rescript-js-collections

bs-js-collections

Bindings to primitive JavaScript Set and Map types for BuckleScript/ReScript.

In addition to bindings to the native API, this library adds a number of functions useful for pure functional programming, such as:

• Conversion to/from various data structures such as arrays, lists, dicts and Belt data structures
• map, keep, reduce, including *WithKey versions for the Map type
• Set operations such as union, intersection and diff

It is largely influenced by Belt, following similar naming conventions and favoring fast-pipe argument order (i.e. significant-data-first).

Examples

Sets

// Construct empty, with a single element, or from an array
let myEmptySet = JsSet.empty();
let mySetWithOneString = JsSet.singleton("hello!");
let myIntSet = [|1, 2, 3|]->JsSet.fromArray;

// Mutably add some values to the set
[|3, 4, 5|]->Belt.Array.forEach(myIntSet->JsSet.addMut);

// Mutably delete values from the set
myIntSet->JsSet.deleteMut(1);

// Map functions over the set
let myStringSet = myIntSet->JsString.map(string_of_int);

// Filter the set
Js.log(myIntSet->keep(i => i < 3)); // { 1, 2 }

// Filter and map the set
Js.log(myIntSet->keepMap(i => i == 2 ? None : Some(i->string_of_int))); // { '1', '3' }

Js.log(myIntSet->JsSet.size); // 2

Maps

let myStringMap = JsMap.fromArray([|("x", 1), ("y", 2)|]);
myStringMap->JsMap.delete("x");
Js.log(myStringMap->JsMap.size); // 1
Js.log(myStringMap->JsMap.has("y")); // true
Js.log(myStringMap->Js.Map.get("y")); // 2

See the .rei files for more tails, and unit tests examples of usage. In general we try to follow naming conventions similar to Belt and a pipe-first style.

Usable types

One of the advantages of JsMap.t over Js.Dict.t is to allow arbitrary key types (e.g. numbers). Similarly for the values allowable in JsSet.t. The compiler will set values and map keys to be any type, but in practice only certain types will work. In particular, it must be a type at runtime that JavaScript is able to handle.

The rule of thumb is that for map keys and set values, it must be a type which, at runtime, takes the form of an int, a string, a boolean, etc. This means that most enums are fine, as are opaque wrapper types.

Do not use records, lists, arrays, tuples, etc.

Avoid optional types in general or at the least provide extra testing if it's unavoidable.

Commands/scripts

yarn re:build
yarn re:clean
yarn re:watch