Losing generics (composition/currying) #12838

declare function inc(n: number): number; // +1
declare function identity<T>(a: T): T;
declare function compose<V0, T1>(fn0: (x0: V0) => T1): (x0: V0) => T1;
declare function compose<V0, T1, T2>(fn1: (x: T1) => T2, fn0: (x: V0) => T1): (x: V0) => T2;
declare function pipe   <V0, T1>(fn0: (x0: V0) => T1): (x0: V0) => T1;                           // arity 1: same as compose
declare function pipe   <V0, T1, T2>(fn0: (x: V0) => T1, fn1: (x: T1) => T2): (x: V0) => T2;     // arity 2: params swapped

// don't use generics if it can't resolve them right away:
compose(identity) // generics lost, now {} => {}
pipe   (identity) // ditto
// argument order apparently matters too:
pipe   (inc, identity); // ok, number -> number
compose(identity, inc); // nope, number => {}
// also no reasoning backward:
compose(inc, identity); // {} => number
pipe   (identity, inc); // {} => number