mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-01 01:09:03 +03:00
85 lines
2.2 KiB
Idris
85 lines
2.2 KiB
Idris
module Data.Either
|
|
|
|
||| True if the argument is Left, False otherwise
|
|
public export
|
|
isLeft : Either a b -> Bool
|
|
isLeft (Left l) = True
|
|
isLeft (Right r) = False
|
|
|
|
||| True if the argument is Right, False otherwise
|
|
public export
|
|
isRight : Either a b -> Bool
|
|
isRight (Left l) = False
|
|
isRight (Right r) = True
|
|
|
|
||| Keep the payloads of all Left constructors in a list of Eithers
|
|
public export
|
|
lefts : List (Either a b) -> List a
|
|
lefts [] = []
|
|
lefts (x::xs) =
|
|
case x of
|
|
Left l => l :: lefts xs
|
|
Right r => lefts xs
|
|
|
|
||| Keep the payloads of all Right constructors in a list of Eithers
|
|
public export
|
|
rights : List (Either a b) -> List b
|
|
rights [] = []
|
|
rights (x::xs) =
|
|
case x of
|
|
Left l => rights xs
|
|
Right r => r :: rights xs
|
|
|
|
||| Split a list of Eithers into a list of the left elements and a list of the right elements
|
|
public export
|
|
partitionEithers : List (Either a b) -> (List a, List b)
|
|
partitionEithers l = (lefts l, rights l)
|
|
|
|
||| Remove a "useless" Either by collapsing the case distinction
|
|
public export
|
|
fromEither : Either a a -> a
|
|
fromEither (Left l) = l
|
|
fromEither (Right r) = r
|
|
|
|
||| Right becomes left and left becomes right
|
|
public export
|
|
mirror : Either a b -> Either b a
|
|
mirror (Left x) = Right x
|
|
mirror (Right x) = Left x
|
|
|
|
--------------------------------------------------------------------------------
|
|
-- Conversions
|
|
--------------------------------------------------------------------------------
|
|
|
|
||| Convert a Maybe to an Either by using a default value in case of Nothing
|
|
||| @ e the default value
|
|
public export
|
|
maybeToEither : (def : Lazy e) -> Maybe a -> Either e a
|
|
maybeToEither def (Just j) = Right j
|
|
maybeToEither def Nothing = Left def
|
|
|
|
||| Convert an Either to a Maybe from Right injection
|
|
public export
|
|
eitherToMaybe : Either e a -> Maybe a
|
|
eitherToMaybe (Left _) = Nothing
|
|
eitherToMaybe (Right x) = Just x
|
|
|
|
|
|
-- Injectivity of constructors
|
|
|
|
||| Left is injective
|
|
total
|
|
leftInjective : {b : Type}
|
|
-> {x : a}
|
|
-> {y : a}
|
|
-> (Left {b = b} x = Left {b = b} y) -> (x = y)
|
|
leftInjective Refl = Refl
|
|
|
|
||| Right is injective
|
|
total
|
|
rightInjective : {a : Type}
|
|
-> {x : b}
|
|
-> {y : b}
|
|
-> (Right {a = a} x = Right {a = a} y) -> (x = y)
|
|
rightInjective Refl = Refl
|