Re: no reserved words

William D Clinger <will@ccs.neu.edu>
15 Mar 1998 00:19:53 -0500

          From comp.compilers
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no reserved words hugo@morantek.demon.co.uk (1998-03-08)
Re: no reserved words cfc@world.std.com (Chris F Clark) (1998-03-12)
Re: no reserved words leichter@smarts.com (Jerry Leichter) (1998-03-13)
Re: no reserved words will@ccs.neu.edu (William D Clinger) (1998-03-15)
Re: no reserved words stephen@acm.org (Stephen P Spackman) (1998-03-18)
Re: no reserved words sandeep.dutta@usa.net (Sandeep Dutta) (1998-03-18)
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From: William D Clinger <will@ccs.neu.edu>
Newsgroups: comp.compilers
Date: 15 Mar 1998 00:19:53 -0500
Organization: Northeastern University
References: 98-03-091
Keywords: yacc, parse, comment

When parsing a language with no reserved words, the following trick
might allow you to use Lex and Yacc or similar tools.


Use Lex to define a token (e.g. IF, THEN, CALL) for each syntactic
keyword of the language. Also define a token NONKEYWORD for
identifiers that are not also reserved words.


Use yacc to define a nonterminal identifier as follows:


        identifier : NONKEYWORD
                              | IF
                              | THEN
                              | CALL
                              | ...


Then use the nonterminal identifier wherever you want to allow any
identifier, and use the specific tokens IF, THEN, et cetera wherever a
specific syntactic keyword must go.


You might have to resolve a lot of shift-reduce and reduce-reduce
conflicts, but those conflicts are sort of intrinsic to the grammar of
your language; you'll have to resolve them somehow no matter what
tools you use.


Will
[See subsequent message about ambiguity problems. -John]
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