map2.ts

export const map2 = function<UU extends URIS>(functor: Apply1<UU>) {
  return function<
    TypeUUA extends Type<UU, any>,
    TypeUUB extends Type<UU, any>,
    R
  >(
    fa: TypeUUA, fb: TypeUUB, f: (a: TypeUUA['_A'], b: TypeUUB['_A']) => R): Type<UU, R> {
      return functor.ap(
        functor.map(
          fa,
          a => (b: TypeUUB['_A']) => f(a, b)
        ),
        fb,
      )
  }
}