Notes on computational linguistics.pdf - UCLA Department of ...

Stabler - Lx 185/209 2003
(48) We can compute the bottom-up k = 1 words of lookahead offline:
| ?- [’la-sics’].
yes
| ?- [’g1-lc’].
yes
| ?- computela.
Warning: abolish(user:la) - no matching predicate
..........:.:.:.:.::.::.::.:.:.:.:.:.::.:.:.:.
yes
| ?- listing(la).
la([idea], idea).
la([idea], n0).
la([idea], n1).
la([idea], np).
la([suffice], suffice).
la([suffice], v0).
la([suffice], v1).
la([suffice], vp).
la([that], c0).
la([that], c1).
la([that], cp).
la([that], that).
la([the], d0).
la([the], d1).
la([the], dp).
la([the], ip).
la([the], the).
la([will], i0).
la([will], i1).
la([will], will).
yes
| ?-
(49) Adding bottom-up k-symbol lookahead to the glco recognizers with a bottom-up oracle, we have
glcola(k) recognizers.
For any of the GLC parsers, a language is said to be glcola(k) iff there is at most one step that can be
takenateverypointineveryproof.
Obviously, when a language has genuine structural ambiguity – more than one successful parse for
some strings in the language – the language cannot be glcola(k) for any k (e.g. LL(k), LC(k), LR(k),…)
In the case of an ambiguous language, though, we can consider whether the recognition of unambiguous
strings is deterministic, or whether the indeterminism that is encountered is all due to global ambiguities.
We return to these questions below.
95