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From: joshua@Atherton.COM (Joshua Levy)
Newsgroups: comp.compilers
Subject: Re: Looking for dynamic parser generator
Keywords: parse, interpreter, yacc
Message-ID: <34658@joshua.athertn.Atherton.COM>
Date: 7 Mar 91 19:32:59 GMT
References: <18231@cs.utexas.edu>
Sender: compilers-sender@iecc.cambridge.ma.us
Reply-To: joshua@Atherton.COM (Joshua Levy)
Organization: Atherton Technology, Sunnyvale, CA
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In article <18231@cs.utexas.edu> turpin@cs.utexas.edu (Russell Turpin) writes:
>I am interested in any parser generators ... that one can, at run time, 
>parse strings from many languages and also define new languages.  ...
>
>I doubt this can be done with yacc and lex.

Ye of little faith! :-)  Read "Parsing Distfix Operators" in CACM Feb. 1986
(Vol 29, #2) by Simon L. Peyton Jones on page 118.  To quote the summary:

    We have described a simple technique whereby a fixed BNF grammar can 
    describe languages including user defined infix, postfix, and disfix 
    operators.  The technique requires only that the parts of disfix operators
    be lexically distinguishable.  Standard parser generators can then produce
    efficient parsers for such grammars ...  The idea has been successfully
    implemented with minimal effort.

The paper is only 5 pages long, easy to understand, and includes some
sample code.  They use YACC as their "standard parser generator".  Note
the limitation of the method: certain tokens must be lexically
distinguishable.  I doubt this solves your whole problem, but I think
it solves part of it.

Joshua Levy   (joshua@atherton.com)   408-734-9822

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