#6064: InstanceD declaration does not allow for explicit TyVarBndrs
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Reporter: goldfire | Owner: goldfire
Type: feature request | Status: new
Priority: normal | Component: Template Haskell
Version: 7.5 | Keywords: TemplateHaskell InstanceD
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Changes (by goldfire):
* owner: => goldfire
Comment:
I've attached a patch that does the above. This is a breaking change, so
I'm not convinced it should be made, but I would like an alternative to
using kind variables in instance declarations with TH. (The other route
would be to allow the use of undeclared kind variables in the head of an
instance declaration.)
One particular potential annoyance with this change is that all type
variables used in an instance declaration produced in TH are required to
be declared in the TyVarBndrs. It is conceivable to relax this restriction
by checking for the declarations and inferring them if they are not there,
but this idea is not implemented in the patch because it feels, well,
patchy.
I have not fully validated nor updated the test cases with respect to this
change, but would be happy to do so if the change is desired. Please let
me know if you would like this!
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6064#comment:1>
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