reason-selector

GADT based reimplementation of reselect in ReasonML.

reason-selector is a re-imagining of the types used by reselect, such that the number of selects you pass to the create function has to equal the number of parameters of the callback given to create. The benefit is that it is not necessary to create verbose/redundant/error prone repetition in the bindings. It achieves this by using GADTs to generate the expected callback function type from the composition of the selects you provide.

The implementation is pure ReasonML, so this library could in theory be used by projects targeting native compilation targets.

Example

type item = {
  name: string,
  value: float,
};
type shop = {
  taxPercent: float,
  items: array(item),
};
type state = {shop};

let shopItemsSelector = state => state.shop.items;
let taxPercentSelector = state => state.shop.taxPercent;

let subtotalSelector =
  Selector.(
    create(
      select(shopItemsSelector),
      items => Array.fold_left((acc, item) => acc +. item.value, 0.0, items)
    )
  );

let taxSelector =
  Selector.(
    create(
      select(subtotalSelector) =>> select(taxPercentSelector),
      (subtotal, taxPercent) => subtotal *. (taxPercent /. 100.0)
    )
  );

type total = {total: float};

let totalSelector =
  Selector.(
    create(
      select(subtotalSelector) =>> select(taxSelector),
      (subtotal, tax) => {total: subtotal +. tax}
    )
  );

let exampleState = {
  shop: {
    taxPercent: 8.0,
    items: [|{name: "apple", value: 1.20}, {name: "orange", value: 0.95}|],
  },
};

Js.log(subtotalSelector(exampleState)); // 2.15
Js.log(taxSelector(exampleState)); // 0.172
Js.log(totalSelector(exampleState)); // { total: 2.322 }

Installation

npm install --save reason-selector

Then add reason-selector to bs-dependencies in your bsconfig.json:

{
  ...
  "bs-dependencies": ["reason-selector"]
}

Usage

See usage examples in the tests. The source is a single file that implements the simple Cache module and the selector create and composition operators select and =>>.

Changes

0.2.0

• Enforce the reverse Cons structure by using another type parameter and phantom types

0.1.0

• Initial release