Compiler/Verifying syntax: Difference between revisions
Added Algol W
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=={{header|ALGOL W}}==
Includes the test cases from the Go sample. Note, strings are limited to 256 characters in Algol W.
<lang algolw>begin
% verify expressions match expected syntax %
procedure stmt ( string(256) value text ) ; begin
% the parsing procedures return truee if the expression matches the %
% the required element; false otherwise - a parse tree is not built %
boolean haveInteger, haveIdentifier, haveEof, hadError;
integer currPos, maxPos, syPos;
string(1) currCh;
string(256) srcText;
string(256) sy;
boolean procedure expr ; expr_level_2;
boolean procedure expr_level_2 ; begin
boolean ok;
ok := expr_level_3;
while ok and have( "or" ) do ok := next and expr_level_3;
ok
end expr_level_2 ;
boolean procedure expr_level_3 ; begin
boolean ok;
ok := expr_level_4;
while have( "and" ) and ok do ok := next and expr_level_4;
ok
end expr_level_3 ;
boolean procedure expr_level_4 ; begin
boolean ok;
ok := true;
if have( "not" ) then ok := next;
if ok then ok := expr_level_5;
if ok and ( have( "=" ) or have( "<" ) ) then ok := next and expr_level_5;
ok
end expr_level_4 ;
boolean procedure expr_level_5 ; begin
boolean ok;
ok := expr_level_6;
while ok and ( have( "+" ) or have( "-" ) ) do ok := next and expr_level_6;
ok
end expr_level_5 ;
boolean procedure expr_level_6 ; begin
boolean ok;
ok := primary;
while ok and ( have( "*" ) or have( "/" ) ) do ok := next and primary;
ok
end expr_level_6 ;
boolean procedure primary ;
if haveIdentifier or haveInteger or have( "true" ) or have( "false" )then begin
void( next );
true
end
else if have( "(" ) then next and expr and mustBe( ")" )
else error( "Expecting identifier, integer or ""(""" ) ;
logical procedure addAndNextChar ; begin
if syPos = 255 then void( error( "Symbol too long" ) )
else if syPos < 255 then begin
sy( syPos // 1 ) := currCh;
syPos := syPos + 1
end if_syPos_eq_255__lt_255 ;
nextChar
end addAndNextChar ;
boolean procedure next ; begin
logical ok;
haveInteger := haveIdentifier := false;
ok := skipSpaces;
sy := "";
syPos := 0;
if not ok then sy := "<eof>"
else begin
if haveDigit then begin
haveInteger := true;
while addAndNextChar and haveDigit do begin end
end
else if haveLetter then begin
while addAndNextChar and haveLetter or haveDigit or currCh = "_" do begin end;
haveIdentifier := sy not = "and" and sy not = "or" and sy not = "not" and sy not = "true" and sy not = "false"
end
else void( addAndNextChar );
end if_not_ok__ ;
ok
end next ;
boolean procedure skipSpaces ; begin
boolean ok;
ok := not haveEof;
while ok and currCh = " " do ok := nextChar;
ok
end skipSpaces ;
boolean procedure haveLetter ; not haveEof and ( ( currCh >= "a" and currCh <= "z" )
or ( currCh >= "A" and currCh <= "Z" ) );
boolean procedure haveDigit ; not haveEof and ( currCh >= "0" and currCh <= "9" );
boolean procedure have ( string(12) value text ) ; text = sy;
boolean procedure mustBe ( string(12) value text ) ; begin
boolean ok, haveSy;
ok := have( text );
if ok then haveSy := next
else begin
string(256) msg;
msg := "Expected:";
msg( strlen( msg ) + 2 // 12 ) := text;
void( error( msg ) )
end if_ok;
ok
end mustBe ;
boolean procedure nextChar ; begin
haveEof := currPos > maxPos;
if not haveEof then begin
currCh := srcText( currPos // 1 );
currPos := currPos + 1
end if_not_haveEof ;
not haveEof
end nextChar ;
integer procedure strlen ( string(256) value text ) ; begin
