Re: dynamic yacc-tables?

In article 91-08-043 canver@cyborg.informatik.uni-ulm.de (Ercument Canver) writes:
>I got the following problem: I need to extend the parse tables generated
>by yacc dynamically during parsing a text. ...
>
>Background: I'm posting this request because I have to write a parser suitable
>for declaring mixfix operators and overloading.
>
>I'd also appreciate pointers to parser generaters dealing with this kinda
>problem (not necessarily yacc-like).


You may want to attack the problem with lex instead of yacc. Read:
PARSING DISTFIX OPERATORS by Edgar H. Sibley in Commmunications of the ACM
February 1986, Vol 29, num 2, page 118.
Abstract:
        The advantages of user-defined distfix operators -- a syntactic
        convenience that enhances the readability of programs -- can be
        obtained as an extension of almost any programming language without
        requiring dynamic changes to the parser.
Conclusions:
        We have described a simple technique whereby a fixed BNF grammar can
        describe languages including user-defined infix, postfix, and distfix
        operators. The technique requires only that the parts of disfix
        operators be lexically distinguishable. ...
        The idea has been successfully implemented [with YACC] with minimal
        effort.


Note that "lexically distinguishable" means that lex can look up the
answer in a table, which can grow dynamically. I'm not sure how Sibley's
ideas interact with overloading.


Joshua Levy (joshua@veritas.com)
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