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@j-keck
Created November 15, 2014 08:20
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from: http://play.golang.org/p/P5DDZrcXZB
package main
import "fmt"
type Monad interface {
Bind(func(interface{}, Monad) Monad) Monad
Return(interface{}) Monad
}
// First, let's do Maybe
type Maybe struct {
val *interface{}
}
var None = Maybe{nil}
func Some(a interface{}) Monad {
return Maybe{&a}
}
func (m Maybe) Bind(f func(interface{}, Monad) Monad) Monad {
if m == None {
return None
}
return f(*m.val, m)
}
func (m Maybe) Return(a interface{}) Monad {
return Some(a)
}
func (m Maybe) String() string {
if m == None {
return "None"
}
return fmt.Sprintf("Some(%v)", *m.val)
}
// Let's do a slice of int!
type IntSliceMonad []int
func (m IntSliceMonad) Bind(f func(interface{}, Monad) Monad) Monad {
result := IntSliceMonad{}
for _, val := range m {
next := f(val, m).(IntSliceMonad)
result = append(result, next...)
}
return result
}
func (m IntSliceMonad) Return(a interface{}) Monad {
return IntSliceMonad{a.(int)}
}
func main() {
doubleMe := func(i interface{}, m Monad) Monad {
return m.Return(2 * i.(int))
}
tripleMe := func(i interface{}, m Monad) Monad {
return m.Return(3 * i.(int))
}
oops := func(i interface{}, m Monad) Monad {
return None
}
bothSigns := func(i interface{}, m Monad) Monad {
return IntSliceMonad{i.(int), -i.(int)}
}
fmt.Println(Some(5).Bind(doubleMe).Bind(tripleMe))
fmt.Println(Some(3).Bind(oops).Bind(doubleMe))
var oneTwoThree = IntSliceMonad{1, 2, 3}
fmt.Println(oneTwoThree.Bind(doubleMe).Bind(bothSigns))
}
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