Bad Golang Monads

bad_monad.go

package main

import (
	"errors"
	"fmt"
	"strings"
)

func main() {
	fmapOutcome, err := fmap(getName, isValidName)()
	fmt.Print("fmap valid: ", fmapOutcome, "\n")
	fmt.Print("fmap error: ", err, "\n")
	
	bindOutcome, err := bind(getName, pure(isValidName))()
	fmt.Print("bind valid: ", bindOutcome, "\n")
	fmt.Print("bind error: ", err, "\n")
}

func getName() (string, error) {
	apiCall := 4
	if apiCall > 3 {
		return "Elizabeth McDoodle", nil
	} else if apiCall > 2 {
		return "Liz", nil
	} else {
		return "", errors.New("apis are hard, ok!")
	}
}

func isValidName(name string) bool {
	return strings.Contains(name, "McDoodle")
}

func bind(g func() (string, error), f func(string) (bool, error)) func() (bool, error) {
	return func() (bool, error) {
		a, err := g()
		if err != nil {
			return false, err
		}
		return f(a)
	}
}

func pure(f func(string) bool) func(string) (bool, error) {
	return func(somestring string) (bool, error) {
		return f(somestring), nil
	}
}

func fmap(g func() (string, error), f func(string) bool) func() (bool, error) {
	return func() (bool, error) {
		a, err := g()
		if err != nil {
			return false, err
		}
		b := f(a)
		return b, nil
	}
}