Created
October 15, 2020 16:02
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monocle-ts traversal example
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| import * as T from "monocle-ts/lib/Traversal"; | |
| import * as R from "fp-ts/lib/Record"; | |
| import { pipe } from "fp-ts/lib/function"; | |
| import { Lens } from "monocle-ts"; | |
| type Person = { | |
| age: number; | |
| hairColor: string; | |
| }; | |
| //normal Lens | |
| const PersonL = Lens.fromProp<Person>(); | |
| const HairColorL = PersonL("hairColor"); | |
| /** | |
| * Traverse all the Person in Record<string, Person> | |
| * Reaching to the .hairColor via the Lens above | |
| * only if the .page > 70 (this is the cool part) | |
| */ | |
| const traverseRecordPerson = pipe( | |
| T.fromTraversable(R.record)<Person>(), | |
| T.filter((person) => person.age > 70), | |
| T.compose(HairColorL.asTraversal()) | |
| ); | |
| const setOldPplToWhiteHair = pipe( | |
| traverseRecordPerson, | |
| T.modify((hairColor) => "white") | |
| ); | |
| const ppl: Record<string, Person> = { | |
| david: { age: 71, hairColor: "brown" }, | |
| max: { age: 26, hairColor: "brown" } | |
| }; | |
| const result = setOldPplToWhiteHair(ppl); | |
| console.log(result); |
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