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Recurse on the right of arrows and under foralls when inferring nominal roles from kinds #3896

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Merged
hdgarrood merged 3 commits into from
Jun 4, 2020
Merged

Recurse on the right of arrows and under foralls when inferring nominal roles from kinds #3896

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60de827
Recurse on the right of arrows when inferring nominal roles from kinds
kl0tl Jun 3, 2020
483fcc2
Recurse under foralls when inferring nominal roles from kinds
kl0tl Jun 3, 2020
308b44b
Infer nominal roles from kinds arity
kl0tl Jun 3, 2020
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16 changes: 8 additions & 8 deletions src/Language/PureScript/TypeChecker/Roles.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -139,11 +139,11 @@ inferRoles env tyName
-- the absence of a role signature, provides the safest default for a type whose
-- constructors are opaque to us.
rolesFromForeignTypeKind :: SourceType -> [Role]
rolesFromForeignTypeKind
= go []
where
go acc = \case
TypeApp _ (TypeApp _ fn k1) _k2 | eqType fn tyFunction ->
go (Nominal : acc) k1
_k ->
Nominal : acc
rolesFromForeignTypeKind k = replicate (kindArity k) Nominal

kindArity :: SourceType -> Int
kindArity = go 0 where
go n (TypeApp _ (TypeApp _ fn _) k)
| fn == tyFunction = go (n + 1) k
go n (ForAll _ _ _ k _) = go n k
go n _ = n
28 changes: 28 additions & 0 deletions tests/purs/failing/CoercibleForeign2.out
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@@ -0,0 +1,28 @@
Error found:
in module Main
at tests/purs/failing/CoercibleForeign2.purs:9:20 - 9:26 (line 9, column 20 - line 9, column 26)

No type class instance was found for
 
 Prim.Coerce.Coercible (Foreign a0 b1 c2)
 (Foreign a0 b1 d3)
 

while checking that type forall (a :: Type) (b :: Type). Coercible a b => a -> b
is at least as general as type Foreign a0 b1 c2 -> Foreign a0 b1 d3
while checking that expression coerce
has type Foreign a0 b1 c2 -> Foreign a0 b1 d3
in value declaration foreignToForeign

where a0 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)
b1 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)
c2 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)
d3 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)

See https://github.com/purescript/documentation/blob/master/errors/NoInstanceFound.md for more information,
or to contribute content related to this error.

9 changes: 9 additions & 0 deletions tests/purs/failing/CoercibleForeign2.purs
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@@ -0,0 +1,9 @@
-- @shouldFailWith NoInstanceFound
module Main where

import Safe.Coerce (coerce)

foreign import data Foreign :: Type -> Type -> Type -> Type

foreignToForeign :: forall a b c d. Foreign a b c -> Foreign a b d
foreignToForeign = coerce
28 changes: 28 additions & 0 deletions tests/purs/failing/CoercibleForeign3.out
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@@ -0,0 +1,28 @@
Error found:
in module Main
at tests/purs/failing/CoercibleForeign3.purs:9:20 - 9:26 (line 9, column 20 - line 9, column 26)

No type class instance was found for
 
 Prim.Coerce.Coercible (Foreign @k0 a1 b2)
 (Foreign @k0 a1 c3)
 

while checking that type forall (a :: Type) (b :: Type). Coercible a b => a -> b
is at least as general as type Foreign @k0 a1 b2 -> Foreign @k0 a1 c3
while checking that expression coerce
has type Foreign @k0 a1 b2 -> Foreign @k0 a1 c3
in value declaration foreignToForeign

where k0 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)
a1 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)
b2 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)
c3 is a rigid type variable
bound at (line 9, column 20 - line 9, column 26)

See https://github.com/purescript/documentation/blob/master/errors/NoInstanceFound.md for more information,
or to contribute content related to this error.

9 changes: 9 additions & 0 deletions tests/purs/failing/CoercibleForeign3.purs
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@@ -0,0 +1,9 @@
-- @shouldFailWith NoInstanceFound
module Main where

import Safe.Coerce (coerce)

foreign import data Foreign :: ∀ k. k -> k -> Type

foreignToForeign :: ∀ k (a :: k) (b :: k) (c :: k). Foreign a b -> Foreign a c
foreignToForeign = coerce