Ambiguous Grammar

[Ramaswamy]

Hi,

    I am working on a very ambiguous language. The language is ambiguous due to the support for complete forward referencing. Worst yet its meant to be user friendly which means its a headache for the compiler designers. Considering so many factorts and limited time available I choose to use the GLR parsing scheme provided by bison. On most ambiguous situations I am able to parse the input excepting on when the parser finds and ambiguity. Anyway this is as follows -

 

    Withing enclosed braces the following language is permitted -

 

TokenList:

      Token

    | TokenList Token

    ;

 

And the token is unfortunately as follows:

 

Token:

      A

    | B

    | C

    | and a lot more which r out of scope of the prblm

    ;

 

C: A B

 

    The actual grammar is not this elementary but I prefer presenting the base problem rather that giving other unwanted details. The language permits the tokens A & B in TokenList without any other tokens in b/w as in production C. The language specification says that there is no ambiguity, but due to forward referencing I face this problem. All I want to do is get the parser to go thru using any of the 2 ways of the following ambiguity for the input { ... A B ....}, preferably the one with the longer string -  

 

TokenList->

    TokenList->

        TokenList->... (before A)

        Token->A

    Token->B

 

and

 

TokenList->

    TokenList->... (before A)

    Token->C (with is an A followed by a B)

 

    I could not find out where in the grammar I should give the %dprec to let the grammar take the longer contineuous token (C). In case any of u can solve this problem or could give links to relavent links it would be great. Thanks in advance.

   

Regds
Ram
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