integer length;
length := 255;
while length >= 0 and text( length // 1 ) = " " do length := length - 1;
length
end strlen ;
boolean procedure error ( string(256) value msg ) ; begin
if not hadError then begin
% have the first error %
writeon( " error at: ", I_W := 1, currPos, "(" );
showText( sy, strlen( sy ) );
writeon( "): " );
showText( msg, strlen( msg ) );
hadError := true
end if_not_hadError ;
false
end ewrror ;
procedure showText ( string(256) value text; integer value length ) ; for c := 0 until length do writeon( text( c // 1 ) );
procedure void ( boolean value b ) ; begin end void ;
% parse text and output messages indicating whether it is OK or not %
hadError := false;
sy := "<bof>";
srcText := text;
currPos := 0;
maxPos := strlen( srcText );
write();
showText( srcText, maxPos );
writeon( ": " );
if not nextChar then void( error( "Blank source text" ) )
else if not ( next and expr ) then void( error( "Expression expected" ) )
else if not haveEof then void( error( "Expected EOF after expression" ) );
if hadError then writeon( " false" )
else writeon( " true" )
end stmt ;
% test cases %
stmt( "wombat" );
stmt( "wombat or monotreme" );
stmt( "a + 1" );
stmt( "a + b < c" );
stmt( "a + b - c * d / e < f and not ( g = h )" );
stmt( "a + b - c * d / e < f and not ( g = h" );
stmt( "a = b" );
stmt( "a or b = c" );
stmt( "$" );
% test cases from Go %
stmt( "3 + not 5" );
stmt( "3 + (not 5)" );
stmt( "(42 + 3" );
stmt( " not 3 < 4 or (true or 3 / 4 + 8 * 5 - 5 * 2 < 56) and 4 * 3 < 12 or not true" );
stmt( " and 3 < 2" );
stmt( "not 7 < 2" );
stmt( "2 < 3 < 4" );
stmt( "2 < foobar - 3 < 4" );
stmt( "2 < foobar and 3 < 4" );
stmt( "4 * (32 - 16) + 9 = 73" );
stmt( "235 76 + 1" );
stmt( "a + b = not c and false" );
stmt( "a + b = (not c) and false" );
stmt( "a + b = (not c and false)" );
stmt( "ab_c / bd2 or < e_f7" );
stmt( "g not = h" );
stmt( "été = false" );
stmt( "i++" );
stmt( "j & k" );
stmt( "l or _m" )
end.</lang>
{{out}}
<pre>
wombat: true
wombat or monotreme: true
a + 1: true
a + b < c: true
a + b - c * d / e < f and not ( g = h ): true
a + b - c * d / e < f and not ( g = h: error at: 37 (<eof>): Expected: ) false
a = b: true
a or b = c: true
$: error at: 1 ($): Expecting identifier, integer or "(" false
3 + not 5: error at: 8 (not): Expecting identifier, integer or "(" false
3 + (not 5): true
(42 + 3: error at: 7 (<eof>): Expected: ) false
not 3 < 4 or (true or 3 / 4 + 8 * 5 - 5 * 2 < 56) and 4 * 3 < 12 or not true: true
and 3 < 2: error at: 5 (and): Expecting identifier, integer or "(" false
not 7 < 2: true
2 < 3 < 4: error at: 8 (<): Expected EOF after expression false
2 < foobar - 3 < 4: error at: 17 (<): Expected EOF after expression false
2 < foobar and 3 < 4: true
4 * (32 - 16) + 9 = 73: true
235 76 + 1: error at: 7 (76): Expected EOF after expression false
a + b = not c and false: error at: 12 (not): Expecting identifier, integer or "(" false
a + b = (not c) and false: true
a + b = (not c and false): true
ab_c / bd2 or < e_f7: error at: 16 (<): Expecting identifier, integer or "(" false
g not = h: error at: 6 (not): Expected EOF after expression false
été = false: error at: 2 (Ã): Expecting identifier, integer or "(" false
i++: error at: 3 (+): Expecting identifier, integer or "(" false
j & k: error at: 4 (&): Expected EOF after expression false
l or _m: error at: 7 (_): Expecting identifier, integer or "(" false
</pre>
=={{header|Go}}==
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