// run

// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

type Gen[A any] func() (A, bool)

func combine[T1, T2, T any](g1 Gen[T1], g2 Gen[T2], join func(T1, T2) T) Gen[T] {
    return func() (T, bool) {
        var t T
        t1, ok := g1()
        if !ok {
            return t, false
        }
        t2, ok := g2()
        if !ok {
            return t, false
        }
        return join(t1, t2), true
    }
}

type Pair[A, B any] struct {
	A A
	B B
}

func NewPair[A, B any](a A, b B) Pair[A, B] { return Pair[A, B]{a, b} }

func Combine2[A, B any](ga Gen[A], gb Gen[B]) Gen[Pair[A, B]] {
    return combine(ga, gb, NewPair(A, B))
}

func main() {
	var g1 Gen[int] = func() (int, bool) { return 3, true }
	var g2 Gen[string] = func() (string, bool) { return "x", false }
	gc := combine(g1, g2, NewPair[int, string])
	gc2 := Combine2(g1, g2)
	if got, ok := gc(); ok {
		panic(got)
	}
	if got2, ok := gc2(); ok {
		panic(got2)
	}
}