Silly Go–with–generics (FGG) program to demonstrate the syntax.

silly.go2

package main

import "fmt"

func Fold(type T, U)(acc T, f func(T, U) T, xs []U) T {
	for _, x := range xs {
		acc = f(acc, x)
	}
	
	return acc
}

func Map(type T, U)(xs []T, f func(T) U) []U {
	ys := make([]U, 0, len(xs))
	ys = Fold(ys, func(acc []U, x T) []U { return append(acc, f(x)) }, xs)
	
	return ys
}

func Filter(type T)(xs []T, f func(T) bool) []T {
	ys := make([]T, 0, len(xs))
	ys = Fold(
		ys,
		func(acc []T, x T) []T { if f(x) { return append(acc, x) } else { return acc } },
		xs,
	)
	if len(ys) != len(xs) {
		ys = ys[:len(ys):len(ys)]
	}
	
	return ys
}

func main() {
	incremented := Map([]int{1,2,3}, func(x int) int { return x + 1})
	filtered := Filter(incremented, func(x int) bool { return x % 2 == 0 })
	summed := Fold(0, func(acc int, x int) int { return acc + x }, filtered)
	fmt.Println(incremented, filtered, summed)
}