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(.module:
[library
[lux #*]]
[//
["." equivalence (#+ Equivalence)]
[functor
["." contravariant]]])
(interface: .public (Hash a)
{#.doc (example "A way to produce hash-codes for a type's instances."
"A necessity when working with some data-structures, such as dictionaries or sets.")}
(: (Equivalence a)
&equivalence)
(: (-> a Nat)
hash))
(implementation: .public functor
(contravariant.Functor Hash)
(def: (map f super)
(implementation
(def: &equivalence
(\ equivalence.functor map f
(\ super &equivalence)))
(def: hash
(|>> f (\ super hash))))))
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