Modulerelude-1.2.0.0Haskell2010

Relude.Extra.Type

SPDX-License-Identifier : MIT Maintainer : Kowainik xrom.xkov@gmail.com Stability : Stable Portability : Portable

Contains useful utilities to work with Types.

1 value

Packagerelude-1.2.0.0
Exports6
LanguageHaskell2010
LicenceMIT
SourceType.hs

valuetypeName :: Typeable a => Text

Gets a string representation of a type.

NOTE: This must be used with TypeApplications language extension.

Example4 expressions

>>> typeName @()"()">>> typeName @Int"Int">>> typeName @String"[Char]">>> typeName @(Maybe Int)"Maybe Int"

familytype family (++) (xs :: [k]) (ys :: [k]) :: [k] where

Concatenates type-level lists.

Example1 expression

>>> :kind! '[ 'Just 5, 'Nothing] ++ '[ 'Just 3, 'Nothing, 'Just 1]'[ 'Just 5, 'Nothing] ++ '[ 'Just 3, 'Nothing, 'Just 1] :: [Maybe                                                              Natural]= '[ 'Just 5, 'Nothing, 'Just 3, 'Nothing, 'Just 1]

Example1 expression

>>> :kind! '[] ++ '[ 'Just 3, 'Nothing, 'Just 1]'[] ++ '[ 'Just 3, 'Nothing, 'Just 1] :: [Maybe Natural]= '[ 'Just 3, 'Nothing, 'Just 1]

# 85 "srcReludeExtra/Type.hs"

Equations

(++) '[] ys = ys
(++) (x ': xs) ys = x ': xs ++ ys

familytype family AllHave (f :: k -> Constraint) (xs :: [k]) :: Constraint where

Builds combined Constraint by applying Constraint constructor to all elements of type-level list.

Example1 expression

>>> :kind! AllHave Show '[Int, Text, Double]AllHave Show '[Int, Text, Double] :: Constraint= (Show Int, (Show Text, (Show Double, () :: Constraint)))

which is equivalent to:

(Show Int, Show Text, Show Double) :: Constraint

Equations

AllHave _1 '[] = ()
AllHave f (x ': xs) = (f x, AllHave f xs)

familytype family Elem (e :: t) (es :: [t]) :: Bool where

Check that a type is an element of a list:

Example1 expression

>>> :kind! Elem String '[]Elem String '[] :: Bool= 'False

Example1 expression

>>> :kind! Elem String '[Int, String]Elem String '[Int, String] :: Bool= 'True

Example1 expression

>>> :kind! Elem String '[Int, Bool]Elem String '[Int, Bool] :: Bool= 'False

Equations

Elem _1 '[] = 'False
Elem x (x ': xs) = 'True
Elem x (_1 ': xs) = Elem x xs

familytype family Fst (t :: k) :: k' where

Returns first element of tuple type (with kind *) or type-level tuple (with kind (k1, k2), marked by prefix quote).

Example1 expression

>>> :kind! Maybe (Fst '(Int, Text))Maybe (Fst '(Int, Text)) :: *= Maybe Int

Example1 expression

>>> :kind! Maybe (Fst (Int, Text))Maybe (Fst (Int, Text)) :: *= Maybe Int

Equations

Fst '(x, _1) = x
Fst (x, _1) = x

familytype family Snd (t :: k) :: k' where

Returns second element of tuple type (with kind *) or type-level tuple (with kind (k1, k2), marked by prefix quote).

Example2 expressions

>>> :kind! Maybe (Snd '(Int, Text))Maybe (Snd '(Int, Text)) :: *= Maybe Text>>> :kind! Maybe (Snd (Int, Text))Maybe (Snd (Int, Text)) :: *= Maybe Text

Equations

Snd '(_1, y) = y
Snd (_1, y) = y