[antlr-interest] parsing empty function parameters

[Sohail Somani]

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" <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?
>
>
>