tok
   return n

end function

' search for an identifier in the symbol table function lookup(byval s_name as string) as integer

   dim i as integer
   for i = lbound(symtab) to ubound(symtab)
       if symtab(i).s_name = s_name then return i
   next
   return -1

end function

sub next_line() ' read the next line of input from the source file

   cur_line = ""
   cur_ch  = ""        ' empty cur_ch means end-of-file
   if eof(1) then exit sub
   line input #1, cur_line
   cur_line = cur_line + NewLine
   line_num += + 1
   col_num = 1

end sub

sub next_char() ' get the next char

   cur_ch = ""
   col_num += 1
   if col_num > len(cur_line) then next_line()
   if col_num <= len(cur_line) then cur_ch = mid(cur_line, col_num, 1)

end sub

function follow(byval err_line as integer, byval err_col as integer, byval expect as string, byval ifyes as Token_type, byval ifno as Token_type) as Token_type

   if cur_ch = expect then
       next_char()
       return ifyes
   end if
   if ifno = tk_eoi then error_msg(err_line, err_col, "follow unrecognized character: " + cur_ch)
   return ifno

end function

sub gettok(byref err_line as integer, byref err_col as integer, byref tok as Token_type, byref v as string)

   ' skip whitespace
   do while (cur_ch = " " or cur_ch = chr(9) or cur_ch = NewLine) and (cur_ch <> "")
       next_char()
   loop
   err_line = line_num
   err_col  = col_num
   select case cur_ch
       case "":  tok = tk_eoi: exit sub
       case "{": tok = tk_lbrace: next_char(): exit sub
       case "}": tok = tk_rbrace: next_char(): exit sub
       case "(": tok = tk_lparen: next_char(): exit sub
       case ")": tok = tk_rparen: next_char(): exit sub
       case "+": tok = tk_add:    next_char(): exit sub
       case "-": tok = tk_sub:    next_char(): exit sub
       case "*": tok = tk_mul:    next_char(): exit sub
       case "%": tok = tk_Mod:    next_char(): exit sub
       case ";": tok = tk_semi:   next_char(): exit sub
       case ",": tok = tk_comma:  next_char(): exit sub
       case "/": ' div or comment
           next_char()
           if cur_ch <> "*" then
               tok = tk_div
               exit sub
           end if
           ' skip comments
           next_char()
           do
               if cur_ch = "*" then
                   next_char()
                   if cur_ch = "/" then
                       next_char()
                       gettok(err_line, err_col, tok, v)
                       exit sub
                   end if
               elseif cur_ch = "" then error_msg(err_line, err_col, "EOF in comment")
               else
                   next_char()
               end if
           loop
       case "'":   ' single char literals
           next_char()
           v = str(asc(cur_ch))
           if cur_ch = "'" then error_msg(err_line, err_col, "empty character constant")
           if cur_ch = BackSlash then          
               next_char()
               if cur_ch = "n" then
                   v = "10"
               elseif cur_ch = BackSlash then  
                   v = "92"                  
               else error_msg(err_line, err_col, "unknown escape sequence: " + cur_ch)
               end if
           end if
           next_char()
           if cur_ch <> "'" then error_msg(err_line, err_col, "multi-character constant")
           next_char()
           tok = tk_integer
           exit sub
       case "<": next_char(): tok = follow(err_line, err_col, "=", tk_Leq, tk_Lss): exit sub
       case ">": next_char(): tok = follow(err_line, err_col, "=", tk_Geq, tk_Gtr): exit sub
       case "!": next_char(): tok = follow(err_line, err_col, "=", tk_Neq, tk_Not): exit sub
       case "=": next_char(): tok = follow(err_line, err_col, "=", tk_Eq,  tk_Assign): exit sub
       case "&": next_char(): tok = follow(err_line, err_col, "&", tk_And, tk_EOI): exit sub
       case "|": next_char(): tok = follow(err_line, err_col, "|", tk_Or,  tk_EOI): exit sub
       case DoubleQuote: ' string
           v = cur_ch
           next_char()
           do while cur_ch <> DoubleQuote
               if cur_ch = NewLine then error_msg(err_line, err_col, "EOL in string")
               if cur_ch = "" then error_msg(err_line, err_col, "EOF in string")
               v += cur_ch
               next_char()
           loop
           v += cur_ch
           next_char()
           tok = tk_string
           exit sub
       case else   ' integers or identifiers
           dim is_number as boolean = is_digit(cur_ch)
           v = ""
           do while is_alnum(cur_ch) orelse cur_ch = "_"
               if not is_digit(cur_ch) then is_number = false
               v += cur_ch
               next_char()
           loop
           if len(v) = 0 then error_msg(err_line, err_col, "unknown character: " + cur_ch)
           if is_digit(mid(v, 1, 1)) then
               if not is_number then error_msg(err_line, err_col, "invalid number: " + v)
               tok = tk_integer
               exit sub
           end if
           dim as integer index = lookup(v)
           if index = -1 then
               tok = tk_ident
           else
               tok = symtab(index).tok
           end if
           exit sub
   end select

end sub

sub init_lex(byval filein as string)

   install("else",  tk_else)
   install("if",    tk_if)
   install("print", tk_print)
   install("putc",  tk_putc)
   install("while", tk_while)
   open filein for input as #1
   cur_line = ""
   line_num = 0
   col_num = 0
   next_char()

end sub

sub scanner()

   dim err_line as integer
   dim err_col as integer
   dim tok as Token_type
   dim v as string
   dim tok_list(tk_eoi to tk_string) as string
   tok_list(tk_EOI    ) = "End_of_input"
   tok_list(tk_Mul    ) = "Op_multiply"
   tok_list(tk_Div    ) = "Op_divide"
   tok_list(tk_Mod    ) = "Op_mod"
   tok_list(tk_Add    ) = "Op_add"
   tok_list(tk_Sub    ) = "Op_subtract"
   tok_list(tk_Negate ) = "Op_negate"
   tok_list(tk_Not    ) = "Op_not"
   tok_list(tk_Lss    ) = "Op_less"
   tok_list(tk_Leq    ) = "Op_lessequal"
   tok_list(tk_Gtr    ) = "Op_greater"
   tok_list(tk_Geq    ) = "Op_greaterequal"
   tok_list(tk_Eq     ) = "Op_equal"
   tok_list(tk_Neq    ) = "Op_notequal"
   tok_list(tk_Assign ) = "Op_assign"
   tok_list(tk_And    ) = "Op_and"
   tok_list(tk_Or     ) = "Op_or"
   tok_list(tk_If     ) = "Keyword_if"
   tok_list(tk_Else   ) = "Keyword_else"
   tok_list(tk_While  ) = "Keyword_while"
   tok_list(tk_Print  ) = "Keyword_print"
   tok_list(tk_Putc   ) = "Keyword_putc"
   tok_list(tk_Lparen ) = "LeftParen"
   tok_list(tk_Rparen ) = "RightParen"
   tok_list(tk_Lbrace ) = "LeftBrace"
   tok_list(tk_Rbrace ) = "RightBrace"
   tok_list(tk_Semi   ) = "Semicolon"
   tok_list(tk_Comma  ) = "Comma"
   tok_list(tk_Ident  ) = "Identifier"
   tok_list(tk_Integer) = "Integer"
   tok_list(tk_String ) = "String"
   do
       gettok(err_line, err_col, tok, v)
       print using "#####  ##### \               " + BackSlash; err_line; err_col; tok_list(tok);
       if tok = tk_integer orelse tok = tk_ident orelse tok = tk_string then print " " + v;
       print
   loop until tok = tk_eoi

end sub

sub main()

   if command(1) = "" then print "filename required" : exit sub   
   init_lex(command(1))
   scanner()

end sub

main() print : print "Hit any to end program" sleep system</lang>

Output  —  test case 3:

    5     16 Keyword_print
    5     40 Op_subtract
    6     16 Keyword_putc
    6     40 Op_less
    7     16 Keyword_if
    7     40 Op_greater
    8     16 Keyword_else
    8     40 Op_lessequal
    9     16 Keyword_while
    9     40 Op_greaterequal
   10     16 LeftBrace
   10     40 Op_equal
   11     16 RightBrace
   11     40 Op_notequal
   12     16 LeftParen
   12     40 Op_and
   13     16 RightParen
   13     40 Op_or
   14     16 Op_subtract
   14     40 Semicolon
   15     16 Op_not
   15     40 Comma
   16     16 Op_multiply
   16     40 Op_assign
   17     16 Op_divide
   17     40 Integer           42
   18     16 Op_mod
   18     40 String            "String literal"
   19     16 Op_add
   19     40 Identifier        variable_name
   20     26 Integer           10
   21     26 Integer           92
   22     26 Integer           32
   22     30 End_of_input

Java

<lang java> // Translated from python source

import java.io.File; import java.io.FileNotFoundException; import java.util.HashMap; import java.util.Map; import java.util.Scanner;

public class Lexer {

   private int line;
   private int pos;
   private int position;
   private char chr;
   private String s;
   
   Map<String, TokenType> keywords = new HashMap<>();
   
   static class Token {
       public TokenType tokentype;
       public String value;
       public int line;
       public int pos;
       Token(TokenType token, String value, int line, int pos) {
           this.tokentype = token; this.value = value; this.line = line; this.pos = pos;
       }
       @Override
       public String toString() {
           String result = String.format("%5d  %5d %-15s", this.line, this.pos, this.tokentype);
           switch (this.tokentype) {
               case Integer:
                   result += String.format("  %4s", value);
                   break;
               case Identifier:
                   result += String.format(" %s", value);
                   break;
               case String:
                   result += String.format(" \"%s\"", value);
                   break;
           }
           return result;
       }
   }
   
   static enum TokenType {
       End_of_input, Op_multiply,  Op_divide, Op_mod, Op_add, Op_subtract,
       Op_negate, Op_not, Op_less, Op_lessequal, Op_greater, Op_greaterequal,
       Op_equal, Op_notequal, Op_assign, Op_and, Op_or, Keyword_if,
       Keyword_else, Keyword_while, Keyword_print, Keyword_putc, LeftParen, RightParen,
       LeftBrace, RightBrace, Semicolon, Comma, Identifier, Integer, String
   }
   
   static void error(int line, int pos, String msg) {
       if (line > 0 && pos > 0) {
           System.out.printf("%s in line %d, pos %d\n", msg, line, pos);
       } else {
           System.out.println(msg);
       }
       System.exit(1);
   }
   Lexer(String source) {
       this.line = 1;
       this.pos = 0;
       this.position = 0;
       this.s = source;
       this.chr = this.s.charAt(0);
       this.keywords.put("if", TokenType.Keyword_if);
       this.keywords.put("else", TokenType.Keyword_else);
       this.keywords.put("print", TokenType.Keyword_print);
       this.keywords.put("putc", TokenType.Keyword_putc);
       this.keywords.put("while", TokenType.Keyword_while);
       
   }
   Token follow(char expect, TokenType ifyes, TokenType ifno, int line, int pos) {
       if (getNextChar() == expect) {
           getNextChar();
           return new Token(ifyes, "", line, pos);
       }
       if (ifno == TokenType.End_of_input) {
           error(line, pos, String.format("follow: unrecognized character: (%d) '%c'", (int)this.chr, this.chr));
       }
       return new Token(ifno, "", line, pos);
   }
   Token char_lit(int line, int pos) {
       char c = getNextChar(); // skip opening quote
       int n = 0;
       if (c == '\) {
           error(line, pos, "empty character constant");
       } else if (c == '\\') {
           c = getNextChar();
           if (c == 'n') {
               n = 10;
           } else if (c == '\\') {
               n = '\\';
           } else {
               error(line, pos, String.format("unknown escape sequence \\%c", c));
           }
       }
       if (getNextChar() != '\) {
           error(line, pos, "multi-character constant");
       }
       getNextChar();
       return new Token(TokenType.Integer, "" + n, line, pos);
   }
   Token string_lit(char start, int line, int pos) {
       String result = "";
       while (getNextChar() != start) {
           if (this.chr == '\u0000') {
               error(line, pos, "EOF while scanning string literal");
           }
           if (this.chr == '\n') {
               error(line, pos, "EOL while scanning string literal");
           }
           result += this.chr;
       }
       getNextChar();
       return new Token(TokenType.String, result, line, pos);
   }
   Token div_or_comment(int line, int pos) {
       if (getNextChar() != '*') {
           return new Token(TokenType.Op_divide, "", line, pos);
       }
       getNextChar();
       while (true) { 
           if (this.chr == '\u0000') {
               error(line, pos, "EOF in comment");
           } else if (this.chr == '*') {
               if (getNextChar() == '/') {
                   getNextChar();
                   return getToken();
               }
           } else {
               getNextChar();
           }
       }
   }
   Token identifier_or_integer(int line, int pos) {
       boolean is_number = true;
       String text = "";
       
       while (Character.isAlphabetic(this.chr) || Character.isDigit(this.chr)) {
           text += this.chr;
           if (!Character.isDigit(this.chr)) {
               is_number = false;
           }
           getNextChar();
       }
       
       if (text.equals("")) {
           error(line, pos, String.format("identifer_or_integer unrecopgnized character: (%d) %c", (int)this.chr, this.chr));
       }
       
       if (Character.isDigit(text.charAt(0))) {
           if (!is_number) {
               error(line, pos, String.format("invaslid number: %s", text));
           }
           return new Token(TokenType.Integer, text, line, pos);
       }
       
       if (this.keywords.containsKey(text)) {
           return new Token(this.keywords.get(text), "", line, pos);
       }
       return new Token(TokenType.Identifier, text, line, pos);
   }
   Token getToken() {
       int line, pos;
       while (Character.isWhitespace(this.chr)) {
           getNextChar();
       }
       line = this.line;
       pos = this.pos;
       
       switch (this.chr) {
           case '\u0000': return new Token(TokenType.End_of_input, "", this.line, this.pos);
           case '/': return div_or_comment(line, pos);
           case '\: return char_lit(line, pos);
           case '<': return follow('=', TokenType.Op_lessequal, TokenType.Op_less, line, pos);
           case '>': return follow('=', TokenType.Op_greaterequal, TokenType.Op_greater, line, pos);
           case '=': return follow('=', TokenType.Op_equal, TokenType.Op_assign, line, pos);
           case '!': return follow('=', TokenType.Op_not, TokenType.Op_notequal, line, pos);
           case '&': return follow('&', TokenType.Op_and, TokenType.End_of_input, line, pos);
           case '|': return follow('|', TokenType.Op_or, TokenType.End_of_input, line, pos);
           case '"': return string_lit(this.chr, line, pos);
           case '{': getNextChar(); return new Token(TokenType.LeftBrace, "", line, pos);
           case '}': getNextChar(); return new Token(TokenType.RightBrace, "", line, pos);
           case '(': getNextChar(); return new Token(TokenType.LeftParen, "", line, pos);
           case ')': getNextChar(); return new Token(TokenType.RightParen, "", line, pos);
           case '+': getNextChar(); return new Token(TokenType.Op_add, "", line, pos);
           case '-': getNextChar(); return new Token(TokenType.Op_subtract, "", line, pos);
           case '*': getNextChar(); return new Token(TokenType.Op_multiply, "", line, pos);
           case '%': getNextChar(); return new Token(TokenType.Op_mod, "", line, pos);
           case ';': getNextChar(); return new Token(TokenType.Semicolon, "", line, pos);
           case ',': getNextChar(); return new Token(TokenType.Comma, "", line, pos);
           
           default: return identifier_or_integer(line, pos);
       }
   }
   
   char getNextChar() {
       this.pos++;
       this.position++;
       if (this.position >= this.s.length()) {
           this.chr = '\u0000';
           return this.chr;
       }
       this.chr = this.s.charAt(this.position);
       if (this.chr == '\n') {
           this.line++;
           this.pos = 0;
       }
       return this.chr;
   }
   void printTokens() {
       Token t;
       while ((t = getToken()).tokentype != TokenType.End_of_input) {
           System.out.println(t);
       }
       System.out.println(t);
   }
   public static void main(String[] args) {
       if (args.length > 0) {
           try {
               
               File f = new File(args[0]);
               Scanner s = new Scanner(f);
               String source = " ";
               while (s.hasNext()) {
                   source += s.nextLine() + "\n";
               }
               Lexer l = new Lexer(source);
               l.printTokens();
           } catch(FileNotFoundException e) {
               error(-1, -1, "Exception: " + e.getMessage());
           }
       } else {
           error(-1, -1, "No args");
       }
   }

} </lang>

Julia

<lang julia>struct Tokenized

   startline::Int
   startcol::Int
   name::String
   value::Union{Nothing, Int, String}

end

const optokens = Dict("*" => "Op_multiply", "/" => "Op_divide", "%" => "Op_mod", "+" => "Op_add",

                     "-" => "Op_subtract", "!" => "Op_not", "<" => "Op_less", "<=" => "Op_lessequal",
                     ">" => "Op_greater", ">=" => "Op_greaterequal", "==" => "Op_equal", "!=" => "Op_notequal",
                     "!" => "Op_not", "=" => "Op_assign", "&&" => "Op_and", "||" => "Op_or")

const keywordtokens = Dict("if" => "Keyword_if", "else" => "Keyword_else", "while" => "Keyword_while",

                          "print" => "Keyword_print", "putc" => "Keyword_putc")

const symboltokens = Dict("(" => "LeftParen", ")" => "RightParen", "{" => "LeftBrace",

                         "}" => "RightBrace", ";" => "Semicolon", "," => "Comma")

const errors = ["Empty character constant.", "Unknown escape sequence.", "Multi-character constant.",

               "End-of-file in comment. Closing comment characters not found.",
               "End-of-file while scanning string literal. Closing string character not found.",
               "End-of-line while scanning string literal. Closing string character not found before end-of-line.",
               "Unrecognized character.", "Invalid number. Starts like a number, but ends in non-numeric characters."]

asws(s) = (nnl = length(findall(x->x=='\n', s)); " " ^ (length(s) - nnl) * "\n" ^ nnl) comment2ws(t) = (while occursin("/*", t) t = replace(t, r"\/\* .+? (?: \*\/)"xs => asws; count = 1) end; t) hasinvalidescapes(t) = ((m = match(r"\\.", t)) != nothing && m.match != "\\\\" && m.match != "\\n") hasemptycharconstant(t) = (match(r"\'\'", t) != nothing) hasmulticharconstant(t) = ((m = match(r"\'[^\'][^\']+\'", t)) != nothing && m.match != "\'\\\\\'" && m.match != "\'\\n\'") hasunbalancedquotes(t) = isodd(length(findall(x -> x == '\"', t))) hasunrecognizedchar(t) = match(r"[^\w\s\d\*\/\%\+\-\<\>\=\!\&\|\(\)\{\}\;\,\"\'\\]", t) != nothing

function throwiferror(line, n)

   if hasemptycharconstant(line)
       throw("Tokenizer error line $n: " * errors[1])
   end
   if hasinvalidescapes(line)
       throw("Tokenizer error line $n: " * errors[2])
   end
   if hasmulticharconstant(line)
   println("error at ", match(r"\'[^\'][^\']+\'", line).match)
       throw("Tokenizer error line $n: " * errors[3])
   end
   if occursin("/*", line)
       throw("Tokenizer error line $n: " * errors[4])
   end
   if hasunrecognizedchar(line)
       throw("Tokenizer error line $n: " * errors[7])
   end

end

function tokenize(txt)

   tokens = Vector{Tokenized}()
   txt = comment2ws(txt)
   lines = split(txt, "\n")
   if hasunbalancedquotes(txt)
       throw("Tokenizer error: $(errors[5])")
   end
   for (startline, line) in enumerate(lines)
       if strip(line) == ""
           continue
       end
       throwiferror(line, startline)
       lastc = Char(0)
       withintoken = 0
       for (startcol, c) in enumerate(line)
           if withintoken > 0
               withintoken -= 1
               continue
           elseif isspace(c[1])
               continue
           elseif (c == '=') && (startcol > 1) && ((c2 = line[startcol - 1]) in ['<', '>', '=', '!'])
                   tokens[end] = Tokenized(startline, startcol - 1, optokens[c2 * c], nothing)
           elseif (c == '&') || (c == '|')
               if length(line) > startcol && line[startcol + 1] == c
                   push!(tokens, Tokenized(startline, startcol, optokens[c * c], nothing))
                   withintoken = 1
               else
                   throw("Tokenizer error line $startline: $(errors[7])")
               end
           elseif haskey(optokens, string(c))
               push!(tokens, Tokenized(startline, startcol, optokens[string(c)], nothing))
           elseif haskey(symboltokens, string(c))
               push!(tokens, Tokenized(startline, startcol, symboltokens[string(c)], nothing))
           elseif isdigit(c)
               integerstring = match(r"^\d+", line[startcol:end]).match
               pastnumposition = startcol + length(integerstring)
               if (pastnumposition <= length(line)) && isletter(line[pastnumposition])
                   throw("Tokenizer error line $startline: " * errors[8])
               end
               i = parse(Int, integerstring)
               push!(tokens, Tokenized(startline, startcol, "Integer", i))
               withintoken = length(integerstring) - 1
           elseif c == Char(39)  # single quote
               if (m = match(r"([^\\\'\n]|\\n|\\\\)\'", line[startcol+1:end])) != nothing
                   chs = m.captures[1]
                   i = (chs == "\\n") ? Int('\n') : (chs == "\\\\" ? Int('\\') : Int(chs[1]))
                   push!(tokens, Tokenized(startline, startcol, "Integer", i))
                   withintoken = length(chs) + 1
               else
                   println("line $startline: bad match with ", line[startcol+1:end])
               end
           elseif c == Char(34)  # double quote
               if (m = match(r"([^\"\n]+)\"", line[startcol+1:end])) == nothing
                   throw("Tokenizer error line $startline: $(errors[6])")
               end
               litstring = m.captures[1]
               push!(tokens, Tokenized(startline, startcol, "String", "\"$litstring\""))
               withintoken = length(litstring) + 1
           elseif (cols = findfirst(r"[a-zA-Z]+", line[startcol:end])) != nothing
               litstring = line[cols .+ startcol .- 1]
               if haskey(keywordtokens, string(litstring))
                   push!(tokens, Tokenized(startline, startcol, keywordtokens[litstring], nothing))
               else
                   litstring = match(r"[_a-zA-Z0-9]+", line[startcol:end]).match
                   push!(tokens, Tokenized(startline, startcol, "Identifier", string(litstring)))
               end
               withintoken = length(litstring) - 1
           end
           lastc = c
       end
   end
   push!(tokens, Tokenized(length(lines), length(lines[end]) + 1, "End_of_input", nothing))
   tokens

end

const test3txt = raw""" /*

 All lexical tokens - not syntactically correct, but that will
 have to wait until syntax analysis
*/

/* Print */ print /* Sub */ - /* Putc */ putc /* Lss */ < /* If */ if /* Gtr */ > /* Else */ else /* Leq */ <= /* While */ while /* Geq */ >= /* Lbrace */ { /* Eq */ == /* Rbrace */ } /* Neq */  != /* Lparen */ ( /* And */ && /* Rparen */ ) /* Or */ || /* Uminus */ - /* Semi */  ; /* Not */  ! /* Comma */ , /* Mul */ * /* Assign */ = /* Div */ / /* Integer */ 42 /* Mod */  % /* String */ "String literal" /* Add */ + /* Ident */ variable_name /* character literal */ '\n' /* character literal */ '\\' /* character literal */ ' ' """

println("Line Col Name Value") for tok in tokenize(test3txt)

   println(lpad(tok.startline, 3), lpad(tok.startcol, 5), lpad(tok.name, 18), "  ", tok.value != nothing ? tok.value : "")

end

</lang>

Output:

Line Col Name Value

 5   16     Keyword_print
 5   40       Op_subtract
 6   16      Keyword_putc
 6   40           Op_less
 7   16        Keyword_if
 7   40        Op_greater
 8   16      Keyword_else
 8   40      Op_lessequal
 9   16     Keyword_while
 9   40   Op_greaterequal
10   16         LeftBrace
10   40          Op_equal
11   16        RightBrace
11   40       Op_notequal
12   16         LeftParen
12   40            Op_and
13   16        RightParen
13   40             Op_or
14   16       Op_subtract
14   40         Semicolon
15   16            Op_not
15   40             Comma
16   16       Op_multiply
16   40         Op_assign
17   16         Op_divide
17   40           Integer  42
18   16            Op_mod
18   40            String  "String literal"
19   16            Op_add
19   40        Identifier  variable_name
20   26           Integer  10
21   26           Integer  92
22   26           Integer  32
23    1      End_of_input

Go

Translation of: FreeBASIC

<lang go>package main

import (

   "bufio"
   "fmt"
   "log"
   "os"

)

type TokenType int

const (

   tkEOI TokenType = iota
   tkMul
   tkDiv
   tkMod
   tkAdd
   tkSub
   tkNegate
   tkNot
   tkLss
   tkLeq
   tkGtr
   tkGeq
   tkEq
   tkNeq
   tkAssign
   tkAnd
   tkOr
   tkIf
   tkElse
   tkWhile
   tkPrint
   tkPutc
   tkLparen
   tkRparen
   tkLbrace
   tkRbrace
   tkSemi
   tkComma
   tkIdent
   tkInteger
   tkString

)

type Symbol struct {

   name string
   tok  TokenType

}

// symbol table var symtab []Symbol

var scanner *bufio.Scanner

var (

   curLine = ""
   curCh   byte
   lineNum = 0
   colNum  = 0

)

const etx byte = 4 // used to signify EOI

func isDigit(ch byte) bool {

   return ch >= '0' && ch <= '9'

}

func isAlnum(ch byte) bool {

   return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || isDigit(ch)

}

func errorMsg(eline, ecol int, msg string) {

   log.Fatalf("(%d:%d) %s", eline, ecol, msg)

}

// add an identifier to the symbol table func install(name string, tok TokenType) {

   sym := Symbol{name, tok}
   symtab = append(symtab, sym)

}

// search for an identifier in the symbol table func lookup(name string) int {

   for i := 0; i < len(symtab); i++ {
       if symtab[i].name == name {
           return i
       }
   }
   return -1

}

// read the next line of input from the source file func nextLine() {

   if scanner.Scan() {
       curLine = scanner.Text()
       lineNum++
       colNum = 0
       if curLine == "" { // skip blank lines
           nextLine()
       }
   } else {
       err := scanner.Err()
       if err == nil { // EOF
           curCh = etx
           curLine = ""
           lineNum++
           colNum = 1
       } else {
           log.Fatal(err)
       }
   }

}

// get the next char func nextChar() {

   if colNum >= len(curLine) {
       nextLine()
   }
   if colNum < len(curLine) {
       curCh = curLine[colNum]
       colNum++
   }

}

func follow(eline, ecol int, expect byte, ifyes, ifno TokenType) TokenType {

   if curCh == expect {
       nextChar()
       return ifyes
   }
   if ifno == tkEOI {
       errorMsg(eline, ecol, "follow unrecognized character: "+string(curCh))
   }
   return ifno

}

func gettok() (eline, ecol int, tok TokenType, v string) {

   // skip whitespace
   for curCh == ' ' || curCh == '\t' || curCh == '\n' {
       nextChar()
   }
   eline = lineNum
   ecol = colNum
   switch curCh {
   case etx:
       tok = tkEOI
       return
   case '{':
       tok = tkLbrace
       nextChar()
       return
   case '}':
       tok = tkRbrace
       nextChar()
       return
   case '(':
       tok = tkLparen
       nextChar()
       return
   case ')':
       tok = tkRparen
       nextChar()
       return
   case '+':
       tok = tkAdd
       nextChar()
       return
   case '-':
       tok = tkSub
       nextChar()
       return
   case '*':
       tok = tkMul
       nextChar()
       return
   case '%':
       tok = tkMod
       nextChar()
       return
   case ';':
       tok = tkSemi
       nextChar()
       return
   case ',':
       tok = tkComma
       nextChar()
       return
   case '/': // div or comment
       nextChar()
       if curCh != '*' {
           tok = tkDiv
           return
       }
       // skip comments
       nextChar()
       for {
           if curCh == '*' {
               nextChar()
               if curCh == '/' {
                   nextChar()
                   eline, ecol, tok, v = gettok()
                   return
               }
           } else if curCh == etx {
               errorMsg(eline, ecol, "EOF in comment")
           } else {
               nextChar()
           }
       }
   case '\: // single char literals
       nextChar()
       v = fmt.Sprintf("%d", curCh)
       if curCh == '\ {
           errorMsg(eline, ecol, "Empty character constant")
       }
       if curCh == '\\' {
           nextChar()
           if curCh == 'n' {
               v = "10"
           } else if curCh == '\\' {
               v = "92"
           } else {
               errorMsg(eline, ecol, "unknown escape sequence: "+string(curCh))
           }
       }
       nextChar()
       if curCh != '\ {
           errorMsg(eline, ecol, "multi-character constant")
       }
       nextChar()
       tok = tkInteger
       return
   case '<':
       nextChar()
       tok = follow(eline, ecol, '=', tkLeq, tkLss)
       return
   case '>':
       nextChar()
       tok = follow(eline, ecol, '=', tkGeq, tkGtr)
       return
   case '!':
       nextChar()
       tok = follow(eline, ecol, '=', tkNeq, tkNot)
       return
   case '=':
       nextChar()
       tok = follow(eline, ecol, '=', tkEq, tkAssign)
       return
   case '&':
       nextChar()
       tok = follow(eline, ecol, '&', tkAnd, tkEOI)
       return
   case '|':
       nextChar()
       tok = follow(eline, ecol, '|', tkOr, tkEOI)
       return
   case '"': // string
       v = string(curCh)
       nextChar()
       for curCh != '"' {
           if curCh == '\n' {
               errorMsg(eline, ecol, "EOL in string")
           }
           if curCh == etx {
               errorMsg(eline, ecol, "EOF in string")
           }
           v += string(curCh)
           nextChar()
       }
       v += string(curCh)
       nextChar()
       tok = tkString
       return
   default: // integers or identifiers
       isNumber := isDigit(curCh)
       v = ""
       for isAlnum(curCh) || curCh == '_' {
           if !isDigit(curCh) {
               isNumber = false
           }
           v += string(curCh)
           nextChar()
       }
       if len(v) == 0 {
           errorMsg(eline, ecol, "unknown character: "+string(curCh))
       }
       if isDigit(v[0]) {
           if !isNumber {
               errorMsg(eline, ecol, "invalid number: "+string(curCh))
           }
           tok = tkInteger
           return
       }
       index := lookup(v)
       if index == -1 {
           tok = tkIdent
       } else {
           tok = symtab[index].tok
       }
       return
   }

}

func initLex() {

   install("else", tkElse)
   install("if", tkIf)
   install("print", tkPrint)
   install("putc", tkPutc)
   install("while", tkWhile)
   nextChar()

}

func process() {

   tokMap := make(map[TokenType]string)
   tokMap[tkEOI] = "End_of_input"
   tokMap[tkMul] = "Op_multiply"
   tokMap[tkDiv] = "Op_divide"
   tokMap[tkMod] = "Op_mod"
   tokMap[tkAdd] = "Op_add"
   tokMap[tkSub] = "Op_subtract"
   tokMap[tkNegate] = "Op_negate"
   tokMap[tkNot] = "Op_not"
   tokMap[tkLss] = "Op_less"
   tokMap[tkLeq] = "Op_lessequal"
   tokMap[tkGtr] = "Op_greater"
   tokMap[tkGeq] = "Op_greaterequal"
   tokMap[tkEq] = "Op_equal"
   tokMap[tkNeq] = "Op_notequal"
   tokMap[tkAssign] = "Op_assign"
   tokMap[tkAnd] = "Op_and"
   tokMap[tkOr] = "Op_or"
   tokMap[tkIf] = "Keyword_if"
   tokMap[tkElse] = "Keyword_else"
   tokMap[tkWhile] = "Keyword_while"
   tokMap[tkPrint] = "Keyword_print"
   tokMap[tkPutc] = "Keyword_putc"
   tokMap[tkLparen] = "LeftParen"
   tokMap[tkRparen] = "RightParen"
   tokMap[tkLbrace] = "LeftBrace"
   tokMap[tkRbrace] = "RightBrace"
   tokMap[tkSemi] = "Semicolon"
   tokMap[tkComma] = "Comma"
   tokMap[tkIdent] = "Identifier"
   tokMap[tkInteger] = "Integer"
   tokMap[tkString] = "String"
   for {
       eline, ecol, tok, v := gettok()
       fmt.Printf("%5d  %5d %-16s", eline, ecol, tokMap[tok])
       if tok == tkInteger || tok == tkIdent || tok == tkString {
           fmt.Println(v)
       } else {
           fmt.Println()
       }
       if tok == tkEOI {
           return
       }
   }

}

func check(err error) {

   if err != nil {
       log.Fatal(err)
   }

}

func main() {

   if len(os.Args) < 2 {
       fmt.Println("Filename required")
       return
   }
   f, err := os.Open(os.Args[1])
   check(err)
   defer f.Close()
   scanner = bufio.NewScanner(f)
   initLex()
   process()

}</lang>

Output:

Test Case 3:

    5     16 Keyword_print   
    5     40 Op_subtract     
    6     16 Keyword_putc    
    6     40 Op_less         
    7     16 Keyword_if      
    7     40 Op_greater      
    8     16 Keyword_else    
    8     40 Op_lessequal    
    9     16 Keyword_while   
    9     40 Op_greaterequal 
   10     16 LeftBrace       
   10     40 Op_equal        
   11     16 RightBrace      
   11     40 Op_notequal     
   12     16 LeftParen       
   12     40 Op_and          
   13     16 RightParen      
   13     40 Op_or           
   14     16 Op_subtract     
   14     40 Semicolon       
   15     16 Op_not          
   15     40 Comma           
   16     16 Op_multiply     
   16     40 Op_assign       
   17     16 Op_divide       
   17     40 Integer         42
   18     16 Op_mod          
   18     40 String          "String literal"
   19     16 Op_add          
   19     40 Identifier      variable_name
   20     26 Integer         10
   21     26 Integer         92
   22     26 Integer         32
   23      1 End_of_input    

M2000 Interpreter

<lang M2000 Interpreter> Module lexical_analyzer { a$={/* All lexical tokens - not syntactically correct, but that will have to wait until syntax analysis */ /* Print */ print /* Sub */ - /* Putc */ putc /* Lss */ < /* If */ if /* Gtr */ > /* Else */ else /* Leq */ <= /* While */ while /* Geq */ >= /* Lbrace */ { /* Eq */ == /* Rbrace */ } /* Neq */  != /* Lparen */ ( /* And */ && /* Rparen */ ) /* Or */ || /* Uminus */ - /* Semi */  ; /* Not */  ! /* Comma */ , /* Mul */ * /* Assign */ = /* Div */ / /* Integer */ 42 /* Mod */  % /* String */ "String literal" /* Add */ + /* Ident */ variable_name /* character literal */ '\n' /* character literal */ '\\' /* character literal */ ' ' } lim=Len(a$) LineNo=1 ColumnNo=1 Document Output$ Buffer Scanner as Integer*lim Return Scanner, 0:=a$ offset=0 buffer1$="" flag_rem=true Ahead=lambda Scanner (a$, offset)->{ =false Try { \\ second parameter is the offset in buffer units \\ third parameter is length in bytes =Eval$(Scanner, offset,2*len(a$))=a$ } } Ahead2=lambda Scanner (a$, offset)->{ =false Try { =Eval$(Scanner, offset,2) ~ a$ } } const nl$=chr$(13)+chr$(10), quo$="""", er$="@", Ansi=3 Try { Do If Ahead("/*", offset) Then { offset+=2 : ColumnNo+=2 While not Ahead("*/", offset) If Ahead(nl$, offset) Then lineNo++: ColumnNo=1 : offset+=2 Else offset++ : ColumnNo++ End If if offset>lim then Error "End-of-file in comment. Closing comment characters not found"+er$ End if End While offset+=2 : ColumnNo+=2 } Else.if Ahead(nl$, offset) Then{ LineNo++: ColumnNo=1 offset+=2 } Else.if Ahead(quo$, offset) Then { Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo) offset++ : ColumnNo++ strin=offset While not Ahead(quo$, offset) If Ahead("/", offset) Then offset+=2 : ColumnNo+=2 else offset++ : ColumnNo++ End if checkerror() End While Output$="String "+quote$(Eval$(Scanner, strin, (offset-strin)*2))+nl$ offset++ : ColumnNo++ } Else.if Ahead("'", offset) Then { Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo) offset++ : ColumnNo++ strin=offset While not Ahead("'", offset) If Ahead("/", offset) Then offset+=2 : ColumnNo+=2 else offset++ : ColumnNo++ End if checkerror() End While lit$=format$(Eval$(Scanner, strin, (offset-strin)*2)) select case len(lit$) case 1 Output$="Integer "+str$(asc(lit$),0)+nl$ case >1 {Error "Multi-character constant."+er$} case 0 {Error "Empty character constant."+er$} end select offset++ : ColumnNo++ } Else.if Ahead2("[a-z]", offset) Then { strin=offset Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo) offset++ : ColumnNo++ While Ahead2("[a-zA-Z0-9_]", offset) offset++ : ColumnNo++ End While Keywords(Eval$(Scanner, strin, (offset-strin)*2)) } Else.if Ahead2("[0-9]", offset) Then { strin=offset Output$=format$("{0::-10}{1::-10} Integer ", LineNo, ColumnNo) offset++ : ColumnNo++ While Ahead2("[0-9]", offset) offset++ : ColumnNo++ End While if Ahead2("[a-zA-Z_]", offset) then {Error " Invalid number. Starts like a number, but ends in non-numeric characters."+er$} else Output$=Eval$(Scanner, strin, (offset-strin)*2)+nl$ end if } Else { Symbols(Eval$(Scanner, Offset, 2)) offset++ : ColumnNo++ } Until offset>=lim } er1$=leftpart$(error$,er$) if er1$<>"" then Print Report "Error:"+er1$ Output$="(Error)"+nl$+"Error:"+er1$ else Output$=format$("{0::-10}{1::-10}", LineNo, ColumnNo)+" End_of_Input"+nl$ end if Clipboard Output$ Save.Doc Output$, "lex.t", Ansi document lex$ Load.Doc lex$,"lex.t", Ansi Report lex$

Sub Keywords(a$) select case a$ case "if" a$="Keyword_if" case "else" a$="Keyword_else" case "while" a$="Keyword_while" case "print" a$="Keyword_print" case "putc" a$="Keyword_putc" else case a$="Identifier "+a$ end select Output$=a$+nl$ End sub Sub Symbols(a$) select case a$ case " ", chr$(9) a$="" case "(" a$="LeftParen" case ")" a$="RightParen" case "{" a$="LeftBrace" case "}" a$="RightBrace" case ";" a$="Semicolon" case "," a$="Comma" case "*" a$="Op_multiply" case "/" a$="Op_divide" case "+" a$="Op_add" case "-" a$="Op_subtract" case "%" a$="Op_mod" case "<" { if Ahead("=", offset+1) Then offset++ a$="Op_lessequal" ColumnNo++ else a$="Op_less" end if } case ">" { if Ahead("=", offset+1) Then offset++ ColumnNo++ a$="Op_greaterequal" else a$="Op_greater" end if } case "=" { if Ahead("=", offset+1) Then offset++ ColumnNo++ a$="Op_equal" else a$="Op_assign" end if } case "!" { if Ahead("=", offset+1) Then offset++ ColumnNo++ a$="Op_notequal" else a$="Op_not" end if } case "&" { if Ahead("&", offset+1) Then offset++ ColumnNo++ a$="Op_and" else a$="" end if } case "|" { if Ahead("|", offset+1) Then offset++ ColumnNo++ a$="Op_or" else a$="" end if } else case {Error "Unrecognized character."+er$} end select if a$<>"" then Output$=format$("{0::-10}{1::-10} ", LineNo, ColumnNo)+a$+nl$ end if End Sub Sub checkerror() if offset>lim then { Error "End-of-line while scanning string literal. Closing string character not found before end-of-line."+er$ } else.if Ahead(nl$,offset) then { Error "End-of-file while scanning string literal. Closing string character not found."+er$ } End Sub } lexical_analyzer </lang>

Output:
         5        16 Keyword_print
         5        40 Op_subtract
         6        16 Keyword_putc
         6        40 Op_less
         7        16 Keyword_if
         7        40 Op_greater
         8        16 Keyword_else
         8        41 Op_lessequal
         9        16 Keyword_while
         9        41 Op_greaterequal
        10        16 LeftBrace
        10        41 Op_equal
        11        16 RightBrace
        11        41 Op_notequal
        12        16 LeftParen
        12        41 Op_and
        13        16 RightParen
        14        16 Op_subtract
        14        40 Semicolon
        15        16 Op_not
        15        40 Comma
        16        16 Op_multiply
        16        40 Op_assign
        17        16 Op_divide
        17        40 Integer 42
        18        16 Op_mod
        18        40 String "String literal"
        19        16 Op_add
        19        40 Identifier variable_name
        20        26 Integer 10
        21        26 Integer 92
        22        26 Integer 32
        23         1 End_of_Input

Nim

Tested with Nim v0.19.4. Both examples are tested against all programs in Compiler/Sample programs.

Using string with regular expressions

<lang nim> import re, strformat, strutils

type

 TokenKind = enum
   tkUnknown = "UNKNOWN_TOKEN",
   tkMul = "Op_multiply",
   tkDiv = "Op_divide",
   tkMod = "Op_mod",
   tkAdd = "Op_add",
   tkSub = "Op_subtract",
   tkNeg = "Op_negate",
   tkLt = "Op_less",
   tkLte = "Op_lessequal",
   tkGt = "Op_greater",
   tkGte = "Op_greaterequal",
   tkEq = "Op_equal",
   tkNeq = "Op_notequal",
   tkNot = "Op_not",
   tkAsgn = "Op_assign",
   tkAnd = "Op_and",
   tkOr = "Op_or",
   tkLpar = "LeftParen",
   tkRpar = "RightParen",
   tkLbra = "LeftBrace",
   tkRbra = "RightBrace",
   tkSmc = "Semicolon",
   tkCom = "Comma",
   tkIf = "Keyword_if",
   tkElse = "Keyword_else",
   tkWhile = "Keyword_while",
   tkPrint = "Keyword_print",
   tkPutc = "Keyword_putc",
   tkId = "Identifier",
   tkInt = "Integer",
   tkChar = "Integer",
   tkStr = "String",
   tkEof = "End_of_input"
 Token = object
   kind: TokenKind
   value: string
 TokenAnn = object
   ## Annotated token with messages for compiler
   token: Token
   line, column: int

proc getSymbols(table: openArray[(char, TokenKind)]): seq[char] =

 result = newSeq[char]()
 for ch, tokenKind in items(table):
   result.add ch

const

 tkSymbols = { # single-char tokens
   '*': tkMul,
   '%': tkMod,
   '+': tkAdd,
   '-': tkSub,
   '(': tkLpar,
   ')': tkRpar,
   '{': tkLbra,
   '}': tkRbra,
   ';': tkSmc,
   ',': tkCom,
   '/': tkDiv, # the comment case /* ... */ is handled in `stripUnimportant`
 }
 symbols = getSymbols(tkSymbols)

proc findTokenKind(table: openArray[(char, TokenKind)]; needle: char):

                 TokenKind =
 for ch, tokenKind in items(table):
   if ch == needle: return tokenKind
 tkUnknown

proc stripComment(text: var string, lineNo, colNo: var int) =

 var matches: array[1, string]
 if match(text, re"\A(/\*[\s\S]*?\*/)", matches):
   text = text[matches[0].len..^1]
   for s in matches[0]:
     if s == '\n':
       inc lineNo
       colNo = 1
     else:
       inc colNo

proc stripUnimportant(text: var string; lineNo, colNo: var int) =

 while true:
   if text.len == 0: return
   elif text[0] == '\n':
     inc lineNo
     colNo = 1
     text = text[1..^1]
   elif text[0] == ' ':
     inc colNo
     text = text[1..^1]
   elif text.len >= 2 and text[0] == '/' and text[1] == '*':
     stripComment(text, lineNo, colNo)
   else: return

proc lookAhead(ch1, ch2: char, tk1, tk2: TokenKind): (TokenKind, int) =

 if ch1 == ch2: (tk1, 2)
 else: (tk2, 1)

proc consumeToken(text: var string; tkl: var int): Token =

 ## Return token removing it from the `text` and write its length to
 ## `tkl`.  If the token can not be defined, return `tkUnknown` as a
 ## token, shrink text by 1 and write 1 to its length.
 var
   matches: array[1, string]
   tKind: TokenKind
   val: string
 if text.len == 0:
   (tKind, tkl) = (tkEof, 0)
 # Simple characters
 elif text[0] in symbols: (tKind, tkl) = (tkSymbols.findTokenKind(text[0]), 1)
 elif text[0] == '<': (tKind, tkl) = lookAhead(text[1], '=', tkLte, tkLt)
 elif text[0] == '>': (tKind, tkl) = lookAhead(text[1], '=', tkGte, tkGt)
 elif text[0] == '=': (tKind, tkl) = lookAhead(text[1], '=', tkEq, tkAsgn)
 elif text[0] == '!': (tKind, tkl) = lookAhead(text[1], '=', tkNeq, tkNot)
 elif text[0] == '&': (tKind, tkl) = lookAhead(text[1], '&', tkAnd, tkUnknown)
 elif text[0] == '|': (tKind, tkl) = lookAhead(text[1], '|', tkOr, tkUnknown)
 # Keywords
 elif match(text, re"\Aif\b"): (tKind, tkl) = (tkIf, 2)
 elif match(text, re"\Aelse\b"): (tKind, tkl) = (tkElse, 4)
 elif match(text, re"\Awhile\b"): (tKind, tkl) = (tkWhile, 5)
 elif match(text, re"\Aprint\b"): (tKind, tkl) = (tkPrint, 5)
 elif match(text, re"\Aputc\b"): (tKind, tkl) = (tkPutc, 4)
 # Literals and identifiers
 elif match(text, re"\A([0-9]+)", matches):
   (tKind, tkl) = (tkInt, matches[0].len)
   val = matches[0]
 elif match(text, re"\A([_a-zA-Z][_a-zA-Z0-9]*)", matches):
   (tKind, tkl) = (tkId, matches[0].len)
   val = matches[0]
 elif match(text, re"\A('(?:[^'\n]|\\\\|\\n)')", matches):
   (tKind, tkl) = (tkChar, matches[0].len)
   val = case matches[0]
         of r"' '": $ord(' ')
         of r"'\n'": $ord('\n')
         of r"'\\'": $ord('\\')
         else: $ord(matches[0][1]) # "'a'"[1] == 'a'
 elif match(text, re"\A(""[^""\n]*"")", matches):
   (tKind, tkl) = (tkStr, matches[0].len)
   val = matches[0]
 else: (tKind, tkl) = (tkUnknown, 1)
 text = text[tkl..^1]
 Token(kind: tKind, value: val)

proc tokenize*(text: string): seq[TokenAnn] =

 result = newSeq[TokenAnn]()
 var
   lineNo, colNo: int = 1
   text = text
   token: Token
   tokenLength: int
 while text.len > 0:
   stripUnimportant(text, lineNo, colNo)
   token = consumeToken(text, tokenLength)
   result.add TokenAnn(token: token, line: lineNo, column: colNo)
   inc colNo, tokenLength

proc output*(s: seq[TokenAnn]): string =

 var
   tokenKind: TokenKind
   value: string
   line, column: int
 for tokenAnn in items(s):
   line = tokenAnn.line
   column = tokenAnn.column
   tokenKind = tokenAnn.token.kind
   value = tokenAnn.token.value
   result.add(
     fmt"{line:>5}{column:>7} {tokenKind:<15}{value}"
       .strip(leading = false) & "\n")

when isMainModule:

 import os
 let input = if paramCount() > 0: readFile paramStr(1)
             else: readAll stdin
 echo input.tokenize.output

</lang>

Using stream with lexer library

<lang nim> import lexbase, streams from strutils import Whitespace

type

 TokenKind = enum
   tkInvalid = "Invalid",
   tkOpMultiply = "Op_multiply",
   tkOpDivide = "Op_divide",
   tkOpMod = "Op_mod",
   tkOpAdd = "Op_add",
   tkOpSubtract = "Op_subtract",
   tkOpLess = "Op_less",
   tkOpLessEqual = "Op_lessequal",
   tkOpGreater = "Op_greater",
   tkOpGreaterEqual = "Op_greaterequal",
   tkOpEqual = "Op_equal",
   tkOpNotEqual = "Op_notequal",
   tkOpNot = "Op_not",
   tkOpAssign = "Op_assign",
   tkOpAnd = "Op_and",
   tkOpOr = "Op_or",
   tkLeftParen = "LeftParen",
   tkRightParen = "RightParen",
   tkLeftBrace = "LeftBrace",
   tkRightBrace = "RightBrace",
   tkSemicolon = "Semicolon",
   tkComma = "Comma",
   tkKeywordIf = "Keyword_if",
   tkKeywordElse = "Keyword_else",
   tkKeywordWhile = "Keyword_while",
   tkKeywordPrint = "Keyword_print",
   tkKeywordPutc = "Keyword_putc",
   tkIdentifier = "Identifier",
   tkInteger = "Integer",
   tkString = "String",
   tkEndOfInput = "End_of_input"
 Lexer = object of BaseLexer
   kind: TokenKind
   token, error: string
   startPos: int

template setError(l: var Lexer; err: string): untyped =

 l.kind = tkInvalid
 if l.error.len == 0:
   l.error = err

proc hasError(l: Lexer): bool {.inline.} =

 l.error.len > 0

proc open(l: var Lexer; input: Stream) {.inline.} =

 lexbase.open(l, input)
 l.startPos = 0
 l.kind = tkInvalid
 l.token = ""
 l.error = ""

proc handleNewLine(l: var Lexer) =

 case l.buf[l.bufpos]
 of '\c': l.bufpos = l.handleCR l.bufpos
 of '\n': l.bufpos = l.handleLF l.bufpos
 else: discard

proc skip(l: var Lexer) =

 while true:
   case l.buf[l.bufpos]
   of Whitespace:
     if l.buf[l.bufpos] notin NewLines:
       inc l.bufpos
     else:
       handleNewLine l
   of '/':
     if l.buf[l.bufpos + 1] == '*':
       inc l.bufpos, 2
       while true:
         case l.buf[l.bufpos]
         of '*':
           if l.buf[l.bufpos + 1] == '/':
             inc l.bufpos, 2
             break
           else: inc l.bufpos
         of NewLines:
           handleNewLine l
         of EndOfFile:
           setError l, "EOF reached in comment"
           return
         else:
           inc l.bufpos
     else: break
   else: break

proc handleSpecial(l: var Lexer): char =

 assert l.buf[l.bufpos] == '\\'
 inc l.bufpos
 case l.buf[l.bufpos]
 of 'n':
   l.token.add "\\n"
   result = '\n'
   inc l.bufpos
 of '\\':
   l.token.add "\\\\"
   result = '\\'
   inc l.bufpos
 else:
   setError l, "Unknown escape sequence: '\\" & l.buf[l.bufpos] & "'"
   result = '\0'

proc handleChar(l: var Lexer) =

 assert l.buf[l.bufpos] == '\
 l.startPos = l.getColNumber l.bufpos
 l.kind = tkInvalid
 inc l.bufpos
 if l.buf[l.bufpos] == '\\':
   l.token = $ord(handleSpecial l)
   if hasError l: return
 elif l.buf[l.bufpos] == '\:
   setError l, "Empty character constant"
   return
 else:
   l.token = $ord(l.buf[l.bufpos])
   inc l.bufpos
 if l.buf[l.bufpos] == '\:
   l.kind = tkInteger
   inc l.bufpos
 else:
   setError l, "Multi-character constant"

proc handleString(l: var Lexer) =

 assert l.buf[l.bufpos] == '"'
 l.startPos = l.getColNumber l.bufpos
 l.token = "\""
 inc l.bufpos
 while true:
   case l.buf[l.bufpos]
   of '\\':
     discard handleSpecial l
     if hasError l: return
   of '"':
     l.kind = tkString
     add l.token, '"'
     inc l.bufpos
     break
   of NewLines:
     setError l, "EOL reached before end-of-string"
     return
   of EndOfFile:
     setError l, "EOF reached before end-of-string"
     return
   else:
     add l.token, l.buf[l.bufpos]
     inc l.bufpos

proc handleNumber(l: var Lexer) =

 assert l.buf[l.bufpos] in {'0'..'9'}
 l.startPos = l.getColNumber l.bufpos
 l.token = "0"
 while l.buf[l.bufpos] == '0': inc l.bufpos
 while true:
   case l.buf[l.bufpos]
   of '0'..'9':
     if l.token == "0":
       setLen l.token, 0
     add l.token, l.buf[l.bufpos]
     inc l.bufpos
   of 'a'..'z', 'A'..'Z', '_':
     setError l, "Invalid number"
     return
   else:
     l.kind = tkInteger
     break

proc handleIdent(l: var Lexer) =

 assert l.buf[l.bufpos] in {'a'..'z'}
 l.startPos = l.getColNumber l.bufpos
 setLen l.token, 0
 while true:
   if l.buf[l.bufpos] in {'a'..'z', 'A'..'Z', '0'..'9', '_'}:
     add l.token, l.buf[l.bufpos]
     inc l.bufpos
   else:
     break
 l.kind = case l.token
          of "if": tkKeywordIf
          of "else": tkKeywordElse
          of "while": tkKeywordWhile
          of "print": tkKeywordPrint
          of "putc": tkKeywordPutc
          else: tkIdentifier

proc getToken(l: var Lexer): TokenKind =

 l.kind = tkInvalid
 setLen l.token, 0
 skip l
 case l.buf[l.bufpos]
 of '*':
   l.kind = tkOpMultiply
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '/':
   l.kind = tkOpDivide
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '%':
   l.kind = tkOpMod
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '+':
   l.kind = tkOpAdd
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '-':
   l.kind = tkOpSubtract
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '<':
   l.kind = tkOpLess
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
   if l.buf[l.bufpos] == '=':
     l.kind = tkOpLessEqual
     inc l.bufpos
 of '>':
   l.kind = tkOpGreater
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
   if l.buf[l.bufpos] == '=':
     l.kind = tkOpGreaterEqual
     inc l.bufpos
 of '=':
   l.kind = tkOpAssign
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
   if l.buf[l.bufpos] == '=':
     l.kind = tkOpEqual
     inc l.bufpos
 of '!':
   l.kind = tkOpNot
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
   if l.buf[l.bufpos] == '=':
     l.kind = tkOpNotEqual
     inc l.bufpos
 of '&':
   if l.buf[l.bufpos + 1] == '&':
     l.kind = tkOpAnd
     l.startPos = l.getColNumber l.bufpos
     inc l.bufpos, 2
   else:
     setError l, "Unrecognized character"
 of '|':
   if l.buf[l.bufpos + 1] == '|':
     l.kind = tkOpOr
     l.startPos = l.getColNumber l.bufpos
     inc l.bufpos, 2
   else:
     setError l, "Unrecognized character"
 of '(':
   l.kind = tkLeftParen
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of ')':
   l.kind = tkRightParen
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '{':
   l.kind = tkLeftBrace
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '}':
   l.kind = tkRightBrace
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of ';':
   l.kind = tkSemicolon
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of ',':
   l.kind = tkComma
   l.startPos = l.getColNumber l.bufpos
   inc l.bufpos
 of '\: handleChar l
 of '"': handleString l
 of '0'..'9': handleNumber l
 of 'a'..'z', 'A'..'Z': handleIdent l
 of EndOfFile:
   l.startPos = l.getColNumber l.bufpos
   l.kind = tkEndOfInput
 else:
   setError l, "Unrecognized character"
 result = l.kind

when isMainModule:

 import os, strformat
 proc main() =
   var l: Lexer
   if paramCount() < 1:
     open l, newFileStream stdin
   else:
     open l, newFileStream paramStr(1)
   while l.getToken notin {tkInvalid}:
     stdout.write &"{l.lineNumber:5}  {l.startPos + 1:5} {l.kind:<14}"
     if l.kind in {tkIdentifier, tkInteger, tkString}:
       stdout.write &"  {l.token}"
     stdout.write '\n'
     if l.kind == tkEndOfInput:
       break
   if hasError l:
     echo &"({l.lineNumber},{l.getColNumber l.bufpos + 1}) {l.error}"

main() </lang>

Perl

<lang perl>#!/usr/bin/env perl

use strict; use warnings; no warnings 'once';


  1. ----- Definition of the language to be lexed -----#

my @tokens = (

   # Name            | Format               | Value       #
   # --------------  |----------------------|-------------#
   ['Op_multiply'    , '*'                  ,             ],
   ['Op_divide'      , '/'                  ,             ],
   ['Op_mod'         , '%'                  ,             ],
   ['Op_add'         , '+'                  ,             ],
   ['Op_subtract'    , '-'                  ,             ],
   ['Op_lessequal'   , '<='                 ,             ],
   ['Op_less'        , '<'                  ,             ],
   ['Op_greaterequal', '>='                 ,             ],
   ['Op_greater'     , '>'                  ,             ],
   ['Op_equal'       , '=='                 ,             ],
   ['Op_assign'      , '='                  ,             ],
   ['Op_not'         , '!'                  ,             ],
   ['Op_notequal'    , '!='                 ,             ],
   ['Op_and'         , '&&'                 ,             ],
   ['Op_or'          , '||'                 ,             ],
   ['Keyword_else'   , qr/else\b/           ,             ],
   ['Keyword_if'     , qr/if\b/             ,             ],
   ['Keyword_while'  , qr/while\b/          ,             ],
   ['Keyword_print'  , qr/print\b/          ,             ],
   ['Keyword_putc'   , qr/putc\b/           ,             ],
   ['LeftParen'      , '('                  ,             ],
   ['RightParen'     , ')'                  ,             ],
   ['LeftBrace'      , '{'                  ,             ],
   ['RightBrace'     , '}'                  ,             ],
   ['Semicolon'      , ';'                  ,             ],
   ['Comma'          , ','                  ,             ],
   ['Identifier'     , qr/[_a-z][_a-z0-9]*/i, \&raw       ],
   ['Integer'        , qr/[0-9]+\b/         , \&raw       ],
   ['Integer'        , qr/'([^']*)(')?/     , \&char_val  ],
   ['String'         , qr/"([^"]*)(")?/     , \&string_raw],
   ['End_of_input'   , qr/$/                ,             ],

);

my $comment = qr/\/\* .+? (?: \*\/ | $ (?{die "End-of-file in comment\n"}) )/xs; my $whitespace = qr/(?: \s | $comment)*/x; my $unrecognized = qr/\w+ | ./x;

  1. | Returns the value of a matched char literal, or dies if it is invalid

sub char_val {

   my $str = string_val();
   die "Multiple characters\n" if length $str > 1;
   die "No character\n"        if length $str == 0;
   ord $str;

}

  1. | Returns the value of a matched string literal, or dies if it is invalid

sub string_val {

   my ($str, $end) = ($1, $2);
   die "End-of-file\n" if not defined $end;
   die "End-of-line\n" if $str =~ /\n/;
   $str =~ s/\\(.)/
         $1 eq 'n'  ? "\n"
       : $1 eq '\\' ? $1
       : $1 eq $end ? $1
       : die "Unknown escape sequence \\$1\n"
   /rge;

}

  1. | Returns the source string of a matched literal

sub raw { $& }

  1. | Returns the source string of a matched string literal, or dies if invalid

sub string_raw {

   string_val(); # Just for the error handling side-effects
   $&;

}


  1. ----- Lexer "engine" -----#
  1. Construct the scanner regex:

my $tokens =

   join "|",
   map {
       my $format = $tokens[$_][1];
       "\n".(ref $format ? $format : quotemeta $format)." (*MARK:$_) ";
   } 0..$#tokens;

my $regex = qr/

   \G (?| $whitespace  \K (?| $tokens )
        | $whitespace? \K ($unrecognized) (*MARK:!) )

/x;


  1. Run the lexer:

my $input = do { local $/ = undef; <STDIN> }; my $pos = 0; my $linecol = linecol_accumulator();

while ($input =~ /$regex/g) {

   # Get the line and column number
   my ($line, $col) = $linecol->(substr $input, $pos, $-[0] - $pos);
   $pos = $-[0];
   # Get the token type that was identified by the scanner regex
   my $type = $main::REGMARK;
   die "Unrecognized token $1 at line $line, col $col\n" if $type eq '!';
   my ($name, $evaluator) = @{$tokens[$type]}[0, 2];
   # Get the token value
   my $value;
   if ($evaluator) {
       eval { $value = $evaluator->() };
       if ($@) { chomp $@; die "$@ in $name at line $line, col $col\n" }
   }
   # Print the output line
   print "$line\t$col\t$name".($value ? "\t$value" : )."\n";

}

  1. | Returns a closure, which can be fed a string one piece at a time and gives
  2. | back the cumulative line and column number each time

sub linecol_accumulator {

   my ($line, $col) = (1, 1);
   sub {
       my $str = shift;
       my @lines = split "\n", $str, -1;
       my ($l, $c) = @lines ? (@lines - 1, length $lines[-1]) : (0, 0);
       if ($l) { $line += $l;  $col = 1 + $c }
       else    { $col += $c }
       ($line, $col)
   }

}</lang>

Output  —  test case 3:
5       16      Keyword_print
5       40      Op_subtract
6       16      Keyword_putc
6       40      Op_less
7       16      Keyword_if
7       40      Op_greater
8       16      Keyword_else
8       40      Op_lessequal
9       16      Keyword_while
9       40      Op_greaterequal
10      16      LeftBrace
10      40      Op_equal
11      16      RightBrace
11      40      Op_not
11      41      Op_assign
12      16      LeftParen
12      40      Op_and
13      16      RightParen
13      40      Op_or
14      16      Op_subtract
14      40      Semicolon
15      16      Op_not
15      40      Comma
16      16      Op_multiply
16      40      Op_assign
17      16      Op_divide
17      40      Integer 42
18      16      Op_mod
18      40      String  "String literal"
19      16      Op_add
19      40      Identifier      variable_name
20      26      Integer 10
21      26      Integer 92
22      26      Integer 32
23      1       End_of_input

Alternate Perl Solution

Tested on perl v5.26.1 <lang Perl>#!/usr/bin/perl

use strict; # lex.pl - source to tokens use warnings; # http://www.rosettacode.org/wiki/Compiler/lexical_analyzer no warnings qw(qw);

my %keywords = map { $_, "Keyword_$_" } qw( while print if else putc ); my %tokens = qw[ ; Semicolon ( LeftParen ) RightParen { LeftBrace } RightBrace

 + Op_add - Op_subtract * Op_multiply % Op_mod = Op_assign >= Op_greaterequal
 != Op_notequal == Op_equal ! Op_not < Op_less <= Op_lessequal > Op_greater
 , Comma && Op_and || Op_or ];

local $_ = join , <>;

while( /\G (?|

   \s+              (?{ undef })
 | \d+[_a-zA-Z]\w*  (?{ die "invalid mixed number $&\n" })
 | \d+              (?{ "Integer $&" })
 | \w+              (?{ $keywords{$&} || "Identifier $&" })
 | ( [-;(){}+*%,] | [=!<>]=? | && | \|\| )
                    (?{ $tokens{$1} })
 | \/               (?{ 'Op_divide' }) (?: \* (?: [\s\S]*?\*\/ (?{ undef }) |
                         (?{ die "End-of-file in comment\n" }) ) )?
 | "[^"\n]*"        (?{ "String $&" })
 | "                (?{ die "unterminated string\n" })
 |                (?{ die "empty character constant\n" })
 | '([^\n\\])'      (?{ 'Integer ' . ord $1 })
 | '\\n'            (?{ 'Integer 10' })
 | '\\\\'           (?{ 'Integer 92' })
 | '                (?{ die "unterminated or bad character constant\n" }) #'
 | .                (?{ die "invalid character $&\n" })
 ) /gcx )
 {
 defined $^R and printf "%5d %7d   %s\n",
   1 + $` =~ tr/\n//, 1 + length $` =~ s/.*\n//sr, $^R;
 }

printf "%5d %7d %s\n", 1 + tr/\n//, 1, 'End_of_input';</lang>

Perl 6

This is more complicated than strictly necessary for this task. It is set up to be easily adapted to do syntax analysis.

