#8084: Enabling PolyKinds makes some type errors weird
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Reporter: MartijnVanSteenbergen | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 7.6.3
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: None/Unknown | Unknown/Multiple
Test Case: | Difficulty: Unknown
Blocking: | Blocked By:
| Related Tickets:
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Comment (by goldfire):
I think the desired behavior here is up for debate. When I first started
with `-XPolyKinds`, I thought the messages were strange, too. Now that I
use it a lot, I find the explicit kind parameters really helpful (except
in type-level lists!). Perhaps the principled approach would be to omit
kind applications by default but enable them with a flag like `-fshow-
explicit-kind-apps`. Seeing the kind applications also helps to teach the
programmer more of what is going on under the hood. Sometimes, it is
necessary to be thinking about the implicit kind parameters to make sense
of a program, particularly with kind-polymorphic type families. For some
examples where the type families only make sense when thinking about
explicit kind application, see the discussion for #7939.
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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8084#comment:1>
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