package main

import (
	"fmt"
	"strconv"
)

// Counterpart to Haskell's `derive Show` through code generation
//go:generate stringer -type parity

type parity int

const even parity = 0
const odd parity = 1

// shouldBe returns a function that returns true if an int is
// of the given parity
func shouldBe(p parity) func(i int) bool {
	return func(i int) bool {
		return i%2 == int(p)
	}
}

func main() {
	lst := []int{1, 2, 3, 4, 5}
	lstMult := fmap(
		func(i int) int { return i * 5 },
		prepend(0, lst),
	)

	addToString := func(s string, i int) string {
		return s + strconv.Itoa(i) + " "
	}

	// fold over even / odd numbers and add them to a string
	evens := foldl(addToString, even.String()+": ",
		filter(shouldBe(even), lstMult))

	odds := foldl(addToString, odd.String()+": ",
		filter(shouldBe(odd), lstMult))

	fmt.Println(evens, odds)
}