Computation of FIRST set

"Ulrich Frank" <franku@fmi.uni-passau.de>
19 Feb 2006 02:01:45 -0500

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Computation of FIRST set franku@fmi.uni-passau.de (Ulrich Frank) (2006-02-19)
Re: Computation of FIRST set u.hobelmann@web.de (Ulrich Hobelmann) (2006-02-19)
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From: "Ulrich Frank" <franku@fmi.uni-passau.de>
Newsgroups: comp.compilers
Date: 19 Feb 2006 02:01:45 -0500
Organization: http://groups.google.com
Keywords: LL(1), question
Posted-Date: 19 Feb 2006 02:01:45 EST

Hello NG,


I have a big problem with ANTLR and the computation of the first set of
a rule. I've already read corresponing articles on the computation of
the first set but additionally want to ask you.


In the lexer I define a token ID : ('a'..'z'); and in the parser I have
the following rules:


rule1 = ID rule2 | rule2;
rule2 = "where" rule3;
rule3 ...


So FIRST(rule1) = {ID, "where"} and FIRST(rule2) = {"where"}
RIGHT?!!


And if I define rule1 as


rule1 = (ID)? rule2;


which is equivalent to the first rule1 definition, FIRST(rule1) also is
{ID, "where"} RIGHT?!!


Please say, that I'm right. Thanks.

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