[GHC] #9022: TH pretty printer and GHC parser semicolon placement mismatch

23 Apr 2014

      #9022: TH pretty printer and GHC parser semicolon placement mismatch
----------------------------+----------------------------------------------
       Reporter:  roldugin  |             Owner:
           Type:  bug       |            Status:  new
       Priority:  normal    |         Milestone:
      Component:  Compiler  |           Version:  7.8.2
  (Parser)                  |  Operating System:  Unknown/Multiple
       Keywords:            |   Type of failure:  GHC rejects valid program
   Architecture:            |         Test Case:
  Unknown/Multiple          |          Blocking:
     Difficulty:  Unknown   |
     Blocked By:            |
Related Tickets:            |
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 In GHC 7.8 TemplateHaskell pretty printer started inserting explicit
 braces and semicolons.

 It puts semicolons at the end of the line as opposed to the beginning of
 the next line.

 This causes GHC to fail parsing if we try to compile the pretty printed
 code.

 {{{
 $ cat Foo.hs
 module Main where

 import Language.Haskell.TH

 main = putStrLn $ pprint foo

 foo :: Dec
 foo = barD
   where
        barD = FunD ( mkName "bar" )
                    [ Clause manyArgs (NormalB barBody) [] ]

        barBody = DoE [letxStmt, retxStmt]

        letxStmt = LetS [ ValD (VarP xName) (NormalB $ LitE $ IntegerL 5)
 [] ]

        retxStmt = NoBindS $ AppE returnVarE xVarE

        xName = mkName "x"

        returnVarE = VarE $ mkName "return"

        xVarE = VarE xName

        manyArgs = map argP [0..9]

        argP n = VarP $ mkName $ "arg" ++ show n

 $ ghc-7.8.2 Foo.hs
 [1 of 1] Compiling Main             ( Foo.hs, Foo.o )
 Linking Foo ...

 $ ./Foo | tee Bar.hs
 bar arg0 arg1 arg2 arg3 arg4 arg5 arg6 arg7 arg8 arg9 = do {let x = 5;
                                                             return x}

 $ ghc Bar.hs
 [1 of 1] Compiling Main             ( Bar.hs, Bar.o )

 Bar.hs:2:61: parse error on input `return'
 }}}

 I don't know if this is a problem with TH pretty printer or if GHC is
 supposed to parse semicolons wherever they are..

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9022
GHC http://www.haskell.org/ghc/
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