Created
June 5, 2017 18:16
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Typescript Functional Lens
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interface MyStructure { | |
a: boolean; | |
b: number; | |
c: string; | |
d: { | |
e: boolean; | |
f: number; | |
g: string[]; | |
} | |
} | |
type Lensed<R, T> = { | |
<M extends keyof T>(member: M) : Lensed<R, T[M]> | |
read(root: R): T | |
write(root: R, value: T): R | |
} | |
function Lens<R>() : Lensed<R, R> { | |
function makeLens<R, P, M extends keyof P>(parent : ((root : R) => P), selfMember : M) : Lensed<R, P[M]> { | |
let lens: any = <N extends keyof P[M]>(member: N): Lensed<R, P[M][N]> => { | |
let selfAccessor = (root: R) => parent(root)[selfMember]; | |
return makeLens(selfAccessor, member); | |
}; | |
lens.read = (root: R): P[M] => parent(root)[selfMember]; | |
lens.write = (root: R, value: P[M]): R => { | |
let newRoot = JSON.parse(JSON.stringify(root)); | |
parent(newRoot)[selfMember] = value; | |
return Object.freeze(newRoot); | |
} | |
return <Lensed<R, P[M]>>lens; | |
} | |
let rootLens: any = <M extends keyof R>(member: M): Lensed<R, R[M]> => makeLens<R, R, M>(root => root, member); | |
rootLens.read = (root: R): R => root; | |
rootLens.write = (value: R): R => value; | |
return rootLens; | |
} | |
var lens = Lens<MyStructure>(); | |
var test: MyStructure = { | |
a: false, | |
b: 3, | |
c: 'Blah', | |
d: { | |
e: true, | |
f: 42, | |
g: [] | |
} | |
}; | |
lens.read(test); | |
lens.write(test, test); | |
var getted = lens('d')('f').read(test); | |
var setted = lens('d')('f').write(test, 5); | |
var setted2 = lens('d')('g').write(setted, ['', '']); | |
console.log(setted2); |
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