builtin: add :ne, inequality over two evaluated constants - #92
builtin: add :ne, inequality over two evaluated constants#92brian-slashguard wants to merge 1 commit into
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Mangle has :lt/:le/:gt/:ge but no not-equals, so every inequality must be written as negation over a domain the program derives first. That is a recurring authoring and review cost for a common construct. Adds :ne at the four registration points :lt uses — symbol, arg modes, decision case, and relation type. The relation type is the non-obvious one: without it the predicate parses and reaches evaluation, then fails type inference with 'cannot find assignment that works for premise :ne(A,B)', which reads like a broken implementation. Verified: differs(A,B) :- colour(A), colour(B), :ne(A,B) over three colours yields the six ordered pairs of distinct values.
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Hey there! First, an administrative remark: this project lives on codeberg now. I can review it here, but I'd prefer to not depend on github. Now, about the PR itself:
In fact, built-in predicates are specific to types - there should be a ":float:lt" etc for floats, but that was missing which I will add now. |
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Mangle has
:lt/:le/:gt/:gebut no not-equals, so every inequality must be written as negation over a domain the program derives first.This adds
:neat the same four registration points:ltuses: symbol declaration, arg modes, the decision case, and the relation type.The relation type is the non-obvious one — without it the predicate parses and reaches evaluation, then fails type inference with
cannot find assignment that works for premise :ne(A,B), which reads like a broken implementation rather than a missing registration.Verified:
differs(A,B) :- colour(A), colour(B), :ne(A,B).over three colours yields the six ordered pairs of distinct values.go build ./...is clean.Happy to adjust naming or the type bound if you'd prefer something narrower than
AnyBound.