err-monad.go

package errmonad

type ErrMonad[T any] struct {
	Val T
	Err error
}

type LiftFunc[T any] func(T) ErrMonad[T]

func Lift[T any](x T) ErrMonad[T] {
	return ErrMonad[T]{x, nil}
}

func (m ErrMonad[T]) Flatten() T {
	return m.Val
}

func (m ErrMonad[T]) FlatMap(f LiftFunc[T]) ErrMonad[T] {
	return f(m.Val)
}

func Compose[T any](fs ...LiftFunc[T]) LiftFunc[T] {
	return func(x T) ErrMonad[T] {
		var y ErrMonad[T]
		for i := len(fs) - 1; i >= 0; i-- {
			f := fs[i]
			y := f(x)
			x = y.Flatten()
		}
		return y
	}
}