[GHC] #9891: Fixity declarations for pattern synonyms not persisted

16 Dec 2014

      #9891: Fixity declarations for pattern synonyms not persisted
-------------------------------------+-------------------------------------
       Reporter:  klkblake           |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:  Incorrect
     Blocked By:                     |  result at runtime
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 It appears fixity declarations for pattern synonyms only affect modules
 being compiled in the same run as the module the definition is in. For
 example, take the following files:

 Foo.hs:
 {{{#!hs
 {-# LANGUAGE PatternSynonyms #-}
 module Foo where

 data Type = Type Int RawType

 data RawType = Product Type Type
              | Num

 pattern a :*: b <- Type _ (Product a b)
 infixr 7 :*:
 }}}

 Bar.hs:
 {{{#!hs
 {-# LANGUAGE PatternSynonyms #-}
 module Main where

 import Foo

 value = Type 0 $ Product (Type 1 Num) $ Type 2 $ Product (Type 3 Num) $
 Type 4 Num

 somethingElse = 23

 main = case value of
            _ :*: _ :*: _ -> putStrLn "Success"
            _             -> putStrLn "Fail"
 }}}

 On the first compile, the executable will print "Success". Modifying Bar
 and recompiling will result in it printing "Fail". Modifying both and
 recompiling results in "Success" again.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9891
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