[GHC] #12001: RFC: Add pattern synonyms to base

[GHC]

#12001: RFC: Add pattern synonyms to base
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        Reporter:  Iceland_jack      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 {{{#!hs
 pattern II :: Int -> Int#
 pattern II i      <- (I# -> i)
   where II (I# i) = i

 pattern FF :: Float -> Float#
 pattern FF f      <- (F# -> f)
   where FF (F# f) = f
 }}}

 also if GHC allowed unlifted types in pattern synonyms, should that be a
 ticket?

 {{{
 tImB.hs:6:22-25: error: …
     • Expecting a lifted type, but ‘Int#’ is unlifted
     • In the type ‘Int#’
 tImB.hs:10:22-27: error: …
     • Expecting a lifted type, but ‘Float#’ is unlifted
     • In the type ‘Float#’
 Compilation failed.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12001#comment:1>
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