I’am a bit confused with undo/1. I’ve found that it is being executed even if I specify !/0 after it. To my reasoning it shouln’t. Consider this example: test1 :- writeln("+"), undo(writeln("-")), !. When I run it I get: ?- test1. + true. - Why undo goal is executed? How to prevent it from being…

The undo/1 predicate is called on backtracking, using the same semantics as for unbinding a variable on backtracking. Compare ?- (A = b, fail ; write(A)). _57118 ?- dynamic p/1. ?- (assert(p(1), Ref), undo(erase(Ref)), fail ; \+ p(1))). true. % i.e., p(1) is removed Note that the toplevel REP…

Undo/1 and !/0

General

abaljeu June 15, 2022, 4:56pm 4

Is undo/1 new? I don’t remember ever encountering this before. (Aside: it would be neat if tiny text on each doc page stated when that was added/last updated.)

It is useful to try and capture the story of a predicate or a feature in the docs?

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Undo/1 and !/0

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