I am a total ANTLR newbie, and have read quite a bit, but am a bit
flumoxed by the results I am getting with my antlr grammar
My grammar is heavily based on the expression parser example.
I am confused by some console output I am seeing of the form:
line 1:5 no viable alternative at input '&&'
line 0:-1 no viable alternative at input '<EOF>'
line 1:5 no viable alternative at input '&&'
line 0:-1 no viable alternative at input '<EOF>'
Despite seeing this console output, my boolean expression parser seems
to work & return valid values.
All the "operators" in my base parser get called with the values I
would expect
so when I give it the input
true && true
despite the fact that I get the following consle messages
line 1:5 no viable alternative at input '&&'
line 0:-1 no viable alternative at input '<EOF>'
My method band() gets called with 2 Boolean, both set to true
If I pass input
false || true
my method bor() gets called with the Boolean values false & true
I also intended it to support more complex expressions like
(1.1 < 2.2) && (((1/1.0) * (4.0-8)) > -5.0)
Once again we get console output about no viable alternative
but the final result of the expression is as expected.
I have attached the grammar below
I am using antlr 3.0.1 with Java 5 on a Mac 10.5
I would really appreciate any hints that you might be able to provide
Regards,
Matthew
=== GRAMMAR ====
grammar Expr;
options {
superClass=ExprParserBase;
}
@header {
package au.com.observant.viz.expression;
import au.com.observant.viz.expression.ExprParserBase;
}
@lexer::header {
package au.com.observant.viz.expression;
}
@members {
Object result;
public Object getResult() {
return result;
}
}
prog returns [Object value]
: b=boolExpr {$value = $b.value;}
;
boolExpr returns [Object value]
: b=relExpr {$value = $b.value;}
( BAND b=relExpr {$value = band($value,$b.value);}
| BOR b=relExpr {$value = bor($value,$b.value);}
)*
;
relExpr returns [Object value]
: e=expr {$value = $e.value;}
( '>' e=expr {$value = gt($value,$e.value);}
| '<' e=expr {$value = lt($value,$e.value);}
| '>=' e=expr {$value = gte($value,$e.value);}
| '<=' e=expr {$value = lte($value,$e.value);}
| '==' e=expr {$value = eq($value,$e.value);}
| '!=' e=expr {$value = neq($value,$e.value);}
)
;
expr returns [Object value]
: e=multExpr {$value = $e.value;}
( '+' e=multExpr {$value = add($value,$e.value);}
| '-' e=multExpr {$value = subtract($value,$e.value);}
)*
;
multExpr returns [Object value]
: e=power {$value = $e.value;}
( '*' e=power {$value = multiply($value, $e.value);}
| '/' e=power {$value = divide($value, $e.value);}
)*
;
power returns [Object value]
: f=unary
{$value = $f.value;}
(POW p=unary
{$value=powerOf($value,$p.value);}
)?
;
unary returns [Object value]
: f=atom
{$value = $f.value;}
| '!' f=atom
{$value = negate($f.value);}
| '-' f=atom
{$value = negate($f.value);}
;
atom returns [Object value]
: INTEGER {$value = Double.parseDouble($INTEGER.text);}
| FLOAT {$value = Double.parseDouble($FLOAT.text);}
| FIELD { $value = findField($FIELD.text); }
| ID { $value = findField($ID.text); }
| '(' boolExpr ')' {$value = $boolExpr.value;}
| EXP '(' expr ')' {$value = exp($expr.value);}
| TRUE {$value = Boolean.TRUE;}
| FALSE {$value = Boolean.FALSE;}
;
EXP : 'exp';
TRUE : 'true';
FALSE : 'false';
ID : LETTER ( LETTER | '0'..'9' | '_' )*;
fragment LETTER: ('a'..'z' | 'A'..'Z');
POW : '^';
BAND : '&&';
BOR : '||';
INTEGER
: ('0'..'9')+
;
FLOAT
: ('0'..'9')* '.' ('0'..'9')+
;
FIELD : ID '.' ID ;
WS : (' '|'\t')+ {skip();} ;
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