[GHC] #5603: Impossible case alternative

[GHC]

#5603: Impossible case alternative
---------------------------------+------------------------------------------
    Reporter:  igloo             |        Owner:              
        Type:  bug               |       Status:  new         
    Priority:  highest           |    Milestone:  7.4.1       
   Component:  Compiler          |      Version:  7.3         
    Keywords:                    |     Testcase:  T5603       
   Blockedby:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Blocking:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
---------------------------------+------------------------------------------

Comment(by daniel.is.fischer):

 Might have something to do with Safe Haskell:
 {{{
 ==================== FINAL INTERFACE ====================
 interface main:Main 70320111104
   interface hash: dde4d932dd7e5dcabe2429697bb72b53
   ABI hash: 060fb3544313b988bbb91e59b614d122
   export-list hash: b2db2ff8c639b3c46c1322f9a70b23cd
   orphan hash: 693e9af84d3dfcc71e640e005bdc5e2e
   used TH splices: False
   where
 exports:
   Main.main
 module dependencies:
 package dependencies: base ghc-prim integer-gmp
 orphans: base:GHC.Base base:GHC.Float base:Text.Read.Lex
 family instance modules: base:Data.Either base:Data.Maybe
                          ghc-prim:GHC.Generics ghc-prim:GHC.Tuple
 import safe base:GHC.Base 6997be94949bcf79c273866dbf21bd74
 import safe base:Prelude 2d51f353e8baccd6fe45deb0590d3064
 import safe ghc-prim:GHC.Types e7a4b8ccaa1476f33a832341dbabb58f
 import safe integer-gmp:GHC.Integer.GMP.Internals
 dd3c71d5d955840824090bf063c0d2f2
 import safe integer-gmp:GHC.Integer.Type 710490b06d830cde12db7b3b435cebb9
 ac754e52bd8b0218f7502181f47a21a4
 }}}
 `import safe base:GHC.Base` sure looks fishy, and 7.2.1 says
 {{{
 ==================== FINAL INTERFACE ====================
 interface main:Main 7021
   interface hash: 99423326fc6440c75738cb322290a2d7
   ABI hash: f716d21202bfc2cd2f1894b53d3d4da6
   export-list hash: 91221ade6b57b319378a1225281bb6b9
   orphan hash: 693e9af84d3dfcc71e640e005bdc5e2e
   used TH splices: False
   where
 exports:
   Main.main
 module dependencies:
 package dependencies: base ghc-prim integer-gmp
 orphans: base:GHC.Base base:GHC.Float base:GHC.Num
 family instance modules: base:Data.Either base:Data.Maybe
                          ghc-prim:GHC.Ordering ghc-prim:GHC.Tuple ghc-
 prim:GHC.Types
                          ghc-prim:GHC.Unit
 import  -/  base:GHC.Base 8faff928893671eff07da1e49d208761
 import  -/  base:Prelude 292ea38da78228a142de16a2b4594082
 import  -/  ghc-prim:GHC.Types 782ea676905837bb481c02595e678205
 import  -/  integer-gmp:GHC.Integer.GMP.Internals
 4dd5cbecca9166b46f29fdf796a8b488
 import  -/  integer-gmp:GHC.Integer.Type 1586bb2165fc529b96ade91209cd4c84
 fdf2a684a14eb4c7b2a45b9babeb8722
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5603#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler