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From: slv@seg.npl.co.uk (S Voogd)
Newsgroups: comp.compilers
Subject: yacc first and follow set generator wanted
Keywords: yacc, question
Message-ID: <2390.9011081700@lemon.seg.npl.co.uk>
Date: 8 Nov 90 17:00:31 GMT
Sender: compilers-sender@iecc.cambridge.ma.us
Reply-To: S Voogd <slv@seg.npl.co.uk>
Organization: Compilers Central
Lines: 38
Approved: compilers@iecc.cambridge.ma.us

'allo, 'allo,

I require a program that, given the syntax of a language written in YACC,
will give a list of all tokens that can appear immediately to the right of
some given non_terminal and a list of all tokens that can appear as the
first token of that non-terminal. (The so-called FIRST and FOLLOW sets)

Maybe it is possible to derive those sets from YACC (YACC uses those sets
to fill the parse-table) but I could not find anything about it in the
manual or other books (e.g. Aho, Sethi, Ullman).

Maybe FIRST and FOLLOW sets are called otherwise elsewhere therefore I'll
explain what I mean with it.

Given the following grammar:

A :  B  'c'  D;
B : 'e' 'f'
  | 'g' 'h';
C :  B  'i';
 
The First set of A is First(A) = First(B) = {'e', 'g'}
The FOLLOW set of B is Follow(B) = {'c', 'i'}


			Many thanx in advance
			       SIMON

please send replies to : slv@seg.npl.co.uk
			 S. L. Voogd
			 NPL London UK
			 +81 - 943 7009
				   6994
[I'd think one would be able to extract the info from the y.output listing,
or else directly from the generated parse tables. -John]
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