[antlr-interest] Understanding error: Label 'XX' has already been defined

[Terence Parr]

On Monday, September 23, 2002, at 01:59  PM, namidsf wrote:

> Hi relatives in trade,
>
> I posted the following question on jGuru a few days ago and got
> prompt answer from Monty (thanks again). Sounds like ultimate
> solution will require work in the Code Generator.
>
> I still hope to find somebody who ran into similar behaviour
> and may have some ideas on the grammar level ...
> The following is my original message to jGuru:

The issue is that labels are used for exceptions too and hence must be 
unique per method so that you can specify a catch on one of those 
labels.  Or am I confusing myself with PCCTS.  Hmm....haven't looked at 
that in a while.  It's probably also an issue of where the labels are 
defined.

Ter

> ---------------------------------------------------------
> There is an existing grammar file (lets say My.g) - that was
> originaly processed with Antlr 2.6.1.
> I'm working on upgrade of the grammar, but prior to appending
> grammar I would like to  recompile My.g with latest Antlr 2.7.2A2
> But there are number of errors:
>
>    "My.g:###:##: Label 'a' has already been defined.
>     Exiting due to errors."
>
> in all rules of the following nature: (skinned)
>
> CaseNodes returns [CMyNode *pNode]
>     {  pNode = NULL ; }
>     :
>     "null"      { pNode = new CMyNode(CMyNode::Null); }
>     |a:CASE1   { pNode = new CMyNode(CMyNode::case1); }
>     |a:CASE2   { pNode = new CMyNode(CMyNode::case2); }
>     |a:CASE3   { pNode = new CMyNode(CMyNode::case3); }
>     |a:DEFAULT { pNode = new CMyNode(CMyNode::dflt ); }
>     . . .
>     { pNode->t_ = a;  }
> ;
>
> I figured if I modify this rule to be:
>
> CaseNodes returns [CMyNode *pNode]
>     {  pExpr = NULL ; }
>     :
>     "null"    {pNode = new CMyNode(CMyNode::Null); }
>     |a:CASE1  {pNode = new CMyNode(CMyNode::case1); pNode->t_ = a; }
>     |a1:CASE2 {pNode = new CMyNode(CMyNode::case2); pNode->t_ = a1;}
>     |a2:CASE3 {pNode = new CMyNode(CMyNode::case3); . . .}
>     |a3:DEFAULT{pNode = new CMyNode(CMyNode::dflt ); . . .}
>     . . .
> ;
> errors are gone , but this will trigger lots of changes in the
> existing grammar file, and can be are very messy.
>
> What is the reason to changes in labels-related code generation
> (in 2.7) ? Is there is another way to approach it ?
>
> Thank you,
>
> Dmitriy Neyman
>
>
>
>
>
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>
--
Co-founder, http://www.jguru.com
Creator, ANTLR Parser Generator: http://www.antlr.org
Lecturer in Comp. Sci., University of San Francisco


 

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