Re: [GHC] #10142: Documentation for Ix is contradictory around minimal definition

7 Mar 2015

      #10142: Documentation for Ix is contradictory around minimal definition
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        Reporter:  goldfire          |                   Owner:  hvr
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Core Libraries    |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Changes (by hvr):

 * owner:  ekmett => hvr

Comment:

 so while `range` and `inRange` have no default implementation, `index` has
 one that is recursive:

 {{{#!hs
         -- Must specify one of index, unsafeIndex

         -- 'index' is typically over-ridden in instances, with essentially
         -- the same code, but using indexError instead of
 hopelessIndexError
         -- Reason: we have 'Show' at the instances
     {-# INLINE index #-}  -- See Note [Inlining index]
     index b i | inRange b i = unsafeIndex b i
               | otherwise   = hopelessIndexError

     unsafeIndex b i = index b i
 }}}

 So the minimal pragma should specify that we minimally need

 {{{
 range && inRange && (index || unsafeIndex)
 }}}

 I'll make a patch rightaway...

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10142#comment:1
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