[Date Prev] [Date Next] [Thread Prev] [Thread Next] Date Index Thread Index Search archive:
Date:Mon Nov 2 18:21:52 1999 
Subject:news-relayFrom: pop@roo.cs.umass.edu (Robin Popplestone) 
From:PP User 
Volume-ID:991102.03 

Note that "unification" as implemented in Prolog is NOT unification as
understood by logicians, since the "occurs check" is not performed.
This check is a significant complication of the algorithm, and has
significant cost (see my rendering of A&S just posted).

The ML'ers must have done a unification with an occurs check
for SML in Poplog, though I doubt if their code is general-purpose, dealing
as it does with unification of SML type structures. Failure of the occurs
check is manifest by the distressing message "unification failure - cyclic
type structure".

Robin.