[GHC] #12109: Matching on pattern synonym succeeds compiled with ghc, fails with ghci

[GHC]

#12109: Matching on pattern synonym succeeds compiled with ghc, fails with ghci
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
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
 $ ghci -ignore-dot-ghci
 GHCi, version 8.0.0.20160511: http://www.haskell.org/ghc/  :? for help
 Prelude> :set -XPatternSynonyms
 Prelude> :set -XViewPatterns
 Prelude> pattern Parsed x = [(x, "")]
 Prelude> pattern Read a <- (reads -> Parsed a)
 Prelude> let Read x = "420" in (x::Int)
 420
 }}}

 works

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12109#comment:1>
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