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module Main where
import Data.Monoid
import Optional
import Test.QuickCheck
newtype First' a =
First' { getFirst' :: Optional a }
deriving (Eq, Show)
instance Monoid (First' a) where
mempty = First' Nada
mappend (First' Nada) x = x
mappend x _ = x
instance Arbitrary a => Arbitrary (First' a) where
arbitrary = frequency [ (1, return $ First' Nada)
, (1, fmap (First' . Only) arbitrary) ]
firstMappend :: First' a
-> First' a
-> First' a
firstMappend = mappend
type FirstMappend =
First' String
-> First' String
-> First' String
-> Bool
type FstId =
First' String -> Bool
monoidAssoc :: (Eq m, Monoid m) => m -> m -> m -> Bool
monoidAssoc a b c =
(a <> (b <> c)) == ((a <> b) <> c)
monoidLeftIdentity :: (Eq m, Monoid m) => m -> Bool
monoidLeftIdentity a = (mempty <> a) == a
monoidRightIdentity :: (Eq m, Monoid m) => m -> Bool
monoidRightIdentity a = (a <> mempty) == a
main :: IO ()
main = do
quickCheck (monoidAssoc :: FirstMappend)
quickCheck (monoidLeftIdentity :: FstId)
quickCheck (monoidRightIdentity :: FstId)
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