Compiler/lexical analyzer

From Rosetta Code
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).
Task[edit]

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:

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

/*
Hello world
*/

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

/*
Show Ident and Integers
*/

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

/*
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 */ ' '
    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:

/*** 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");
    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[edit]

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.
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[edit]

Tested with gawk 4.1.1 and mawk 1.3.4.

 
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)
}
 
# 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)
}
}
 
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[edit]

Tested with gcc 4.81 and later, compiles warning free with -Wall -Wextra

#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <ctype.h>
#include <string.h>
#include <errno.h>
#include <stdbool.h>
#include <limits.h>
 
#define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))
 
#define da_dim(name, type) type *name = NULL; \
int _qy_ ## name ## _p = 0; \
int _qy_ ## name ## _max = 0

#define da_rewind(name) _qy_ ## name ## _p = 0
#define da_redim(name) do {if (_qy_ ## name ## _p >= _qy_ ## name ## _max) \
name = realloc(name, (_qy_ ## name ## _max += 32) * sizeof(name[0]));} while (0)

#define da_append(name, x) do {da_redim(name); name[_qy_ ## name ## _p++] = x;} while (0)
#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;
}
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#[edit]

Requires C#6.0 because of the use of null coalescing operators.

 
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());
}
}
}
}
 
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[edit]

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

        >>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.
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[edit]

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.

(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 [email protected][ ~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*))
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[edit]

Tested with Euphoria 4.05.

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())
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[edit]

Tested with Flex 2.5.4.

%{
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <limits.h>
 
#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;
}
 
#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;
}
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[edit]

Tested with Gforth 0.7.3.

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
Output:

Tested against all programs in Compiler/Sample programs.

FreeBASIC[edit]

Tested with FreeBASIC 1.05

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
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

Perl[edit]

#!/usr/bin/env perl
 
use strict;
use warnings;
no warnings 'once';
 
 
#----- 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;
 
#| 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;
}
 
#| 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;
}
 
#| Returns the source string of a matched literal
sub raw { $& }
 
#| 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
$&;
}
 
 
#----- Lexer "engine" -----#
 
# 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;
 
 
# 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 ([email protected]) { chomp [email protected]; die "[email protected] in $name at line $line, col $col\n" }
}
 
# Print the output line
print "$line\t$col\t$name".($value ? "\t$value" : '')."\n";
}
 
#| Returns a closure, which can be fed a string one piece at a time and gives
#| 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)
}
}
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

Perl 6[edit]

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
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 );
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[edit]

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.

--
-- 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

The main lexer is also written to be reusable by later stages.

--
-- 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

Finally, a simple test driver for the specific task:

--
-- 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"})
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[edit]

Tested with Python 2.7 and 3.x

from __future__ import print_function
import sys
 
# 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"]
 
# 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
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

Scheme[edit]

 
(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"))
 
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