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Reorder Inject instances to allow inj :: a -> a #44

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Merged
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Nov 30, 2018
Merged

Reorder Inject instances to allow inj :: a -> a #44

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9 changes: 5 additions & 4 deletions src/Data/Either/Inject.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,14 +9,15 @@ class Inject a b where
inj :: a -> b
prj :: b -> Maybe a

instance injectLeft :: Inject a (Either a b) where
instance injectReflexive :: Inject a a where
inj = identity
prj = Just

else instance injectLeft :: Inject a (Either a b) where
inj = Left
prj = either Just (const Nothing)

else instance injectRight :: Inject a b => Inject a (Either c b) where
inj = Right <<< inj
prj = either (const Nothing) prj

else instance injectReflexive :: Inject a a where
inj = identity
prj = Just
13 changes: 13 additions & 0 deletions test/Main.purs
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Expand Up @@ -26,6 +26,19 @@ main = do
{ actual: inj 100 :: MySum
, expected: in3 100
}
log "Test injection with the injectReflexive instance"
assertEqual
let
x = inj 100 :: MySum
in
{ actual: inj x :: MySum
, expected: x
}
log "Test that injection picks the left-most option"
assertEqual
{ actual: inj 100 :: Either3 Int Int Int
, expected: in1 100
}
log "Test projection"
assertEqual
{ actual: prj (in1 true :: MySum)
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