[GHC] #15791: typeKind confuses Type and Constraint
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Fri Oct 26 14:06:07 UTC 2018
#15791: typeKind confuses Type and Constraint
-------------------------------------+-------------------------------------
Reporter: goldfire | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 8.6.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Branch:
Wiki Page: | wip/T15791
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Comment (by goldfire):
Here are the typing rules, as I see it:
{{{
t1 : Constraint
t2 : TYPE rep -- rep is a metavariable
----------------
t1 => t2 : Type
t1 : Constraint
t2 : Constraint
---------------------
t1 => t2 : Constraint
ty : TYPE rep
`a` is not free in rep
-----------------------
forall a. ty : TYPE rep
ty : Constraint
-------------------------
forall a. ty : Constraint
}}}
The rules might be missing some side conditions for type safety, etc., but
this should be enough to get `typeKind` working.
Specifically: because the kind of `a` is `TYPE blah`, then `HasCallStack
=> a` has kind `Type`. Maybe you were thinking that `t1 => t2` has the
kind of `t2`? That wouldn't work.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15791#comment:4>
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