https://go2goplay.golang.org/p/DCHoOXmDuAs

generic.go

package main

type Optional(type T) struct {
	p *T
}

func OptionalFrom(type T)(value T) Optional(T) {
	return Optional(T){p: &value}
}

func (o Optional(T)) Val() (T, bool) {
	if o.p != nil {
		return *o.p, true
	}
	var zero T
	return zero, false
}

type Result(type T) struct {
	p   T
	err error
}

func ResultFrom(type T)(value T, err error) Result(T) {
	return Result(T){p: value, err: err}
}

func (o Result(T)) Val() (T, error) {
	if o.err != nil {
		var zero T
		return zero, o.err
	}

	return o.p, nil
}

type generic(type T) interface{}

type g(type T) interface {
	type T, generic(T)
}

func F(type
	V interface{},
	A g(V),
	B g(V),
)(o A, f func(A) B) B {
	return f(o)
}

func Print(type T g(T))(s []T) {
	for _, v := range s {
		// A(T) -> T
		_ = F(T, Optional(T), *T)(OptionalFrom(T)(v), func(o Optional(T)) (r *T) {
			return
		})

		// A -> B(T)
		_ = F(T, T, Result(T))(v, func(o T) (r Result(T)) {
			return
		})

		// A(T) -> B(T)
		_ = F(T, Optional(T), Result(T))(OptionalFrom(T)(v), func(o Optional(T)) (r Result(T)) {
			return
		})


		// A(T) -> C(B(T))
		_ = F(
			T,
			Optional(T),
			Optional(Result(T)),
		)(OptionalFrom(T)(v), func(o Optional(T)) (zero Optional( Result(T) ) ) {
			return
		})
	}
}

func main() {
	Print([]string{"Hello, ", "playground"})
}