[antlr-interest] Rule parameter troubles

[Jim Idle]

When you use the predicate, it is being hoisted into other rules, where it is out of context. So, rather than pass as a parameter, use in a scope at a high enough rule level and then use the scope reference in your predicate.

 

Also, if you can, allow all syntax through in the parser even if it makes no semantic sense, and reject it with a better error message at a later semantic phase (usually a tree parser). Then you won't need the flags unless allowing such a syntactic construct means an ambiguous grammar of some kind. Basically you are trying to trade "Syntax error at 'wtf'" for "You cannot have more than one 'wtf' constructs with a 'foo'"

 

Jim

 

From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Andrew Bradnan
Sent: Saturday, November 28, 2009 11:14 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] Rule parameter troubles

 

I was trying to use a rule parameter and can't call another rule with that parameter when I use +.  An example will make more sense.

 

test [bool wtf] returns [int n]:
    {$wtf}?=>'wtf' test2[$wtf]+;    // attribute is not a token, parameter, or return value: wtf

test [bool wtf] returns [int n]:
    {$wtf}?=>'wtf' test2[$wtf];    // works fine

 

test [bool wtf] returns [int n]:
    {$wtf}?=>'wtf' test2[false]+;  // works fine as well

test2 [bool wtf2]:
    {$wtf2}?=>'foobar';

If I take the gated semantic predicate out of test2, then all the above work.
test2 [bool wtf2]:
    'foobar';    // works for all the above

What did I miss?

Thanks
-- 
/Andrew



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