Re: [GHC] #7485: Tuple constraints not properly kinded

2012-12-07 Thread GHC 
#7485: Tuple constraints not properly kinded
---+
  Reporter:  goldfire  |  Owner:  
  Type:  bug   | Status:  closed  
  Priority:  normal|  Milestone:  
 Component:  Compiler  |Version:  7.7 
Resolution:  invalid   |   Keywords:  ConstraintKinds 
Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown  | Difficulty:  Unknown 
  Testcase:|  Blockedby:  
  Blocking:|Related:  
---+
Changes (by simonpj):

  * status:  new = closed
  * difficulty:  = Unknown
  * resolution:  = invalid


Comment:

 I think that is as expected. In the source language at least, `*` and
 `Constraint` are distict kinds.  So `(,)` has to have a particular kind,
 and it's `* - * - *`.  However the distfix syntax version `(a,b)` has
 special treatment so that we can use the same syntax for type tuples and
 constraint tuples.

 It's not dissimilar to `(-)`. You can write `Int# - Int`, but `(-)` as
 a separate type constructor has the more restrictive kind `(-) :: * - *
 - *`.

 I'm open to improvements.  And/or suggested documentation.

-- 
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7485#comment:1
GHC http://www.haskell.org/ghc/
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[GHC] #7485: Tuple constraints not properly kinded

2012-12-06 Thread GHC 
#7485: Tuple constraints not properly kinded
-+--
Reporter:  goldfire  |  Owner:  
Type:  bug   | Status:  new 
Priority:  normal|  Component:  Compiler
 Version:  7.7   |   Keywords:  ConstraintKinds 
  Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown  |  Blockedby:  
Blocking:|Related:  
-+--
 Consider this:

 {{{
 {-# LANGUAGE DataKinds, ConstraintKinds, KindSignatures #-}

 import GHC.Exts ( Constraint )

 type UnitType = (() :: *)
 type UnitConstraint = (() :: Constraint)

 type PairType = ((,) :: * - * - *)
 }}}

 So far, so good. But, adding the following causes an error:

 {{{
 type PairConstraint = ((,) :: Constraint - Constraint - Constraint)
 }}}

 The error is

 {{{
 The signature specified kind `Constraint
   - Constraint - Constraint',
   but `(,)' has kind `* - * - *'
 }}}

 In general, you can't use the prefix form of {{{(,)}}} in a constraint, to
 my surprise. It's not entirely clear what is the correct behavior here,
 but this all seems a little fishy as currently implemented.

 This was all tested on 7.7.20121130.

-- 
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7485
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler

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