[antlr-interest] AST construction problem??

Ric Klaren klaren at cs.utwente.nl
Mon Aug 4 04:06:06 PDT 2003

On Fri, Aug 01, 2003 at 07:34:34PM -0000, Fan Yang wrote:
> In order to be familiar with AST construction, I did some small tests 
> by usning ANTLR 2.7.2. I realized that ANTLR 2.7.2 can't generate code
> (in CPP or Java) correctly, but ANTLR 2.7.1 can. I don't know if I do 
> it in a wrong way or ANTLR 2.7.2 has a bug. Would you please point me 
> the problem. thanks.
> Here is the problem, I modified grammar of exprAST which exists 
> in "examples" directory of ANTLR. I use manual tree construction for 
> the rule instead of automatic one.
> expr! : 
> 	assignExpr EOF! 
                 ^- this is the culprit.
> 	{#expr = #(assignExpr, EOF);}
> 	;

Due to the '!' on EOF no AST return is generated (the tmp1_AST) if you
remove the !-operator the rule will work. It will also work if you label
teh EOF and use the label like this:

expr! :
 	assignExpr e:EOF!
 	{#expr = #(assignExpr, #e);}

In this case the labeling of the EOF overwrites the !-operator. Although it
would be nice if antlr gave a warning in such a case. Giving a warning for
the particular case you constructed could be tricky, but I'll see what I
can do.


    ---- Ric Klaren ----- j.klaren at utwente.nl ----- +31 53 4893722  ----
 "Don't call me stupid." "Oh, right. To call you stupid would be an insult
    to stupid people. I've known sheep that could outwit you! I've worn
              dresses with higher IQs!" --- A Fish Called Wanda


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