Data.HList.TypeEqO

The HList library

(C) 2004, Oleg Kiselyov, Ralf Laemmel, Keean Schupke

Generic type equality predicate: The implementation based on overlapping instances The only place where overlapping instances are really used besides Label5

Documentation

class TupleType (t :: *) (b :: Bool) | t -> b

Instances

TupleType () True

(~) Bool False b => TupleType x b

TupleType (x, y) True

TupleType (x, y, z) True

class IsKeyFN (t :: *) (flag :: Bool) | t -> flag

All our keywords must be registered

Instances

(~) Bool False flag => IsKeyFN t flag

overlapping/fallback case

(~) * r (c -> b) => IsKeyFN (K k s c -> r) True

The purpose of this instance is to be able to use the same Symbol (type-level string) at different types. If they are supposed to be the same, then use Label instead of K

>>> let kA = K :: forall t. K "a" t
>>> let testF (K :: K "a" Int) a1 (K :: K "a" Integer) a2 () = a1-fromIntegral a2

therefore the following options works:

>>> kw (hBuild testF) kA (5 :: Int) kA (3 :: Integer) ()
2

>>> kw (hBuild testF) (K :: K "a" Integer) 3 (K :: K "a" Int) 5 ()
2

But you cannot leave off all Int or Integer annotations.

Orphan instances

(~) HNat hZero HZero => ArityFwd f hZero

(~) Bool False b => HEq k x y b

HEq k x x True

Show (Proxy Bool False)

Methods

showsPrec :: Int -> Proxy Bool False -> ShowS

show :: Proxy Bool False -> String

showList :: [Proxy Bool False] -> ShowS

Show (Proxy Bool True)

Methods

showsPrec :: Int -> Proxy Bool True -> ShowS

show :: Proxy Bool True -> String

showList :: [Proxy Bool True] -> ShowS

HNat2Integral n => Show (Proxy HNat n)

Methods

showsPrec :: Int -> Proxy HNat n -> ShowS

show :: Proxy HNat n -> String

showList :: [Proxy HNat n] -> ShowS

Arity f n => ArityFwd (x -> f) (HSucc n)