🚀 go-pugleaf

In article <8205@pt.cs.cmu.edu> fp@PROOF.ERGO.CS.CMU.EDU (Frank Pfenning) writes:
>I am looking for papers/reports/code/information on "legitimate" uses
>of "assert" and "retract" in logic programming, that is, uses which are
>considered to be in good taste by the connoisseurs of the field.

Many of the best uses are for assert WITHOUT retract. They generally come into
the area of "lemmas": asserting things you've found to be true so you don't
have to prove them all over again. This is mentioned in Sterling and Shapiro
(The Art of Prolog) p.181 - section entitled "Memo Functions" with an example
of Towers of Hanoi.

(retract is used simply to clean up at the end)

Another example is the (bottom-up) chart parser in Rob Simmons' "Computations
from the English" p.202.  Here again the information is additive, because every
part of the well-formed substring table remains valid.


Chris Moss.