#7026: Impredicative implicit parameters
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Reporter: Ashley Yakeley | Owner:
Type: bug | Status: new
Priority: normal | Milestone: _|_
Component: Compiler (Type checker) | Version: 7.4.2
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: GHC rejects valid
program
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Changes (by simonpj):
* difficulty: => Unknown
* milestone: => _|_
Comment:
Ashley, I'm astonished this ever worked!
GHC's implementation of impredicative polymorphism needs love and
attention. I started with quite an ambitious plan, but have lowered my
sights! Now the plan is to use something along the lines of
Russo/Vytiniotis QML design. The current implementation is half way
between that and something more ambitious. Moreover, we have not even
started to think about the interaction between impredicativity and
constraint solving, which is what you are trying to do.
So think your code only ever worked by accident, and I don't see how to
make it work robustly and reliably. I hope it's not mission critical to
you. Apologies.
(I'm intrigued by what you were trying to do in the first place, though.)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7026#comment:1>
GHC <http://www.haskell.org/ghc/>
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