Type inference in TypeScript for curried function
I have the following definition for a curried function in TypeScript:
interface Curried2<A, B, Z> {
(_0: A): (_0: B) => Z;
(_0: A, _1: B): Z;
}
I have the following function that should accept a function (curried or not):
function apply<T, U>(f: (_0: T) => U, x: T): U {
return f(x);
}
Now, given
let curried: Curried2<number, boolean, string> = ...
the following works (as expected):
apply<number, (_0: boolean) => string>(curried, 4);
But TypeScript cannot infer the type on its own:
apply(curried, 4);
(Even though there is only one overload for () which takes a single value.) It complains:
Argument of type 'Curried2<number, boolean, string>' is not assignable to parameter of type '(_0: number) => string' ...It has correctly inferred
T , but inferred U to be string . Why is this? What can I do to make type inference work for me in this case (as explicitly specifying T and U is too verbose for my taste)? Thanks in advance!
I could try this approach:
type Curried<T1, T2, T3> = (x: T1) => (y: T2) => T3;
function apply<T, U>(f: (value: T) => U, x: T): U {
return f(x);
}
//simple demo
var someFunc: Curried<string, number, [string, number]> = x => y => [x, y];
var curriedSomeFunc = apply(someFunc, "string here");
var result1 = curriedSomeFunc(0); //will be ["string here", 0]
var result2 = curriedSomeFunc(1); //will be ["string here", 1]
Another try. The syntax is correct but no safety if you pass not a correct function for currying:
interface Curried<T1, T2, T3> {
(x: T1, y: T2): T3;
(x: T1): (y: T2) => T3
}
let f1 = <Curried<string, number, [string, number]>>
((x: string, y: number) => [x, 1]);
let f2 = <Curried<string, number, [string, number]>>
((x: string) => (y: number) => [x, y]);
function apply<T, V>(f: (x: T) => V, x: T): V {
return f(x);
}
let curriedF1 = apply(f1, "42"); //Won't work (no function to curry) but type inference is OK
let curriedF2 = apply(f2, "11"); //Will work and type inference is also OK
以下现在工作：
interface F1<A, Z> {
(_0: A): Z;
}
interface F2<A, B, Z> extends F1<A, F1<B, Z>> {
(_0: A, _1: B): Z;
}
function apply<T, U>(f: F1<T, U>, x: T): U {
return f(x);
}
function apply2<T, U, V>(f: F2<T, U, V>, x: T, y: U): V {
return f(x, y);
}
let curried: F2<number, boolean, string> = null;
const x: F1<boolean, string> = apply(curried, 4);
const y: string = apply2(curried, 4, false);