Safe Haskell	Safe
Language	Haskell98

Data.GADT.Compare

Synopsis

class GEq f => GCompare f where
- gcompare :: f a -> f b -> GOrdering a b
data GOrdering a b where
- GLT :: GOrdering a b
- GEQ :: GOrdering t t
- GGT :: GOrdering a b
class GEq f where
- geq :: f a -> f b -> Maybe (a :~: b)
type (:=) = (:~:)
defaultEq :: GEq f => f a -> f b -> Bool
defaultNeq :: GEq f => f a -> f b -> Bool
weakenOrdering :: GOrdering a b -> Ordering
defaultCompare :: GCompare f => f a -> f b -> Ordering
data (a :: k) :~: (b :: k) :: forall k. k -> k -> Type where
- Refl :: forall k (a :: k) (b :: k). a :~: a

Documentation

class GEq f => GCompare f where Source #

Type class for comparable GADT-like structures. When 2 things are equal, must return a witness that their parameter types are equal as well (GEQ).

Methods

gcompare :: f a -> f b -> GOrdering a b Source #

Instances

GCompare (TypeRep :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods gcompare :: TypeRep a -> TypeRep b -> GOrdering a b Source #
GCompare ((:~:) a :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods gcompare :: (a :~: a0) -> (a :~: b) -> GOrdering a0 b Source #
(GCompare a, GCompare b) => GCompare (Product a b :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods gcompare :: Product a b a0 -> Product a b b0 -> GOrdering a0 b0 Source #
(GCompare a, GCompare b) => GCompare (Sum a b :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods gcompare :: Sum a b a0 -> Sum a b b0 -> GOrdering a0 b0 Source #

data GOrdering a b where Source #

A type for the result of comparing GADT constructors; the type parameters of the GADT values being compared are included so that in the case where they are equal their parameter types can be unified.

Constructors

GLT :: GOrdering a b
GEQ :: GOrdering t t
GGT :: GOrdering a b

Instances

GRead (GOrdering a :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods greadsPrec :: Int -> GReadS (GOrdering a) Source #
GShow (GOrdering a :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods gshowsPrec :: Int -> GOrdering a a0 -> ShowS Source #
Eq (GOrdering a b) Source #
Instance details Defined in Data.GADT.Compare Methods (==) :: GOrdering a b -> GOrdering a b -> Bool # (/=) :: GOrdering a b -> GOrdering a b -> Bool #
Ord (GOrdering a b) Source #
Instance details Defined in Data.GADT.Compare Methods compare :: GOrdering a b -> GOrdering a b -> Ordering # (<) :: GOrdering a b -> GOrdering a b -> Bool # (<=) :: GOrdering a b -> GOrdering a b -> Bool # (>) :: GOrdering a b -> GOrdering a b -> Bool # (>=) :: GOrdering a b -> GOrdering a b -> Bool # max :: GOrdering a b -> GOrdering a b -> GOrdering a b # min :: GOrdering a b -> GOrdering a b -> GOrdering a b #
Show (GOrdering a b) Source #
Instance details Defined in Data.GADT.Compare Methods showsPrec :: Int -> GOrdering a b -> ShowS # show :: GOrdering a b -> String # showList :: [GOrdering a b] -> ShowS #

class GEq f where Source #

A class for type-contexts which contain enough information to (at least in some cases) decide the equality of types occurring within them.

Methods

geq :: f a -> f b -> Maybe (a :~: b) Source #

Produce a witness of type-equality, if one exists.

A handy idiom for using this would be to pattern-bind in the Maybe monad, eg.:

extract :: GEq tag => tag a -> DSum tag -> Maybe a
extract t1 (t2 :=> x) = do
    Refl <- geq t1 t2
    return x

Or in a list comprehension:

extractMany :: GEq tag => tag a -> [DSum tag] -> [a]
extractMany t1 things = [ x | (t2 :=> x) <- things, Refl <- maybeToList (geq t1 t2)]

(Making use of the DSum type from Data.Dependent.Sum in both examples)

Instances

GEq (TypeRep :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods geq :: TypeRep a -> TypeRep b -> Maybe (a :~: b) Source #
GEq ((:~:) a :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods geq :: (a :~: a0) -> (a :~: b) -> Maybe (a0 :~: b) Source #
(GEq a, GEq b) => GEq (Product a b :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods geq :: Product a b a0 -> Product a b b0 -> Maybe (a0 :~: b0) Source #
(GEq a, GEq b) => GEq (Sum a b :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods geq :: Sum a b a0 -> Sum a b b0 -> Maybe (a0 :~: b0) Source #

type (:=) = (:~:) Source #

Deprecated: use '(:~:)' from 'Data.Type,Equality'.

