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Computation of FIRST set
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| Ulrich Frank 2006-02-19, 3:56 am |
| 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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| Ulrich Hobelmann 2006-02-19, 7:00 pm |
| Ulrich Frank wrote:
> 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?!!
Yes.
> And if I define rule1 as
>
> rule1 = (ID)? rule2;
>
> which is equivalent to the first rule1 definition, FIRST(rule1) also is
> {ID, "where"} RIGHT?!!
Yes to both.
> Please say, that I'm right. Thanks.
Looks very much like it, yes. No need to be  . ;)
--
Suffering from Gates-induced brain leakage...
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