Greetings!
I think you have issues with your function, number, and ATOM rules. see
below...
I have attached my complete, modified, grammar that successfully parses
your input sample.
On 11/14/2011 11:47 PM, Jarrod Roberson wrote:
> I am trying to write a parser for the following syntax
>
> hypotenuse(a,b) ->
> sqr(x) -> x * x,
> sqr(sqr(b) + sqr(b)).
>
> print(hypotenuse(2,3)).
>
> Where , and . are my statement separator and statement eol respectively.
>
> I am having an impossible time trying to figure out how to specify the
> function rule to allow me to nest functions inside of other functions
> without running afoul of ambiguities warnings.
>
> 23:37:47] warning(200): funcy.g:10:11: Decision can match input such as
> "ID" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
> [23:37:47] error(201): funcy.g:10:11: The following alternatives can never
> be matched: 2
>
>
> I really want to be able to use the above syntax without having to pepper
> the code with keywords like `func` or `var` etc.
>
> Here is my grammar, are there any ways to resolve these ambiguities with
> predicates of some sort that I haven't been able to figure out?
>
> I have read up on Google about them, but I can't get them to work with the
> parser rules to remove the ambiguities.
>
> grammar funcy;
>
> options {
> output = AST;
> language = Java;
> }
> program : (statement'.')* ;
just a nit pick here - you really should include EOF in your topmost rule.
>
> statement : expression
> | assignment
> ;
>
> assignment : ID '->' expression
> | ATOM '->' ( string | number )
> | function '->' statement ((','statement)=> ',' statement)* ;
I think you are being too liberal here with your function signatures.
you permit any expression to be a formal argument. are you intending to
have patterns akin to either ML or Haskell? if not, change the
definition of function in your assignment rule.
I also think that this permits multi-expression body, something like:
foo(a,b)-> a, b.
e.g. a function body consisting of two (or more) expressions. do you
really want that -- you do if your expressions can have side-effects.
maybe the third alt of assignment rule should be something like
(assuming you do not have side effects and watch out for i/o!):
| ID '(' ID (',' ID)* ')' '->' (assignment ',')* expression ;
this eliminates the need for a predicate.
>
> args : expression (',' expression)*;
>
> function : ID '(' args ')' ;
>
> string : UNICODE_STRING;
> number : HEX_NUMBER
> | (INTEGER '.' INTEGER)=> INTEGER '.' INTEGER
I do not think you want to recognize floating point values in the
parser. any tokens you send to the HIDDEN $channel (or skip();) will be
silently accepted before and after the '.' of the float. change your
INTEGER rule to this:
fragment FLOAT: ;
INTEGER : DIGIT+ ('.' DIGIT+ {$type=FLOAT;} )? ;
and use FLOAT in the number rule.
> | INTEGER;
>
> // expressions
>
> term : '(' expression ')'
> | number
> | string
> | function
> | ID
> | ATOM
> ;
>
> negation : '!'* term;
>
> unary : ('+'|'-')* negation;
>
> mult : unary (('*' | '/' | ('%'|'mod') ) unary)*;
>
> add : mult (('+' | '-') mult)*;
>
> relation : add (('=' | '!=' | '<' | '<=' | '>=' | '>') add)*;
> expression : relation (('&&' | '||') relation)*;
>
> // LEXER ================================================================
>
> HEX_NUMBER : '0x' HEX_DIGIT+;
>
> INTEGER : DIGIT+;
>
> UNICODE_STRING : '"' ( ESC | ~('\u0000'..'\u001f' | '\\' | '\"' ) )* '"'
> ;
>
> WS : (' '|'\n'|'\r'|'\t')+ {$channel = HIDDEN;} ; // ignore whitespace
>
> fragment
> ESC : '\\' ( UNI_ESC |'b'|'t'|'n'|'f'|'r'|'\"'|'\''|'\\' );
>
> fragment
> UNI_ESC : 'u' HEX_DIGIT HEX_DIGIT HEX_DIGIT HEX_DIGIT;
>
> fragment
> HEX_DIGIT : (DIGIT|'a'..'f'|'A'..'F') ;
>
> fragment
> DIGIT : ('0'..'9');
>
> ATOM : (('A'..'Z'|'_')+)=> ('A'..'Z'|'0'..'9'|'_')+;
no need for a predicate
ATOM : ('A'..'Z')('A'..'Z'|'0'..'9'|'_')*;
note that this also removes the ambiguity as to whether the string "_"
is an ATOM or an ID.
