[GHC] #7748: Runtime <<loop>> due to incorrect inferred type

[GHC]

#7748: Runtime <<loop>> due to incorrect inferred type
----------------------------------------+-----------------------------------
Reporter:  jbransen                     |          Owner:                         
    Type:  bug                          |         Status:  new                    
Priority:  normal                       |      Component:  Compiler (Type checker)
 Version:  7.6.2                        |       Keywords:                         
      Os:  Unknown/Multiple             |   Architecture:  Unknown/Multiple       
 Failure:  GHC accepts invalid program  |      Blockedby:                         
Blocking:                               |        Related:                         
----------------------------------------+-----------------------------------
 There is a bug in the type checker of 7.6.1 and 7.6.2, which accepts an
 incorrect type resulting in <<loop>> at runtime. Furthermore, 7.6.2 even
 automatically infers this incorrect type. Hence, the attached code has the
 following behavior:

 - No explicit type: Code works in 7.6.1, loops in 7.6.2
 - Correct explicit type: Code works fine in 7.6.1 and 7.6.2
 - Incorrect explicit type: Code loops in 7.6.1 and 7.6.2

 The incorrect type has a parameter that is too polymorphic, i.e. an "a"
 type is accepted while the function does a pattern match on the parameter
 from which it is clear that it should be a Maybe type. In 7.4.* versions
 this incorrect type is not accepted.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7748>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler