Attempt at monadic Go

m.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

type Result interface {
	unwrap() int
	String() string
}

type Success struct {
	value int
}

func (s Success) unwrap() int {
	return s.value
}

func (s Success) String() string {
	return strconv.Itoa(s.value)
}

type Failure struct {
	err string
}

func (s Failure) unwrap() int {
	panic("holy fuck")
}

func (s Failure) String() string {
	return "Error: " + s.err
}

type effectFnType func(int) (int, error)

func readAndAdd(prev int) (int, error) {
	print("Enter a number: ")
	in := bufio.NewScanner(os.Stdin)
	in.Scan()
	n, err := strconv.Atoi(in.Text())

	return n + prev, err
}

func bind(m Result, nextFn effectFnType) Result {
	switch m.(type) {
	case Failure:
		return m
	default:
		result, err := nextFn(m.unwrap())

		if err != nil {
			return Failure{err: err.Error()}
		} else {
			return Success{value: result}
		}
	}
}

func chain(init int, effects ...effectFnType) Result {
	result := bind(Success{value: init}, effects[0])

	for i := 1; i < len(effects); i++ {
		result = bind(result, effects[i])
	}

	return result
}

func main() {
	result := chain(0, readAndAdd, readAndAdd, readAndAdd)

	fmt.Println(result)
}