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{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE DatatypeContexts #-}
module ShouldCompile where
data Trivial a = Trivial
deriving (Functor)
data Fun a = Fun (Int -> a)
deriving (Functor)
-- lots of different things
data Strange a b c
= T1 a b c
| T2 [a] [b] [c] -- lists
| T3 [[a]] [[b]] [[c]] -- nested lists
| T4 (c,(b,b),(c,c)) -- tuples
| T5 ([c],Strange a b c) -- tycons
| T6 (Int -> c) -- function types
| T7 (a -> (c,a)) -- functions and tuples
| T8 ((c -> a) -> a) -- continuation
deriving (Functor)
data NotPrimitivelyRecursive a
= S1 (NotPrimitivelyRecursive (a,a))
| S2 a
deriving (Functor,Eq)
data Eq a => StupidConstraint a b = Stupid a b
deriving (Functor)
-- requires Functor constraint on f and g
data Compose f g a = Compose (f (g a))
deriving (Functor)
-- We can't derive Functor for the following type.
-- it needs both (Functor (f Int)) and (Functor (f Bool))
-- i.e.:
-- instance (Functor (f Bool), Functor (f Int)) => Functor (ComplexConstraint f)
-- This requires FlexibleContexts and UndecidableInstances
data ComplexConstraint f a = ComplexContraint (f Int (f Bool a,a))
-- deriving (Functor)
data Universal a
= Universal (forall b. (b,[a]))
| Universal2 (forall f. Functor f => (f a))
| Universal3 (forall a. a -> Int) -- reuse a
| NotReallyUniversal (forall b. a)
deriving (Functor)
-- Ghc doesn't allow deriving for non-Haskell98 data constructors
data Existential b
= forall a. ExistentialList [a]
| forall f. Functor f => ExistentialFunctor (f b)
| forall b. SneakyUseSameName (b -> Bool)
-- deriving (Functor)
-- Don't get confused by synonyms
type IntFun a = Int -> a
data IntFunD a = IntFunD (IntFun a)
deriving (Functor)
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