95 lines
2.5 KiB
TypeScript
95 lines
2.5 KiB
TypeScript
type Mapper<T, U> = (x: T) => U;
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declare function wrap<T, U>(cb: Mapper<T, U>): Mapper<T, U>;
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declare function arrayize<T, U>(cb: Mapper<T, U>): Mapper<T, U[]>;
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declare function combine<A, B, C>(f: (x: A) => B, g: (x: B) => C): (x: A) => C;
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declare function foo(f: Mapper<string, number>): void;
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let f1: Mapper<string, number> = s => s.length;
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let f2: Mapper<string, number> = wrap(s => s.length);
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let f3: Mapper<string, number[]> = arrayize(wrap(s => s.length));
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let f4: Mapper<string, boolean> = combine(wrap(s => s.length), wrap(n => n >= 10));
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foo(wrap(s => s.length));
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let a1 = ["a", "b"].map(s => s.length);
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let a2 = ["a", "b"].map(wrap(s => s.length));
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let a3 = ["a", "b"].map(wrap(arrayize(s => s.length)));
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let a4 = ["a", "b"].map(combine(wrap(s => s.length), wrap(n => n > 10)));
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let a5 = ["a", "b"].map(combine(identity, wrap(s => s.length)));
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let a6 = ["a", "b"].map(combine(wrap(s => s.length), identity));
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// This is a contrived class. We could do the same thing with Observables, etc.
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class SetOf<A> {
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_store: A[];
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add(a: A) {
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this._store.push(a);
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}
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transform<B>(transformer: (a: SetOf<A>) => SetOf<B>): SetOf<B> {
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return transformer(this);
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}
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forEach(fn: (a: A, index: number) => void) {
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this._store.forEach((a, i) => fn(a, i));
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}
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}
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function compose<A, B, C, D, E>(
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fnA: (a: SetOf<A>) => SetOf<B>,
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fnB: (b: SetOf<B>) => SetOf<C>,
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fnC: (c: SetOf<C>) => SetOf<D>,
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fnD: (c: SetOf<D>) => SetOf<E>,
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):(x: SetOf<A>) => SetOf<E>;
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/* ... etc ... */
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function compose<T>(...fns: ((x: T) => T)[]): (x: T) => T {
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return (x: T) => fns.reduce((prev, fn) => fn(prev), x);
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}
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function map<A, B>(fn: (a: A) => B): (s: SetOf<A>) => SetOf<B> {
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return (a: SetOf<A>) => {
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const b: SetOf<B> = new SetOf();
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a.forEach(x => b.add(fn(x)));
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return b;
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}
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}
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function filter<A>(predicate: (a: A) => boolean): (s: SetOf<A>) => SetOf<A> {
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return (a: SetOf<A>) => {
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const result = new SetOf<A>();
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a.forEach(x => {
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if (predicate(x)) result.add(x);
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});
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return result;
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}
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}
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const testSet = new SetOf<number>();
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testSet.add(1);
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testSet.add(2);
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testSet.add(3);
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const t1 = testSet.transform(
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compose(
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filter(x => x % 1 === 0),
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map(x => x + x),
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map(x => x + '!!!'),
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map(x => x.toUpperCase())
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)
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)
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declare function identity<T>(x: T): T;
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const t2 = testSet.transform(
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compose(
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filter(x => x % 1 === 0),
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identity,
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map(x => x + '!!!'),
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map(x => x.toUpperCase())
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)
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)
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