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Allow functor derivation under quantification #3295

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Merged
LiamGoodacre merged 2 commits into from
Apr 10, 2018
Merged

Allow functor derivation under quantification #3295

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46b8cf6
Allow functor derivation under quantification
i-help-tom Mar 29, 2018
a712440
Allow for constraints in derived functors, quantification shadowing
i-help-tom Mar 29, 2018
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9 changes: 8 additions & 1 deletion examples/passing/DerivingFunctor.purs
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Expand Up @@ -15,9 +15,11 @@ data M f a
| M4 (MyRecord a)

derive instance eqM :: (Eq1 f, Eq a) => Eq (M f a)

derive instance functorM :: Functor f => Functor (M f)

data T a = T (forall t. Show t => t -> a)
derive instance functorT :: Functor T

type MA = M Array

main = do
Expand All @@ -26,4 +28,9 @@ main = do
assert $ map show (M2 [0, 1] :: MA Int) == M2 ["0", "1"]
assert $ map show (M3 {foo: 0, bar: 1, baz: [2, 3]} :: MA Int) == M3 {foo: 0, bar: "1", baz: ["2", "3"]}
assert $ map show (M4 { myField: 42 }) == M4 { myField: "42" } :: MA String

case map show (T \_ -> 42) of
T f -> assert $ f "hello" == "42"
_ -> assert false

log "Done"
6 changes: 6 additions & 0 deletions src/Language/PureScript/Sugar/TypeClasses/Deriving.hs
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Expand Up @@ -742,6 +742,12 @@ deriveFunctor ss mn syns ds tyConNm = do
mkAssignment ((Label l), x) = (l, App x (Accessor l argVar))
return (lam ss arg (ObjectUpdate argVar (mkAssignment <$> updates)))

-- quantifiers
goType (ForAll scopedVar t _) | scopedVar /= iTyName = goType t

-- constraints
goType (ConstrainedType _ t) = goType t

-- under a `* -> *`, just assume functor for now
goType (TypeApp _ t) = fmap (App mapVar) <$> goType t

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