CODEWITHSUNDEEP
prolog
Tirafesi
Tirafesi

Reputation: 1479

Math inside predicate header

Is there a way to make this work?

add(X, X + 1)

input: add(1, Y).
expected output: Y = 2.
output: Y = 1+1.

Or is it only possible by doing this?

add(X, Y):- Y is X+1.

Upvotes: 1

Views: 83

Answers (1)

false
false

Reputation: 10142

Historically, there have been many attempts to provide this functionality. Let me give as early examples CLP(ℜ) (about 1986) or more recently Prolog IV. However, sooner or later, one realizes that a programmer needs a finer control about the kind of unification that is employed. Take as example a program that wants to differentiate a formula. In that situation an interpreted functor would not be of any use. For this reason most constraints ship today as some added predicates leaving functors otherwise uninterpreted. In this manner they also fit into ISO-Prolog which permits constraints as extensions.

From a programmer's viewpoint, an extension as yours would reduce the number of auxiliary variables needed, however, it also would require to interpret all terms to this end which produces a lot of extra overhead.

Upvotes: 3

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