#16344: GHC infers over-polymorphic kinds
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Reporter: simonpj | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 8.6.3
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by Marge Bot ):
In [changeset:"1f5cc9dc8aeeafa439d6d12c3c4565ada524b926/ghc" 1f5cc9d/ghc]:
{{{
#!CommitTicketReference repository="ghc"
revision="1f5cc9dc8aeeafa439d6d12c3c4565ada524b926"
Stop inferring over-polymorphic kinds
Before this patch GHC was trying to be too clever
(Trac #16344); it succeeded in kind-checking this
polymorphic-recursive declaration
data T ka (a::ka) b
= MkT (T Type Int Bool)
(T (Type -> Type) Maybe Bool)
As Note [No polymorphic recursion] discusses, the "solution" was
horribly fragile. So this patch deletes the key lines in
TcHsType, and a wodge of supporting stuff in the renamer.
There were two regressions, both the same: a closed type family
decl like this (T12785b) does not have a CUSK:
type family Payload (n :: Peano) (s :: HTree n x) where
Payload Z (Point a) = a
Payload (S n) (a `Branch` stru) = a
To kind-check the equations we need a dependent kind for
Payload, and we don't get that any more. Solution: make it
a CUSK by giving the result kind -- probably a good thing anyway.
The other case (T12442) was very similar: a close type family
declaration without a CUSK.
}}}
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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16344#comment:5
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