(Note: there are several bogus comments added solely to help with syntax highlighting.)

Works with: Rakudo version 2016.08

<lang perl6>grammar tiny_C {

   rule TOP { ^ <.whitespace>? <tokens> + % <.whitespace> <.whitespace> <eoi> }
   rule whitespace { [ <comment> + % <ws> | <ws> ] }
   token comment    { '/*' ~ '*/' .*? }
   token tokens {
       [
       | <operator>   { make $/<operator>.ast   }
       | <keyword>    { make $/<keyword>.ast    }
       | <symbol>     { make $/<symbol>.ast     }
       | <identifier> { make $/<identifier>.ast }
       | <integer>    { make $/<integer>.ast    }
       | <char>       { make $/<char>.ast       }
       | <string>     { make $/<string>.ast     }
       | <error>
       ]
   }
   proto token operator    {*}
   token operator:sym<*>   { '*'               { make 'Op_multiply'    } }
   token operator:sym</>   { '/'<!before '*'>  { make 'Op_divide'      } }
   token operator:sym<%>   { '%'               { make 'Op_mod'         } }
   token operator:sym<+>   { '+'               { make 'Op_add'         } }
   token operator:sym<->   { '-'               { make 'Op_subtract'    } }
   token operator:sym('<='){ '<='              { make 'Op_lessequal'   } }
   token operator:sym('<') { '<'               { make 'Op_less'        } }
   token operator:sym('>='){ '>='              { make 'Op_greaterequal'} }
   token operator:sym('>') { '>'               { make 'Op_greater'     } }
   token operator:sym<==>  { '=='              { make 'Op_equal'       } }
   token operator:sym<!=>  { '!='              { make 'Op_notequal'    } }
   token operator:sym<!>   { '!'               { make 'Op_not'         } }
   token operator:sym<=>   { '='               { make 'Op_assign'      } }
   token operator:sym<&&>  { '&&'              { make 'Op_and'         } }
   token operator:sym<||>  { '||'              { make 'Op_or'          } }
   proto token keyword      {*}
   token keyword:sym<if>    { 'if'    { make 'Keyword_if'    } }
   token keyword:sym<else>  { 'else'  { make 'Keyword_else'  } }
   token keyword:sym<putc>  { 'putc'  { make 'Keyword_putc'  } }
   token keyword:sym<while> { 'while' { make 'Keyword_while' } }
   token keyword:sym<print> { 'print' { make 'Keyword_print' } }
   proto token symbol  {*}
   token symbol:sym<(> { '(' { make 'LeftParen'  } }
   token symbol:sym<)> { ')' { make 'RightParen' } }
   token symbol:sym<{> { '{' { make 'LeftBrace'  } }
   token symbol:sym<}> { '}' { make 'RightBrace' } }
   token symbol:sym<;> { ';' { make 'Semicolon'   } }
   token symbol:sym<,> { ',' { make 'Comma'       } }
   token identifier { <[_A..Za..z]><[_A..Za..z0..9]>* { make 'Identifier ' ~ $/ } }
   token integer    { <[0..9]>+                       { make 'Integer '    ~ $/ } }
   token char {
       '\ [<-[']> | '\n' | '\\\\'] '\
       { make 'Char_Literal ' ~ $/.subst("\\n", "\n").substr(1, *-1).ord }
   }
   token string {
       '"' <-["\n]>* '"' #'
       {
           make 'String ' ~ $/;
           note 'Error: Unknown escape sequence.' and exit if (~$/ ~~ m:r/ <!after <[\\]>>[\\<-[n\\]>]<!before <[\\]>> /);
       }
   }
   token eoi { $ { make 'End_of_input' } }
   token error {
       | '\'\                   { note 'Error: Empty character constant.' and exit }
       | '\ <-[']> ** {2..*} '\ { note 'Error: Multi-character constant.' and exit }
       | '/*' <-[*]>* $             { note 'Error: End-of-file in comment.'   and exit }
       | '"' <-["]>* $              { note 'Error: End-of-file in string.'    and exit }
       | '"' <-["]>*? \n            { note 'Error: End of line in string.'    and exit } #'
   }

}

sub parse_it ( $c_code ) {

   my $l;
   my @pos = gather for $c_code.lines>>.chars.kv -> $line, $v {
       take [ $line + 1, $_ ] for 1 .. ($v+1); # v+1 for newline
       $l = $line+2;
   }
   @pos.push: [ $l, 1 ]; # capture eoi
   for flat $c_code<tokens>.list, $c_code<eoi> -> $m {
       say join "\t", @pos[$m.from].fmt('%3d'), $m.ast;
   }

}

my $tokenizer = tiny_C.parse(@*ARGS[0].IO.slurp); parse_it( $tokenizer );</lang>

Output  —  test case 3:
  5  16 Keyword_print
  5  40 Op_subtract
  6  16 Keyword_putc
  6  40 Op_less
  7  16 Keyword_if
  7  40 Op_greater
  8  16 Keyword_else
  8  40 Op_lessequal
  9  16 Keyword_while
  9  40 Op_greaterequal
 10  16 LeftBrace
 10  40 Op_equal
 11  16 RightBrace
 11  40 Op_notequal
 12  16 LeftParen
 12  40 Op_and
 13  16 RightParen
 13  40 Op_or
 14  16 Op_subtract
 14  40 Semicolon
 15  16 Op_not
 15  40 Comma
 16  16 Op_multiply
 16  40 Op_assign
 17  16 Op_divide
 17  40 Integer 42
 18  16 Op_mod
 18  40 String "String literal"
 19  16 Op_add
 19  40	Identifier variable_name
 20  26	Char_Literal 10
 21  26	Char_Literal 92
 22  26	Char_Literal 32
 23   1	End_of_input

Phix

Deviates from the task requirements in that it is written in a modular form so that the output from one stage can be used directly in the next, rather than re-loading from a human-readable form. If required, demo\rosetta\Compiler\extra.e contains some code that achieves the latter. Code to print the human readable forms is likewise kept separate from any re-usable parts.

<lang Phix>-- -- demo\\rosetta\\Compiler\\core.e -- =============================== -- -- Standard declarations and routines used by lex.exw, parse.exw, cgen.exw, and interp.exw -- (included in distribution as above, which contains some additional sanity checks) -- -- global constant EOF = -1, STDIN = 0, STDOUT = 1

global enum type nary NONE=0, UNARY=1, BINARY=2 end type

global sequence tkNames = {} -- eg/ie {"Op_multiply","Op_divide",..} global sequence precedences = {} global sequence narys = {} -- NONE/UNARY/BINARY global sequence operators = {} -- eg/ie {"*","/","+","-","<","<=",..} global sequence opcodes = {} -- idx to tkNames, matching operators

global constant KEYWORDS = new_dict() -- eg/ie {"if"=>idx to tkNames}

global enum OPERATOR=1, DIGIT, LETTER -- character classes

global sequence charmap = repeat(0,255)

               charmap['0'..'9'] = DIGIT
               charmap['A'..'Z'] = LETTER
               charmap['a'..'z'] = LETTER
               charmap['_'] = LETTER

function tkName(string s, nary n = NONE, integer precedence = -1)

   tkNames = append(tkNames,s)
   narys = append(narys,n)
   precedences = append(precedences,precedence)
   return length(tkNames)

end function

function tkOp(string s, string op, nary n, integer precedence)

   integer res = tkName(s, n, precedence)
   operators = append(operators,op)
   opcodes = append(opcodes,res)
   for i=1 to length(op) do
       charmap[op[i]] = OPERATOR
   end for
   return res

end function

function tkKw(string s, string keyword)

   integer res = tkName(s)
   putd(keyword, res, KEYWORDS)
   return res

end function

global constant

   tk_EOI           = tkName("End_of_input"),                      --1
   tk_mul           = tkOp("Op_multiply",      "*", BINARY,13),    --2
   tk_div           = tkOp("Op_divide",        "/", BINARY,13),    --3
   tk_mod           = tkOp("Op_mod",           "%", BINARY,13),    --4
   tk_add           = tkOp("Op_add",           "+", BINARY,12),    --5
   tk_sub           = tkOp("Op_subtract",      "-", BINARY,12),    --6
   tk_neg           = tkName("Op_negate",           UNARY, 14),    --7
   tk_not           = tkOp("Op_not",           "!", UNARY, 14),    --8
   tk_lt            = tkOp("Op_less",          "<", BINARY,10),    --9
   tk_le            = tkOp("Op_lessequal",     "<=",BINARY,10),    --10
   tk_gt            = tkOp("Op_greater",       ">", BINARY,10),    --11
   tk_ge            = tkOp("Op_greaterequal",  ">=",BINARY,10),    --12
   tk_eq            = tkOp("Op_equal",         "==",BINARY, 9),    --13
   tk_ne            = tkOp("Op_notequal",      "!=",BINARY, 9),    --14
   tk_assign        = tkOp("Op_assign",        "=", NONE,  -1),    --15
   tk_and           = tkOp("Op_and",           "&&",BINARY, 5),    --16
   tk_or            = tkOp("Op_or",            "||",BINARY, 4),    --17
   tk_if            = tkKw("Keyword_if",   "if"),                  --18
   tk_else          = tkKw("Keyword_else", "else"),                --19
   tk_while         = tkKw("Keyword_while","while"),               --20
   tk_print         = tkKw("Keyword_print","print"),               --21
   tk_putc          = tkKw("Keyword_putc", "putc"),                --22
   tk_LeftParen     = tkOp("LeftParen",        "(", NONE,  -1),    --23
   tk_RightParen    = tkOp("RightParen",       ")", NONE,  -1),    --24
   tk_LeftBrace     = tkOp("LeftBrace",        "{", NONE,  -1),    --25
   tk_RightBrace    = tkOp("RightBrace",       "}", NONE,  -1),    --26
   tk_Semicolon     = tkOp("Semicolon",        ";", NONE,  -1),    --27
   tk_Comma         = tkOp("Comma",            ",", NONE,  -1),    --28
   tk_Identifier    = tkName("Identifier"),                        --29
   tk_Integer       = tkName("Integer"),                           --30
   tk_String        = tkName("String"),                            --31
   tk_Sequence      = tkName("Sequence"),                          --32
   tk_Prints        = tkName("tk_Prints"),                         --33
   tk_Printi        = tkName("tk_Printi")                          --34

global integer input_file = STDIN,

              output_file = STDOUT

type strint(object o)

   return string(o) or integer(o)

end type

global strint tok_line, -- save of line/col at the start of

             tok_col   -- token/comment, for result/errors

global object oneline = ""

constant errfmt = "Line %s column %s:\n%s%s"

function errline()

   oneline = substitute(trim(oneline,"\r\n"),"\t"," ")
   string padding = repeat(' ',tok_col)
   return sprintf("%s\n%s^ ",{oneline,padding})

end function

global procedure error(sequence msg, sequence args={})

   if length(args) then
       msg = sprintf(msg,args)
   end if
   string el = iff(atom(oneline)?"":errline())
   if integer(tok_line) then tok_line = sprintf("%d",tok_line) end if
   if integer(tok_col) then tok_col = sprintf("%d",tok_col) end if
   printf(STDOUT,errfmt,{tok_line,tok_col,el,msg})
   {} = wait_key()
   abort(1)

end procedure

function open_file(string file_name, string mode)

   integer fn = open(file_name, mode)
   if fn = -1 then
       printf(STDOUT, "Could not open %s", {file_name})
       {} = wait_key()
       abort(1)
   end if
   return fn

end function

global procedure open_files(sequence cl)

   if length(cl)>2 then
       input_file = open_file(cl[3],"r")
       if length(cl)>3 then
           output_file = open_file(cl[4],"w")
       end if
   end if

end procedure

global procedure close_files()

   if input_file!=STDIN then close(input_file) end if
   if output_file!=STDOUT then close(output_file) end if

end procedure

global function enquote(string s)

   return sprintf("\"%s\"",substitute(s,"\n","\\n"))

end function

global function unquote(string s)

   if s[1]!='\"' then ?9/0 end if
   if s[$]!='\"' then ?9/0 end if
   s = substitute(s[2..-2],"\\n","\n")
   return s

end function</lang> The main lexer is also written to be reusable by later stages. <lang Phix>-- -- demo\\rosetta\\Compiler\\lex.e -- ============================== -- -- The reusable part of lex.exw -- This is only kept separate from core.e for consistency with later modules.

