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Make fromLeft/fromRight total functions by providing default values #48

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Merged
merged 2 commits into from
Oct 15, 2020
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Make fromLeft/fromRight total functions by providing default values #48

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Make fromLeft/fromRight total functions by providing default values
JordanMartinez Feb 15, 2019
9b0a6e9
Update documentation to use hdgarrood's suggestion
JordanMartinez Feb 23, 2019
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22 changes: 13 additions & 9 deletions src/Data/Either.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -251,15 +251,19 @@ isLeft = either (const true) (const false)
isRight :: forall a b. Either a b -> Boolean
isRight = either (const false) (const true)

-- | A partial function that extracts the value from the `Left` data constructor.
-- | Passing a `Right` to `fromLeft` will throw an error at runtime.
fromLeft :: forall a b. Partial => Either a b -> a
fromLeft (Left a) = a

-- | A partial function that extracts the value from the `Right` data constructor.
-- | Passing a `Left` to `fromRight` will throw an error at runtime.
fromRight :: forall a b. Partial => Either a b -> b
fromRight (Right a) = a
-- | A function that extracts the value from the `Left` data constructor.
-- | The first argument is a default value, which will be returned in the
-- | case where a `Right` is passed to `fromLeft`.
fromLeft :: forall a b. a -> Either a b -> a
fromLeft _ (Left a) = a
fromLeft default _ = default

-- | A function that extracts the value from the `Right` data constructor.
-- | The first argument is a default value, which will be returned in the
-- | case where a `Left` is passed to `fromRight`.
fromRight :: forall a b. b -> Either a b -> b
fromRight _ (Right b) = b
fromRight default _ = default

-- | Takes a default and a `Maybe` value, if the value is a `Just`, turn it into
-- | a `Right`, if the value is a `Nothing` use the provided default as a `Left`
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