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

Defined in Data.HList.TypeEqO

'False ~ b => TupleType x b

Defined in Data.HList.TypeEqO

TupleType (x, y) 'True

Defined in Data.HList.TypeEqO

TupleType (x, y, z) 'True

Defined in Data.HList.TypeEqO

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

All our keywords must be registered

Instances

'False ~ flag => IsKeyFN t flag

overlapping/fallback case

Defined in Data.HList.TypeEqO

IsKeyFN (Label s -> a -> b) 'True

labels that impose no restriction on the type of the (single) argument which follows

>>> let testF (_ :: Label "a") (a :: Int) () = a+1
>>> kw (hBuild testF) (Label :: Label "a") 5 ()
6

Defined in Data.HList.Keyword

r ~ (c -> b) => IsKeyFN (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.

Defined in Data.HList.Keyword

Orphan instances

hZero ~ 'HZero => ArityFwd f hZero

'False ~ b => HEq (x :: k) (y :: k) b

HEq (x :: k) (x :: k) 'True

Show (Proxy 'False)

Methods

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

show :: Proxy 'False -> String

showList :: [Proxy 'False] -> ShowS

Show (Proxy 'True)

Methods

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

show :: Proxy 'True -> String

showList :: [Proxy 'True] -> ShowS

HNat2Integral n => Show (Proxy n)

Methods

showsPrec :: Int -> Proxy n -> ShowS

show :: Proxy n -> String

showList :: [Proxy n] -> ShowS

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