include core.e

integer ch = ' ',

       line = 0,
       col = 0

procedure eof(string s)

   error("%s in %s literal",{iff(ch=EOF?"EOF":"EOL"),s})

end procedure

function next_ch()

   while 1 do
       col += 1
       if oneline=EOF then
           ch = EOF
           exit
       elsif col>length(oneline) then
           line += 1
           col = 0
           oneline = gets(input_file)
       else
           ch = oneline[col]
           exit
       end if
   end while
   return ch

end function

constant whitespace = " \t\r\n\x0B\xA0" -- (0x0B is Vertical Tab, 0xA0 is Non-breaking space)

procedure skipspacesandcomments()

   while 1 do
       if not find(ch,whitespace) then
           if ch='/' and col<length(oneline) and oneline[col+1]='*' then
               tok_line = line -- (in case of EOF error)
               tok_col = col
               ch = next_ch()  -- (can be EOF)
               ch = next_ch()  -- (    ""    )
               while 1 do
                   if ch='*' then
                       ch = next_ch()
                       if ch='/' then exit end if
                   elsif ch=EOF then
                       error("EOF in comment")
                   else
                       ch = next_ch()
                   end if
               end while
           else
               exit
           end if
       end if
       ch = next_ch()
   end while

end procedure

function escape_char(string s)

   ch = next_ch() -- (discard the '\\')
   if ch='n' then
       ch = '\n'
   elsif ch='\\' then
       ch = '\\'
   elsif ch=EOF
      or ch='\n' then
       eof(s)
   else
       error("unknown escape sequence \\%c", {ch})
   end if
   return ch

end function

function char_lit() integer startch = ch integer res = next_ch() -- (skip opening quote, save res)

   if ch=startch then
       error("empty character constant")
   elsif ch='\\' then
       res = escape_char("character")
   end if
   ch = next_ch()
   if ch=EOF
   or ch='\n' then
       eof("character")
   elsif ch!=startch then
       error("multi-character constant")
   end if
   ch = next_ch()
   return {tk_Integer, res}

end function

function string_lit() integer startch = ch string text = ""

   while next_ch()!=startch do
       if ch=EOF
       or ch='\n' then
           eof("string")
       elsif ch='\\' then
           ch = escape_char("string")
       end if
       text &= ch
   end while
   ch = next_ch()
   return {tk_String, text}

end function

function op() sequence operator = {ch}

   ch = next_ch()
   while charmap[ch]=OPERATOR
     and find(operator&ch,operators) do
       -- (^ ie/eg merge ">=", but not ");")
       operator &= ch
       ch = next_ch()
   end while
   integer k = find(operator,operators)
   if k=0 then error("unknown operator") end if
   return {opcodes[k], 0} -- (0 unused)

end function

function int() integer i = 0

   while charmap[ch]=DIGIT do
       i = i*10 + (ch-'0')
       ch = next_ch()
   end while
   if charmap[ch]=LETTER then
       error("invalid number")
   end if
   return {tk_Integer, i}

end function

function ident() string text = ""

   while find(charmap[ch],{LETTER,DIGIT}) do
       text &= ch
       ch = next_ch()
   end while
   integer keyword = getd(text,KEYWORDS)
   if keyword!=NULL then
       return {keyword, 0} -- (0 unused)
   end if
   return {tk_Identifier, text}

end function

function get_tok()

   skipspacesandcomments()
   tok_line = line
   tok_col  = col
   switch ch do
       case EOF  then return {tk_EOI, 0} -- (0 unused)
       case '\ then return char_lit()
       case '"'  then return string_lit()
       else
           switch charmap[ch] do
               case OPERATOR then return op()
               case DIGIT then return int()
               case LETTER then return ident()
               else error("unrecognized character: (%d)", {ch})
           end switch
   end switch

end function

global function lex() sequence toks = {}

   integer tok = -1
   object v
   while tok!=tk_EOI do
       {tok,v} = get_tok()
       toks = append(toks,{tok_line,tok_col,tok,v})
   end while
   return toks

end function</lang> Finally, a simple test driver for the specific task: <lang Phix>-- -- demo\\rosetta\\Compiler\\lex.exw -- ================================ --

include lex.e

procedure main(sequence cl)

   open_files(cl)
   sequence toks = lex()
   integer tok
   object v
   for i=1 to length(toks) do
       {tok_line,tok_col,tok,v} = toks[i]
       switch tok do
           case tk_Identifier: v = sprintf(" %s",v)
           case tk_Integer:    v = sprintf(" %5d",v)
           case tk_String:     v = sprintf(" %s",enquote(v))
           else                v = ""
       end switch
       printf(output_file, "%5d  %5d %-10s%s\n", {tok_line,tok_col,tkNames[tok],v})
   end for
   close_files()

end procedure

--main(command_line()) main({0,0,"test4.c"})</lang>

Output:
    2      1 Keyword_print
    2      6 LeftParen
    2      7 Integer       42
    2      9 RightParen
    2     10 Semicolon
    3      1 Keyword_print
    3      6 LeftParen
    3      7 String     "\nHello World\nGood Bye\nok\n"
    3     38 RightParen
    3     39 Semicolon
    4      1 Keyword_print
    4      6 LeftParen
    4      7 String     "Print a slash n - \n.\n"
    4     33 RightParen
    4     34 Semicolon
    5      1 End_of_input

Python

Tested with Python 2.7 and 3.x <lang Python>from __future__ import print_function import sys

  1. following two must remain in the same order

tk_EOI, tk_Mul, tk_Div, tk_Mod, tk_Add, tk_Sub, tk_Negate, tk_Not, tk_Lss, tk_Leq, tk_Gtr, \ tk_Geq, tk_Eq, tk_Neq, tk_Assign, tk_And, tk_Or, tk_If, tk_Else, tk_While, tk_Print, \ tk_Putc, tk_Lparen, tk_Rparen, tk_Lbrace, tk_Rbrace, tk_Semi, tk_Comma, tk_Ident, \ tk_Integer, tk_String = range(31)

all_syms = ["End_of_input", "Op_multiply", "Op_divide", "Op_mod", "Op_add", "Op_subtract",

   "Op_negate", "Op_not", "Op_less", "Op_lessequal", "Op_greater", "Op_greaterequal",
   "Op_equal", "Op_notequal", "Op_assign", "Op_and", "Op_or", "Keyword_if",
   "Keyword_else", "Keyword_while", "Keyword_print", "Keyword_putc", "LeftParen",
   "RightParen", "LeftBrace", "RightBrace", "Semicolon", "Comma", "Identifier",
   "Integer", "String"]
  1. single character only symbols

symbols = { '{': tk_Lbrace, '}': tk_Rbrace, '(': tk_Lparen, ')': tk_Rparen, '+': tk_Add, '-': tk_Sub,

   '*': tk_Mul, '%': tk_Mod, ';': tk_Semi, ',': tk_Comma }

key_words = {'if': tk_If, 'else': tk_Else, 'print': tk_Print, 'putc': tk_Putc, 'while': tk_While}

the_ch = " " # dummy first char - but it must be a space the_col = 0 the_line = 1 input_file = None

        • show error and exit

def error(line, col, msg):

   print(line, col, msg)
   exit(1)
        • get the next character from the input

def next_ch():

   global the_ch, the_col, the_line
   the_ch = input_file.read(1)
   the_col += 1
   if the_ch == '\n':
       the_line += 1
       the_col = 0
   return the_ch
        • 'x' - character constants

def char_lit(err_line, err_col):

   n = ord(next_ch())              # skip opening quote
   if the_ch == '\:
       error(err_line, err_col, "empty character constant")
   elif the_ch == '\\':
       next_ch()
       if the_ch == 'n':
           n = 10
       elif the_ch == '\\':
           n = ord('\\')
       else:
           error(err_line, err_col, "unknown escape sequence \\%c" % (the_ch))
   if next_ch() != '\:
       error(err_line, err_col, "multi-character constant")
   next_ch()
   return tk_Integer, err_line, err_col, n
        • process divide or comments

def div_or_cmt(err_line, err_col):

   if next_ch() != '*':
       return tk_Div, err_line, err_col
   # comment found
   next_ch()
   while True:
       if the_ch == '*':
           if next_ch() == '/':
               next_ch()
               return gettok()
       elif len(the_ch) == 0:
           error(err_line, err_col, "EOF in comment")
       else:
           next_ch()
        • "string"

def string_lit(start, err_line, err_col):

   text = ""
   while next_ch() != start:
       if len(the_ch) == 0:
           error(err_line, err_col, "EOF while scanning string literal")
       if the_ch == '\n':
           error(err_line, err_col, "EOL while scanning string literal")
       text += the_ch
   next_ch()
   return tk_String, err_line, err_col, text
        • handle identifiers and integers

def ident_or_int(err_line, err_col):

   is_number = True
   text = ""
   while the_ch.isalnum() or the_ch == '_':
       text += the_ch
       if not the_ch.isdigit():
           is_number = False
       next_ch()
   if len(text) == 0:
       error(err_line, err_col, "ident_or_int: unrecognized character: (%d) '%c'" % (ord(the_ch), the_ch))
   if text[0].isdigit():
       if not is_number:
           error(err_line, err_col, "invalid number: %s" % (text))
       n = int(text)
       return tk_Integer, err_line, err_col, n
   if text in key_words:
       return key_words[text], err_line, err_col
   return tk_Ident, err_line, err_col, text
        • look ahead for '>=', etc.

def follow(expect, ifyes, ifno, err_line, err_col):

   if next_ch() == expect:
       next_ch()
       return ifyes, err_line, err_col
   if ifno == tk_EOI:
       error(err_line, err_col, "follow: unrecognized character: (%d) '%c'" % (ord(the_ch), the_ch))
   return ifno, err_line, err_col
        • return the next token type

def gettok():

   while the_ch.isspace():
       next_ch()
   err_line = the_line
   err_col  = the_col
   if len(the_ch) == 0:    return tk_EOI, err_line, err_col
   elif the_ch == '/':     return div_or_cmt(err_line, err_col)
   elif the_ch == '\:    return char_lit(err_line, err_col)
   elif the_ch == '<':     return follow('=', tk_Leq, tk_Lss,    err_line, err_col)
   elif the_ch == '>':     return follow('=', tk_Geq, tk_Gtr,    err_line, err_col)
   elif the_ch == '=':     return follow('=', tk_Eq,  tk_Assign, err_line, err_col)
   elif the_ch == '!':     return follow('=', tk_Neq, tk_Not,    err_line, err_col)
   elif the_ch == '&':     return follow('&', tk_And, tk_EOI,    err_line, err_col)
   elif the_ch == '|':     return follow('|', tk_Or,  tk_EOI,    err_line, err_col)
   elif the_ch == '"':     return string_lit(the_ch, err_line, err_col)
   elif the_ch in symbols:
       sym = symbols[the_ch]
       next_ch()
       return sym, err_line, err_col
   else: return ident_or_int(err_line, err_col)
        • main driver

input_file = sys.stdin if len(sys.argv) > 1:

   try:
       input_file = open(sys.argv[1], "r", 4096)
   except IOError as e:
       error(0, 0, "Can't open %s" % sys.argv[1])

while True:

   t = gettok()
   tok  = t[0]
   line = t[1]
   col  = t[2]
   print("%5d  %5d   %-14s" % (line, col, all_syms[tok]), end=)
   if tok == tk_Integer:  print("   %5d" % (t[3]))
   elif tok == tk_Ident:  print("  %s" %   (t[3]))
   elif tok == tk_String: print('  "%s"' % (t[3]))
   else:                  print("")
   if tok == tk_EOI:
       break</lang>
Output  —  test case 3:

    5     16   Keyword_print
    5     40   Op_subtract
    6     16   Keyword_putc
    6     40   Op_less
    7     16   Keyword_if
    7     40   Op_greater
    8     16   Keyword_else
    8     40   Op_lessequal
    9     16   Keyword_while
    9     40   Op_greaterequal
   10     16   LeftBrace
   10     40   Op_equal
   11     16   RightBrace
   11     40   Op_notequal
   12     16   LeftParen
   12     40   Op_and
   13     16   RightParen
   13     40   Op_or
   14     16   Op_subtract
   14     40   Semicolon
   15     16   Op_not
   15     40   Comma
   16     16   Op_multiply
   16     40   Op_assign
   17     16   Op_divide
   17     40   Integer             42
   18     16   Op_mod
   18     40   String          "String literal"
   19     16   Op_add
   19     40   Identifier      variable_name
   20     26   Integer             10
   21     26   Integer             92
   22     26   Integer             32
   23      1   End_of_input

Racket

<lang racket>

  1. lang racket

(require parser-tools/lex)

