[antlr-interest] parsing empty function parameters

[Jim Idle]

This tends to indicate that you have made a production with an empty alt,
also optional, akin to:

 

x    : arg? (COMMA arg?)* 

;

 

arg

     : expr

     | // Don’t do this

     ;

 

This may not be your exact problem but my bet is that it is something that
simplifies down to that.

 

Jim

 

From: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of Andy Tripp
Sent: Friday, October 05, 2007 1:40 PM
Cc: antlr-interest
Subject: Re: [antlr-interest] parsing empty function parameters

 

It should be that simple, but (at least with my grammar) when arg
can be empty, ANTLR bombs out.

Sohail Somani wrote: 

Isn't this just:
 
argList : arg (COMMA arg?)* ;
 
----- Original Message -----
Subject: [antlr-interest] parsing empty function parameters
Date: Fri, October 5, 2007 12:09
From: "Andy Tripp" HYPERLINK
"mailto:antlr at jazillian.com"<antlr at jazillian.com>
 
  

Using ANTLR v3.0.1,
I'm trying to parse function parameters which can be empty, like this:
f(a, , c, d);
g(,,,,)
 
I have:
argList
   : argSpec (COMMA argSpec)*
   ;
 
But then whenever I try to allow "argSpec" to have an empty alternative,
ANTLR itself
produces an OutOfMemoryError.
 
Here's the original "argSpec" rule, which doesn't allow empty:
 
argSpec
   : argPassingType? argSpec2
   ;
 
I tried making the whole thing optional:
argSpec
   : (argPassingType? argSpec2)?
   ;
 
I tried a syntactic predicate:
argSpec
   : (','|')') =>                // if next token is comma or rparen,
nothing to consume.
   | argPassingType? argSpec2
   ;
 
I tried a semantic predicate:
argSpec
   : {input.LT(1).getText().equals(",") ||
input.LT(1).getText().equals(")")}?
   | argPassingType? argSpec2
   ;
 
As I said, all these cause ANTLR to produce OutOfMemoryError, presumably
in an infinite loop matching this rule, but consuming no token.
Any suggestions?
 
 
 
    

 
  

 

 

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