Some initial work on monads in Golang

monad.go

package monad

type ThenCallback func(interface{}) (Thenable, error)

type Thenable interface {
  Then(ThenCallback) Thenable
  Unwrap() interface{}
}

type Error struct {
  err error
}

func (e Error) Content() error {
  return e.err
}

func (e Error) Then(f ThenCallback) Thenable {
  return e
}

func (e Error) Unwrap() error {
  return nil
}

type Unit struct {
  value interface{}
}

func (t Unit) Then(f ThenCallback) Thenable {
  value, err := f(t.Unwrap())
  if err != nil {
    return Error{err}
  }
  return Unit{value.Unwrap())
}

func (t Unit) Unwrap() interface{} {
  return t.value
}