(define-lex-abbrevs

 [letter         (union (char-range #\a #\z) (char-range #\A #\Z))]
 [digit          (char-range #\0 #\9)]
 [underscore     #\_]
 [identifier     (concatenation (union letter underscore)
                                (repetition 0 +inf.0 (union letter digit underscore)))]
 [integer        (repetition 1 +inf.0 digit)]
 [char-content   (char-complement (char-set "'\n"))]
 [char-literal   (union (concatenation #\' char-content #\')
                        "'\\n'" "'\\\\'")]
 [string-content (union (char-complement (char-set "\"\n")))]
 [string-literal (union (concatenation #\" (repetition 0 +inf.0 string-content) #\")
                        "\"\\n\"" "\"\\\\\"")]
 [keyword        (union "if" "else" "while" "print" "putc")]
 [operator       (union "*" "/" "%" "+" "-" "-"
                        "<" "<=" ">" ">=" "==" "!="
                        "!" "=" "&&" "||")]
 [symbol         (union "(" ")" "{" "}" ";" ",")]
 [comment        (concatenation "/*" (complement (concatenation any-string "*/" any-string)) "*/")])

(define operators-ht

 (hash "*"  'Op_multiply "/"  'Op_divide    "%" 'Op_mod      "+"  'Op_add           "-"  'Op_subtract
       "<"  'Op_less     "<=" 'Op_lessequal ">" 'Op_greater  ">=" 'Op_greaterequal "==" 'Op_equal
       "!=" 'Op_notequal "!"  'Op_not       "=" 'Op_assign   "&&" 'Op_and          "||" 'Op_or))

(define symbols-ht

 (hash "(" 'LeftParen  ")" 'RightParen
       "{" 'LeftBrace  "}" 'RightBrace
       ";" 'Semicolon  "," 'Comma))

(define (lexeme->keyword l) (string->symbol (~a "Keyword_" l))) (define (lexeme->operator l) (hash-ref operators-ht l)) (define (lexeme->symbol l) (hash-ref symbols-ht l)) (define (lexeme->char l) (match l

                              ["'\\\\'" #\\]
                              ["'\\n'"  #\newline]
                              [_       (string-ref l 1)]))

(define (token name [value #f])

 (cons name (if value (list value) '())))

(define (lex ip)

 (port-count-lines! ip)
 (define my-lexer
   (lexer-src-pos
    [integer        (token 'Integer (string->number lexeme))]
    [char-literal   (token 'Integer (char->integer (lexeme->char lexeme)))]
    [string-literal (token 'String  lexeme)]
    [keyword        (token (lexeme->keyword  lexeme))]
    [operator       (token (lexeme->operator lexeme))]
    [symbol         (token (lexeme->symbol   lexeme))]
    [comment        #f]
    [whitespace     #f]
    [identifier     (token 'Identifier lexeme)]
    [(eof)          (token 'End_of_input)]))
 (define (next-token) (my-lexer ip))
 next-token)

(define (string->tokens s)

 (port->tokens (open-input-string s)))

(define (port->tokens ip)

 (define next-token (lex ip))
 (let loop ()
   (match (next-token)
     [(position-token t (position offset line col) _)
      (set! col (+ col 1)) ; output is 1-based
      (match t
        [#f                   (loop)] ; skip whitespace/comments
        [(list 'End_of_input) (list (list line col 'End_of_input))]
        [(list name value)    (cons (list line col name value) (loop))]
        [(list name)          (cons (list line col name)       (loop))]
        [_ (error)])])))

(define test1 #<<TEST /*

 Hello world
*/

print("Hello, World!\n");

TEST )

(define test2 #<<TEST /*

 Show Ident and Integers
*/

phoenix_number = 142857; print(phoenix_number, "\n");

TEST

 )

(define test3 #<<TEST /*

 All lexical tokens - not syntactically correct, but that will
 have to wait until syntax analysis
*/

/* Print */ print /* Sub */ - /* Putc */ putc /* Lss */ < /* If */ if /* Gtr */ > /* Else */ else /* Leq */ <= /* While */ while /* Geq */ >= /* Lbrace */ { /* Eq */ == /* Rbrace */ } /* Neq */  != /* Lparen */ ( /* And */ && /* Rparen */ ) /* Or */ || /* Uminus */ - /* Semi */  ; /* Not */  ! /* Comma */ , /* Mul */ * /* Assign */ = /* Div */ / /* Integer */ 42 /* Mod */  % /* String */ "String literal" /* Add */ + /* Ident */ variable_name /* character literal */ '\n' /* character literal */ '\\' /* character literal */ ' ' TEST

 )

(define test4 #<<TEST /*** test printing, embedded \n and comments with lots of '*' ***/ print(42); print("\nHello World\nGood Bye\nok\n"); print("Print a slash n - \\n.\n"); TEST

 )

(define test5 #<<TEST count = 1; while (count < 10) {

   print("count is: ", count, "\n");
   count = count + 1;

} TEST

 )

(define (display-tokens ts)

 (for ([t ts])
   (for ([x t])
     (display x) (display "\t\t"))
   (newline)))

"TEST 1" (display-tokens (string->tokens test1)) "TEST 2" (display-tokens (string->tokens test2)) "TEST 3" (display-tokens (string->tokens test3)) "TEST 4" (display-tokens (string->tokens test4)) "TEST 5" (display-tokens (string->tokens test5)) </lang>

Scheme

<lang scheme> (import (scheme base)

       (scheme char)
       (scheme file)
       (scheme process-context)
       (scheme write))

(define *symbols* (list (cons #\( 'LeftParen)

                       (cons #\) 'RightParen)
                       (cons #\{ 'LeftBrace)
                       (cons #\} 'RightBrace)
                       (cons #\; 'Semicolon)
                       (cons #\, 'Comma)
                       (cons #\* 'Op_multiply)
                       (cons #\/ 'Op_divide)
                       (cons #\% 'Op_mod)
                       (cons #\+ 'Op_add)
                       (cons #\- 'Op_subtract)))

(define *keywords* (list (cons 'if 'Keyword_if)

                        (cons 'else 'Keyword_else)
                        (cons 'while 'Keyword_while)
                        (cons 'print 'Keyword_print)
                        (cons 'putc 'Keyword_putc)))
return list of tokens from current port

(define (read-tokens)

 ; information on position in input
 (define line 1) 
 (define col 0)
 (define next-char #f) 
 ; get char, updating line/col posn
 (define (get-next-char) 
   (if (char? next-char) ; check for returned character
     (let ((c next-char))
       (set! next-char #f)
       c)
     (let ((c (read-char)))
       (cond ((and (not (eof-object? c))
                   (char=? c #\newline))
              (set! col 0)
              (set! line (+ 1 line))
              (get-next-char))
             (else
               (set! col (+ 1 col))
               c)))))
 (define (push-char c)
   (set! next-char c))
 ; step over any whitespace or comments
 (define (skip-whitespace+comment)
   (let loop ()
     (let ((c (get-next-char)))
       (cond ((eof-object? c)
              '())
             ((char-whitespace? c) ; ignore whitespace
              (loop))
             ((char=? c #\/) ; check for comments
              (if (char=? (peek-char) #\*) ; found start of comment
                (begin ; eat comment
                  (get-next-char)
                  (let m ((c (get-next-char)))
                    (cond ((eof-object? c)
                           (error "End of file in comment"))
                          ((and (char=? c #\*)
                                (char=? (peek-char) #\/))
                           (get-next-char)) ; eat / and end
                          (else
                            (m (get-next-char)))))
                  (loop)) ; continue looking for whitespace / more comments
                (push-char #\/))) ; not comment, so put / back and return
             (else ; return to stream, as not a comment or space char
               (push-char c))))))
 ; read next token from input
 (define (next-token)
   (define (read-string) ; returns string value along with " "  marks
     (let loop ((chars '(#\"))) ; " (needed to appease Rosetta code's highlighter)
       (cond ((eof-object? (peek-char))
              (error "End of file while scanning string literal."))
             ((char=? (peek-char) #\newline)
              (error "End of line while scanning string literal."))
             ((char=? (peek-char) #\") ; " 
              (get-next-char) ; consume the final quote
              (list->string (reverse (cons #\" chars)))) ; "  highlighter)
             (else 
               (loop (cons (get-next-char) chars))))))
   (define (read-identifier initial-c) ; returns identifier as a Scheme symbol
     (do ((chars (list initial-c) (cons c chars))
          (c (get-next-char) (get-next-char)))
       ((or (eof-object? c) ; finish when hit end of file
            (not (or (char-numeric? c) ; or a character not permitted in an identifier
                     (char-alphabetic? c)
                     (char=? c #\_))))
        (push-char c) ; return last character to stream
        (string->symbol (list->string (reverse chars))))))
   (define (read-number initial-c) ; returns integer read as a Scheme integer
     (let loop ((res (digit-value initial-c))
                (c (get-next-char)))
       (cond ((char-alphabetic? c)
              (error "Invalid number - ends in alphabetic chars"))
             ((char-numeric? c)
              (loop (+ (* res 10) (digit-value c))
                    (get-next-char)))
             (else
               (push-char c) ; return non-number to stream
               res))))
   ; select op symbol based on if there is a following = sign
   (define (check-eq-extend start-line start-col opeq op)
     (if (char=? (peek-char) #\=)
       (begin (get-next-char) ; consume it
              (list start-line start-col opeq))
       (list start-line start-col op)))
   ;
   (let* ((start-line line)   ; save start position of tokens
          (start-col col)
          (c (get-next-char)))
     (cond ((eof-object? c)
            (list start-line start-col 'End_of_input))
           ((char-alphabetic? c) ; read an identifier
            (let ((id (read-identifier c)))
              (if (assq id *keywords*) ; check if identifier is a keyword
                (list start-line start-col (cdr (assq id *keywords*)))
                (list start-line start-col 'Identifier id))))
           ((char-numeric? c) ; read a number
            (list start-line start-col 'Integer (read-number c)))
           (else
             (case c
               ((#\( #\) #\{ #\} #\; #\, #\* #\/ #\% #\+ #\-)
                (list start-line start-col (cdr (assq c *symbols*))))
               ((#\<)
                (check-eq-extend start-line start-col 'Op_lessequal 'Op_less))
               ((#\>)
                (check-eq-extend start-line start-col 'Op_greaterequal 'Op_greater))
               ((#\=)
                (check-eq-extend start-line start-col 'Op_equal 'Op_assign))
               ((#\!)
                (check-eq-extend start-line start-col 'Op_notequal 'Op_not))
               ((#\& #\|)
                (if (char=? (peek-char) c) ; looks for && or || 
                  (begin (get-next-char) ; consume second character if valid
                         (list start-line start-col 
                               (if (char=? c #\&) 'Op_and 'Op_or)))
                  (push-char c)))
               ((#\") ; " 
                (list start-line start-col 'String (read-string)))
               ((#\')
                (let* ((c1 (get-next-char))
                       (c2 (get-next-char)))
                  (cond ((or (eof-object? c1)
                             (eof-object? c2))
                         (error "Incomplete character constant"))
                        ((char=? c1 #\')
                         (error "Empty character constant"))
                        ((and (char=? c2 #\') ; case of single character
                              (not (char=? c1 #\\)))
                         (list start-line start-col 'Integer (char->integer c1)))
                        ((and (char=? c1 #\\) ; case of escaped character
                              (char=? (peek-char) #\'))
                         (get-next-char) ; consume the ending '
                         (cond ((char=? c2 #\n)
                                (list start-line start-col 'Integer 10))
                               ((char=? c2 #\\)
                                (list start-line start-col 'Integer (char->integer c2)))
                               (else
                                 (error "Unknown escape sequence"))))
                        (else
                          (error "Multi-character constant")))))
               (else
                 (error "Unrecognised character")))))))
 ;
 (let loop ((tokens '())) ; loop, ignoring space/comments, while reading tokens
   (skip-whitespace+comment)
   (let ((tok (next-token)))
     (if (eof-object? (peek-char)) ; check if at end of input
       (reverse (cons tok tokens))
       (loop (cons tok tokens))))))

(define (lexer filename)

 (with-input-from-file filename 
                       (lambda () (read-tokens))))
output tokens to stdout, tab separated
line number, column number, token type, optional value

(define (display-tokens tokens)

 (for-each 
   (lambda (token)
     (display (list-ref token 0))
     (display #\tab) (display (list-ref token 1))
     (display #\tab) (display (list-ref token 2))
     (when (= 4 (length token))
       (display #\tab) (display (list-ref token 3)))
     (newline))
   tokens))
read from filename passed on command line

(if (= 2 (length (command-line)))

 (display-tokens (lexer (cadr (command-line))))
 (display "Error: provide program filename\n"))

</lang>

Output:

Output shown for "hello.c" example. Tested against all programs in Compiler/Sample programs.

4	1	Keyword_print
4	6	LeftParen
4	7	String	"Hello, World!\n"
4	24	RightParen
4	25	Semicolon
5	1	End_of_input