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creating custom ReasonML comparable / hashable types that can be used with Bucklescript's Belt Hash/Map/Set types
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| /* | |
| ocaml src: https://bucklescript.github.io/bucklescript/api/Belt.html | |
| */ | |
| /* base type */ | |
| type intTuple = (int, int); | |
| /* hashable tuple */ | |
| module TupleHashable = Belt.Id.MakeHashable({ | |
| type t = intTuple; | |
| let hash = ((a, b): t) => { | |
| /* see: https://stackoverflow.com/a/13871379 */ | |
| let vA = a >= 0 ? 2 * a : -2 * a - 1; | |
| let vB = b >= 0 ? 2 * b : -2 * b - 1; | |
| let vC = (vA >= vB ? vA * vA + vA + vB : vA + vB * vB) / 2; | |
| a < 0 && b < 0 || a >= 0 && b >= 0 ? vC : -vC - 1 | |
| }; | |
| let eq = ((x0, y0): t, (x1, y1): t) => { | |
| x0 == x1 && y0 == y1 | |
| }; | |
| }); | |
| /* create hashset instance using hashable tuple */ | |
| let myHashSet = Belt.HashSet.make( | |
| ~id = (module TupleHashable), | |
| ~hintSize = 8 | |
| ); | |
| Belt.HashSet.add(myHashSet, (10, 10)) | |
| /* comparable tuple */ | |
| module TupleComparable = Belt.Id.MakeComparable({ | |
| type t = intTuple; | |
| let cmp = ((a0, a1), (b0, b1)) => { | |
| switch (Pervasives.compare(a0, b0)) { | |
| | 0 => Pervasives.compare(a1, b1) | |
| | c => c | |
| } | |
| }; | |
| }); | |
| /* map instance using hashable tuple */ | |
| let myMap = Belt.Set.make(~id=(module TupleComparable)); | |
| Belt.Set.add(myMap, (10, 10)); |
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