[antlr-interest] Are token aliases possible?

[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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>>>>
>>>
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>>
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