Backwards compatibility alias; as of GHC 7.8, this is the same as `(:~:)`.

defaultEq :: GEq f => f a -> f b -> Bool Source #

If f has a GEq instance, this function makes a suitable default implementation of '(==)'.

defaultNeq :: GEq f => f a -> f b -> Bool Source #

If f has a GEq instance, this function makes a suitable default implementation of '(/=)'.

weakenOrdering :: GOrdering a b -> Ordering Source #

TODO: Think of a better name

This operation forgets the phantom types of a GOrdering value.

defaultCompare :: GCompare f => f a -> f b -> Ordering Source #

data (a :: k) :~: (b :: k) :: forall k. k -> k -> Type where infix 4 #

Propositional equality. If a :~: b is inhabited by some terminating value, then the type a is the same as the type b. To use this equality in practice, pattern-match on the a :~: b to get out the Refl constructor; in the body of the pattern-match, the compiler knows that a ~ b.

Since: base-4.7.0.0

Constructors

Refl :: forall k (a :: k) (b :: k). a :~: a

Instances

TestEquality ((:~:) a :: k -> Type)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods testEquality :: (a :~: a0) -> (a :~: b) -> Maybe (a0 :~: b) #
GRead ((:~:) a :: k -> Type) Source #
Instance details Defined in Data.GADT.Show Methods greadsPrec :: Int -> GReadS ((:~:) a) Source #
GShow ((:~:) a :: k -> Type) Source #
Instance details Defined in Data.GADT.Show Methods gshowsPrec :: Int -> (a :~: a0) -> ShowS Source #
GCompare ((:~:) a :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods gcompare :: (a :~: a0) -> (a :~: b) -> GOrdering a0 b Source #
GEq ((:~:) a :: k -> Type) Source #
Instance details Defined in Data.GADT.Compare Methods geq :: (a :~: a0) -> (a :~: b) -> Maybe (a0 :~: b) Source #
a ~ b => Bounded (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods minBound :: a :~: b # maxBound :: a :~: b #
a ~ b => Enum (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods succ :: (a :~: b) -> a :~: b # pred :: (a :~: b) -> a :~: b # toEnum :: Int -> a :~: b # fromEnum :: (a :~: b) -> Int # enumFrom :: (a :~: b) -> [a :~: b] # enumFromThen :: (a :~: b) -> (a :~: b) -> [a :~: b] # enumFromTo :: (a :~: b) -> (a :~: b) -> [a :~: b] # enumFromThenTo :: (a :~: b) -> (a :~: b) -> (a :~: b) -> [a :~: b] #
Eq (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods (==) :: (a :~: b) -> (a :~: b) -> Bool # (/=) :: (a :~: b) -> (a :~: b) -> Bool #
Ord (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods compare :: (a :~: b) -> (a :~: b) -> Ordering # (<) :: (a :~: b) -> (a :~: b) -> Bool # (<=) :: (a :~: b) -> (a :~: b) -> Bool # (>) :: (a :~: b) -> (a :~: b) -> Bool # (>=) :: (a :~: b) -> (a :~: b) -> Bool # max :: (a :~: b) -> (a :~: b) -> a :~: b # min :: (a :~: b) -> (a :~: b) -> a :~: b #
a ~ b => Read (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods readsPrec :: Int -> ReadS (a :~: b) # readList :: ReadS [a :~: b] # readPrec :: ReadPrec (a :~: b) # readListPrec :: ReadPrec [a :~: b] #
Show (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods showsPrec :: Int -> (a :~: b) -> ShowS # show :: (a :~: b) -> String # showList :: [a :~: b] -> ShowS #