[antlr-interest] Are token aliases possible?

[Christian]

If CLASS_DECL should only be another name with the same type, than, in
Java, it could be easily declared as another constant with the same value:

private final static int CLASS_DECL = CLASS;

However, ANTLR does not support it, at least not independent of the
target language.

Am 28.10.2011 16:38, schrieb Sam Barnett-Cormack:
> That looks a very handy feature. I wonder if there's any chance of it
> arriving in the Java version?
>
> Sam
>
> On 28/10/2011 14:50, Sam Harwell wrote:
>> In the Java version, the rewrite syntax is the definitive way to
>> specify the
>> type of a tree node.
>>
>> In the newer versions of the C# port, you can specify tree node types
>> as a
>> token option, so you could do this and be equivalent to your rewrite
>> rule.
>> Note that I added a ^ as well; your first example did not include it but
>> that's what makes a particular node the root of the created tree.
>> Since the
>> AST operators (^ and !) perform better in a number of ways than the
>> rewrite
>> operators, I added this feature to allow me to use AST operators in a
>> number
>> of places where I previously used rewrite syntax for the sole purpose of
>> changing a node type.
>>
>> class_declaration
>>    : CLASS<CLASS_DECL>^  type_or_generic   class_base?
>> type_parameter_constraints_clauses?   class_body   ';'!?
>>
>>
>> -----Original Message-----
>> From: antlr-interest-bounces at antlr.org
>> [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Christian
>> Sent: Friday, October 28, 2011 6:46 AM
>> To: antlr-interest at antlr.org
>> Subject: Re: [antlr-interest] Are token aliases possible?
>>
>> Yes, I know that one can use rewrite rules. Thank you anyway. In some
>> cases
>> however, I do not want to repeat the rules following the CLASS token and
>> write an arrow etc. In such cases, it is shorter to just replace the
>> CLASS
>> by CLASS_DECL and add a few operators instead of a rewrite rule.
>>
>> As an example, I want to transform the following rule:
>>
>> class_declaration
>>    : CLASS  type_or_generic   class_base?
>> type_parameter_constraints_clauses?   class_body   ';'?
>>
>> into
>>
>> class_declaration
>>    : CLASS_DECL  type_or_generic   class_base?
>> type_parameter_constraints_clauses?   class_body   ';'!?
>>
>> versus
>>
>> class_declaration
>>    : CLASS  type_or_generic   class_base?
>> type_parameter_constraints_clauses?   class_body   ';'?
>>        ->  ^(CLASS_DECL type_or_generic class_base?
>> type_parameter_constraints_clauses? class_body)
>>      ;
>>
>> I think everyone, especially me, would prefer the first solution.
>>
>> Am 28.10.2011 13:34, schrieb Sam Barnett-Cormack:
>>> I don't know for sure, buut my immediate thought is that it isn't
>>> likely to be possible (as tokens are generated without reference to
>>> parse context, and must be unambiguous except where code manually
>>> deals with the ambiguity). You could however create it as a dummy
>>> token name, and rewrite to it in the parser, such that the AST
>>> generated has a 'virtual' CLASS_DECL token generated from the 'real'
>>> CLASS token. Pretty sure there are examples of this in the wiki.
>>>
>>> On 28/10/2011 12:27, Christian wrote:
>>>> CLASS is only the token name. However, CLASS_DECL represents the
>>>> semantics of what was parsed. It allows to be more consequent when
>>>> analyzing the generated AST by names like CLASS_DECL, METHOD_DECL,
>>>> FIELD_DECL etc.
>>>>
>>>> Example:
>>>>
>>>> switch (node.getType()) {
>>>>      case CsRewriteRulesParser.NAMESPACE_DECL:
>>>>         // TODO
>>>>         break;
>>>>      case CsRewriteRulesParser.METHOD_DECL:
>>>>         // TODO
>>>>         break;
>>>>      case CsRewriteRulesParser.CLASS_DECL:
>>>>         // TODO
>>>>         break;
>>>> }
>>>>
>>>> It would be just another name for the integer constant CLASS.
>>>>
>>>> Am 28.10.2011 13:19, schrieb Sam Barnett-Cormack:
>>>>> I think the immediate answer is, "why?"
>>>>>
>>>>> On 28/10/2011 09:02, Christian wrote:
>>>>>> Hi community,
>>>>>>
>>>>>> if there is a real token, say
>>>>>>        CLASS : 'class';
>>>>>> can a define an alias, say
>>>>>>        CLASS_DECL = CLASS
>>>>>> in some way?
>>>>>>
>>>>>> Regards,
>>>>>> Christian
>>>>>>
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>>>>>> ess
>>>>>
>>>>
>>>>
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>>>
>>
>>
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