[antlr-interest] Value passed to String based rule parameter has spaces inserted after commas.

[Benjamin Niemann]

Sam Ellis wrote:

> I've using ANTLR Version 3.0 (May 17, 2007). I have found that quoted
> strings passed to String-based rules in my grammar are having extra spaces
> inserted into the string when it appears in the generated parser code.
> Specifically, if the string in my grammar contains a comma, then a space
> is inserted after the comma in the resulting code. Here is an example:
> 
> grammar Fruit;
> 
> options {
>     language=Java;
> }
> 
> fruit[String allowedFruit]
>     :    NAME { System.out.println(allowedFruit);}
>     ;
> 
> bowl
>     : fruit["apple,orange"]
>     ;
> 
> NAME    :    ('a' .. 'z')+
>     ;
> 
> The code that is generated contains:
> 
>             // /Users/samellis/Fruit.g:12:7: ( fruit[\"apple,orange\"] )
>             // /Users/samellis/Fruit.g:12:7: fruit[\"apple,orange\"]
> ...
>             fruit("apple, orange");
> 
> So you can see that a space has appeared in the generated code (not in the
> comments though). Bug in ANTLR perhaps?

Not a bug, but a limitation. The contents of [...] is a comma seperated list
of code fragments of the target language. ANTLR does not know anything
about the structure of the target language, it just splits the list by
comma, replaces $ and % references and passes it to the code generation
template, which construct a method call suitable for the target language.

So what ANTLR sees is: a rule with two arguments '"apple' and 'orange"'.
This is passed to the template which generates something like 
<rule>([list of arguments, seperated by ", "]);
Hence the additional space.

There not much ANTLR can do without knowing how strings, types,
comments, ... look like in the target language - that it would need a
complete grammar of each target language, which would make things way more
difficult to implement.

So finally: to work around this limitation, use something like that:

bowl
    : { f = "apple,orange"; }
      fruit[f]
    ;

-- 
Benjamin Niemann
Email: pink at odahoda dot de
WWW: http://pink.odahoda.de/