I created an ANTLR grammar for parsing mathematical expressions and a second one for evaluating them. As I thought building an AST and then re-parsing in order to actually evaluate it is sort of one operation too much, I wanted to refactor my grammar to produce a hierarchy of "Term" objects representing the expression including the logic to perform that particular operation. The root Term object can then be simply evaluated to a concrete result.
I had to rewrite quite a lot of my grammar and finally got rid of the last error message. Unfortunately now ANTLR seems to sort of go into an infinite loop.
Could someone here please help me sort out the problem? I think the grammar should be pretty interesting for some, therefore I am posting it. (It is based upon a garmmar I found with google, I should admit, but I have altered it quite a lot to suite my needs).
grammar SecurityRulesNew;
options {
language = Java;
output=AST;
backtrack = true;
ASTLabelType=CommonTree;
k=2;
}
tokens {
POS;
NEG;
CALL;
}
@header {package de.cware.cweb.services.evaluator.parser;}
@lexer::header{package de.cware.cweb.services.evaluator.parser;}
formula returns [Term term]
: a=expression EOF { $term = a; }
;
expression returns [Term term]
: a=boolExpr { $term = a; }
;
boolExpr returns [Term term]
: a=sumExpr { $term = a; }
| a=sumExpr AND b=boolExpr { $term = new AndTerm(a, b); }
| a=sumExpr OR b=boolExpr { $term = new OrTerm(a, b); }
| a=sumExpr LT b=boolExpr { $term = new LessThanTerm(a, b); }
| a=sumExpr LTEQ b=boolExpr { $term = new LessThanOrEqualTerm(a, b); }
| a=sumExpr GT b=boolExpr { $term = new GreaterThanTerm(a, b); }
| a=sumExpr GTEQ b=boolExpr { $term = new GreaterThanTermOrEqual(a, b); }
| a=sumExpr EQ b=boolExpr { $term = new EqualsTerm(a, b); }
| a=sumExpr NOTEQ b=boolExpr { $term = new NotEqualsTerm(a, b); }
;
sumExpr returns [Term term]
: a=productExpr { $term = a; }
| a=productExpr SUB b=sumExpr { $term = new SubTerm(a, b); }
| a=productExpr ADD b=sumExpr { $term = new AddTerm(a, b); }
;
productExpr returns [Term term]
: a=expExpr { $term = a; }
| a=expExpr DIV productExpr { $term = new DivTerm(a, b); }
| a=expExpr MULT productExpr { $term = new MultTerm(a, b); }
;
expExpr returns [Term term]
: a=unaryOperation { $term = a; }
| a=unaryOperation EXP expExpr { $term = new ExpTerm(a, b); }
;
unaryOperation returns [Term term]
: a=operand { $term = a; }
| NOT a=operand { $term = new NotTerm(a); }
| SUB a=operand { $term = new NegateTerm(a); }
;
operand returns [Term term]
: l=literal { $term = l; }
| f=functionExpr { $term = f; }
| v=VARIABLE { $term = new VariableTerm(v); }
| LPAREN e=expression RPAREN { $term = e; }
;
functionExpr returns [Term term]
: f=FUNCNAME LPAREN! RPAREN! { $term = new CallFunctionTerm(f, null); }
| f=FUNCNAME LPAREN! a=arguments RPAREN! { $term = new CallFunctionTerm(f, a); }
;
arguments returns [List<Term> terms]
: a=expression
{
$terms = new ArrayList<Term>();
$terms.add(a);
}
| a=expression COMMA b=arguments
{
$terms = new ArrayList<Term>();
$terms.add(a);
$terms.addAll(b);
}
;
literal returns [Term term]
: n=NUMBER { $term = new NumberLiteral(n); }
| s=STRING { $term = new StringLiteral(s); }
| t=TRUE { $term = new TrueLiteral(t); }
| f=FALSE { $term = new FalseLiteral(f); }
;
STRING
:
'\"'
( options {greedy=false;}
: ESCAPE_SEQUENCE
| ~'\\'
)*
'\"'
|
'\''
( options {greedy=false;}
: ESCAPE_SEQUENCE
| ~'\\'
)*
'\''
;
WHITESPACE
: (' ' | '\n' | '\t' | '\r')+ {skip();};
TRUE
: ('t'|'T')('r'|'R')('u'|'U')('e'|'E')
;
FALSE
: ('f'|'F')('a'|'A')('l'|'L')('s'|'S')('e'|'E')
;
NOTEQ : '!=';
LTEQ : '<=';
GTEQ : '>=';
AND : '&&';
OR : '||';
NOT : '!';
EQ : '=';
LT : '<';
GT : '>';
EXP : '^';
MULT : '*';
DIV : '/';
ADD : '+';
SUB : '-';
LPAREN : '(';
RPAREN : ')';
COMMA : ',';
PERCENT : '%';
VARIABLE
: '[' ~('[' | ']')+ ']'
;
FUNCNAME
: (LETTER)+
;
NUMBER
: (DIGIT)+ ('.' (DIGIT)+)?
;
fragment
LETTER
: ('a'..'z') | ('A'..'Z')
;
fragment
DIGIT
: ('0'..'9')
;
fragment
ESCAPE_SEQUENCE
: '\\' 't'
| '\\' 'n'
| '\\' '\"'
| '\\' '\''
| '\\' '\\'
;
Help is greatly appreciated.
Chris
