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Path: utzoo!linus!decvax!harpo!eagle!mhuxl!ihnp4!arizona!budd
From: budd@arizona.UUCP (tim budd)
Newsgroups: net.lang.st80
Subject: st80 grammar ambiguous
Message-ID: <7335@arizona.UUCP>
Date: Sat, 14-Jan-84 22:32:50 EST
Article-I.D.: arizona.7335
Posted: Sat Jan 14 22:32:50 1984
Date-Received: Sun, 15-Jan-84 20:25:46 EST
Organization: CS Dept, U of Arizona, Tucson
Lines: 18


        Has anybody else noticed that the grammar for smalltalk given
in the Goldberg book is ambiguous?  The problem is that a message
pattern of the keyword type ( (keyword variable)* ) can look an awful lot
like the continuation of a previous message.  ie, one could write


        receiver kw1: arg1 kw2: arg2

     NextMessage: arg

Where NextMessage is the start of the next message description.  However,
it could also be considered part of the command being given to ``receiver''.
This makes writing a parser for ST-80, say using YACC (which is how I
discovered this problem) rather difficult.

Does anybody know how this problem is avoided in actual systems?

--tim budd - university of arizona - {kpno, ucbvax} ! arizona ! budd