Inclusion of Either within Base.

Straightforward port of Either from Idris to Idris2.
This commit is contained in:
Jan de Muijnck-Hughes 2019-07-18 16:32:19 +01:00
parent b1081e6e04
commit 5823d6b294
2 changed files with 86 additions and 2 deletions

84
libs/base/Data/Either.idr Normal file
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@ -0,0 +1,84 @@
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

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@ -6,6 +6,7 @@ modules = Control.Monad.Identity,
Control.WellFounded,
Data.Buffer,
Data.Either,
Data.Fin,
Data.IORef,
Data.List,
@ -18,11 +19,10 @@ modules = Control.Monad.Identity,
Data.Stream,
Data.Strings,
Data.Vect,
Decidable.Equality,
System,
System.Concurrency.Raw,
System.File,
System.REPL