[ ghc-Bugs-753780 ] (->) used prefix doesn't work with unboxed kinds

Bugs item #753780, was opened at 2003-06-13 07:24
Message generated for change (Settings changed) made by simonpj
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Category: Compiler (Type checker)
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Simon Peyton Jones (simonpj)
Assigned to: Nobody/Anonymous (nobody)
Summary: (->) used prefix doesn't work with unboxed kinds

Initial Comment:
This fails, but should succeed
    f :: (->) Int# Int#
    f x = x


-- Here's the comment from TypeRep:
--
-- funTyCon = mkFunTyCon funTyConName 
--              (mkArrowKinds [liftedTypeKind, 
liftedTypeKind]
--                              liftedTypeKind)
-- You might think that (->) should have type (? -> ? -> 
*), and you'd be right
-- But if we do that we get kind errors when saying
--      instance Control.Arrow (->)
-- becuase the expected kind is (*->*->*).  The trouble 
is that the
-- expected/actual stuff in the unifier does not go 
contra-variant, whereas
-- the kind sub-typing does.  Sigh.  It really only 
matters if you use (->) in
-- a prefix way, thus:  (->) Int# Int#.  And this is 
unusual.


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>Comment By: Simon Peyton Jones (simonpj)
Date: 2003-12-31 16:58

Message:
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Fixed at last.

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