Elm archiceture introduced update : (message, state) => state, Redux reducers became standard in JS, but unlike Elm JS lacks pattern matching and flow's disjoint union refinements via switch statements require ton of boilerplate. This library attempts to provide a better solution via poor man's pattern matching for flow projects.
// @flow
import match from "match.flow"
const counter = match({
increment(_, n: number): number {
return n + 1
},
decrement(_, n: number): number {
return n - 1
}
})
counter({ increment: true }, 5) //? 6
counter({ decrement: true }, 5) //? 4
counter({}, 5) //?Probably the most compelling feature of this library is how it handlers error cases:
counter({ plus: 4 }, 3)Above line would cause flow to report error below, meaning you'll catch error before your code is ever run:
Error: Readme.js:4
v
4: const counter = match({
5: increment(_, n: number): number {
6: return n + 1
...:
11: })
^ object literal. This type is incompatible with the expected param type of
11: matcher: Matcher<model, message>
^^^^^^^^^^^^^^^^^^^^^^^ object type. See: src/match.js:11
Property `plus` is incompatible:
11: matcher: Matcher<model, message>
^^^^^^^^^^^^^^^^^^^^^^^ property `plus`. Property not found in. See: src/match.js:11
v
4: const counter = match({
5: increment(_, n: number): number {
6: return n + 1
...:
11: })
^ object literal
Found 1 error
Fixing that code is as simple as providing plus case:
const counter = match({
increment(_, n: number): number {
return n + 1
},
decrement(_, n: number): number {
return n - 1
},
plus(param: number, n: number): number {
return n + param
}
})
counter({ plus: 4 }, 3) //? 7You could also combine multiple operations into single message although execution order is not guaranteed:
counter({ plus: 4, decrement: true }, 2) //? 5npm install match.flow
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