Monad in go

mm.go

package main

import (
	"fmt"
)

func f1(x int) (int, string) {

    return x + 1, fmt.Sprintf("%d+1", x)

}

func f2(x int) (int, string) {

    return x + 2, fmt.Sprintf("%d+2", x)

}

func f3(x int) (int, string) {

    return x + 3, fmt.Sprintf("%d+3", x)

}

type Increment func(y int) (int, string)

type Log struct {
	Val int
	Op string
}

func (l *Log) ToString() string {
	
	return fmt.Sprintf("Res: %d, Ops: %s", l.Val, l.Op)

}

func unit(x int) *Log {

    return &Log{Val: x, Op: ""}

}

func bind(x *Log, f Increment) *Log {

	val, op := f(x.Val)
    return &Log{Val: val, Op: fmt.Sprintf("%s%s; ", x.Op, op)}

}

func pipeline(x *Log, fs ...Increment) *Log {

	for _, f := range fs {
		x = bind(x, f)
	}
	return x

}

func first() {

	x := 0
	log := "Ops: "

	res, log1 := f1(x)
	log += log1 + "; "
	
	res, log2 := f2(res)
	log += log2 + "; "
	
	res, log3 := f3(res)
	log += log3 + "; "
	
	fmt.Printf("Res: %d, %s\n", res, log)

}

func second() {

	x := 0
	fmt.Printf("%s\n", bind(bind(bind(unit(x), f1), f2), f3).ToString())

}

func third() {

	x := 0
	fmt.Printf("%s\n", pipeline(unit(x), f1, f2, f3).ToString())

}

func main() {

	first()
	second()
	third()

}