Return to the
comp.compilers page.
Search the
comp.compilers archives again.
| Related articles |
|---|
| Minding my Ps and Qs peter.r.wilson@boeing.com (Peter R. Wilson) (1999-02-15) |
| Re: Minding my Ps and Qs torbenm@diku.dk (Torben Mogensen) (1999-02-16) |
| Re: Minding my Ps and Qs paul.janssens@skynet.be (JPA) (1999-02-21) |
| From: | Torben Mogensen <torbenm@diku.dk> |
| Newsgroups: | comp.compilers |
| Date: | 16 Feb 1999 23:20:01 -0500 |
| Organization: | Compilers Central |
| References: | 99-02-067 |
| Keywords: | parse, LL(1) |
In comp.compilers you write:
>I got stuck on a term in the grammar that was of the form:
>1 t = { P | Q } P .
>That is, sentences consisting of any number of P and/or Q, followed by
>P. This is LL(oo) as written.
An LL(1) version of this can be obtained by left factoring. We first
eliminate the {} and |:
t -> P t
t -> Q t
t -> P
We then left factor and get
t -> P t'
t -> Q
t' -> t
t' ->
We can get this back in EBNF as
t -> P [t] | Q t
which is in LL(1) as required (assuming P and Q have disjoint FIRST
sets etc.)
Torben Mogensen (torbenm@diku.dk)
Return to the
comp.compilers page.
Search the
comp.compilers archives again.