>
> ID : ('a'..'z'|'_')('a'..'z'|'A'..'Z'|'0'..'9'|'_')*;
>
> COMMENT : '/*' .* '*/' {$channel = HIDDEN;};
>
grammar Test;
options {
output = AST;
ASTLabelType = CommonTree;
}
@members {
// test data - each string in the following array is parsed separately
private static final String [] x = new String[] {
"hypotenuse(a,b) ->\n" +
" sqr(x) -> x * x,\n" +
" sqr(sqr(b) + sqr(b)).\n" +
"\n" +
"print(hypotenuse(2,3)).\n",
};
public static void main(String [] args) {
for( int i = 0; i < x.length; ++i ) {
try {
System.out.println("about to parse:`"+x[i]+"`");
TestLexer lexer = new TestLexer(new ANTLRStringStream(x[i]));
CommonTokenStream tokens = new CommonTokenStream(lexer);
// System.out.format("dump of the token stream:\%n");
// int j = 0;
// boolean looping = true;
// while( looping ) {
// Token token = lexer.nextToken();
// int typ = token.getType();
// System.out.format("\%d: type = \%s, text = `\%s`\%s\%n",
// j++,
// typ==EOF?"EOF":tokenNames[typ],
// token.getText(),
// token.getChannel()==HIDDEN?" (HIDDEN)":"");
// looping = typ != EOF;
// }
// lexer.reset();
// System.out.format("now performing the parse\n");
TestParser parser = new TestParser(tokens);
TestParser.test_return p_result = parser.test();
CommonTree ast = p_result.tree;
if( ast == null ) {
System.out.println("resultant tree: is NULL");
} else {
System.out.println("resultant tree: " + ast.toStringTree());
}
System.out.println();
} catch(Exception e) {
e.printStackTrace();
}
}
}
}
test : program EOF! ;
program : (statement'.')* ;
statement : expression
| assignment
;
assignment : ID '->' expression
| ATOM '->' ( string | number )
| function_signature '->' ( assignment ',' )* expression ;
// | function_signature '->' statement ((','statement)=> ','
statement)* ;
function_signature : ID '(' ID (',' ID)* ')' ;
function_invocation : ID '(' expression (',' expression)* ')' ;
string : UNICODE_STRING;
number : HEX_NUMBER
| FLOAT
| INTEGER;
// expressions
term : '(' expression ')'
| number
| string
| function_invocation
| ID
| ATOM
;
negation : '!'* term;
unary : ('+'|'-')* negation;
mult : unary (('*' | '/' | ('%'|'mod') ) unary)*;
add : mult (('+' | '-') mult)*;
relation : add (('=' | '!=' | '<' | '<=' | '>=' | '>') add)*;
expression : relation (('&&' | '||') relation)*;
// LEXER ================================================================
HEX_NUMBER : '0x' HEX_DIGIT+;
fragment FLOAT : ;
INTEGER : DIGIT+ ('.' DIGIT+ { $type = FLOAT; })? ;
UNICODE_STRING : '"' ( ESC | ~('\u0000'..'\u001f' | '\\' | '\"' ) )* '"'
;
WS : (' '|'\n'|'\r'|'\t')+ {$channel = HIDDEN;} ; // ignore whitespace
fragment
ESC : '\\' ( UNI_ESC |'b'|'t'|'n'|'f'|'r'|'\"'|'\''|'\\' );
fragment
UNI_ESC : 'u' HEX_DIGIT HEX_DIGIT HEX_DIGIT HEX_DIGIT;
fragment
HEX_DIGIT : (DIGIT|'a'..'f'|'A'..'F') ;
fragment
DIGIT : ('0'..'9');
ATOM : ('A'..'Z')('A'..'Z'|'0'..'9'|'_')*;
ID : ('a'..'z'|'_')('a'..'z'|'A'..'Z'|'0'..'9'|'_')*;
COMMENT : '/*' .* '*/' {$channel = HIDDEN;};
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