module Summoner.Validation
       ( Validation (..)
       ) where

-- | 'Validation' is 'Either' with a Left that is a 'Monoid'
data Validation e a
    = Failure e
    | Success a
    deriving (Eq, Ord, Show)

instance Functor (Validation e) where
   fmap _ (Failure e) = Failure e
   fmap f (Success a) = Success (f a)

instance Semigroup e => Semigroup (Validation e a) where
    Failure e1 <> Failure e2 = Failure (e1 <> e2)
    Failure _  <> Success a2 = Success a2
    Success a1 <> Failure _  = Success a1
    Success a1 <> Success _  = Success a1

instance Semigroup e => Applicative (Validation e) where
    pure = Success

    Failure e1 <*> Failure e2 = Failure (e1 <> e2)
    Failure e1 <*> Success _  = Failure e1
    Success _  <*> Failure e2 = Failure e2
    Success f  <*> Success a  = Success (f a)