Type checker rejects ambiguous top level declaration.

It doesn't seem like a serious problem, but I report it anyway.

With stack's project template, I just removed main and someFunc's type signature and changed someFunc's definition to return (). stack build worked well, but stack repl emitted this error message.

D:\ghc-corePrepPgm\app\Main.hs:6:1: warning: [-Wdeferred-type-errors]
    • Couldn't match type ‘ghc-prim-0.5.0.0:GHC.Prim.Any’ with ‘IO’
      Expected type: IO ()
        Actual type: ghc-prim-0.5.0.0:GHC.Prim.Any ()
    • In the expression: main
      When checking the type of the IO action ‘main’
ghc.EXE: panic! (the 'impossible' happened)
  (GHC version 8.0.2 for x86_64-unknown-mingw32):
        corePrepPgm
  [False] cobox_r1bo = typeError
                         @ 'VoidRep
                         @ (Any :: (* -> *)) ~# (IO :: (* -> *))
                         "D:\\ghc-corePrepPgm\\app\\Main.hs:6:1: error:\n\
                         \    \\226\\128\\162 Couldn't match type \\226\\128\\152ghc-prim-0.5.0.0:GHC.Prim.Any\\226\\128\\153 with \\226\\128\\152IO\\226\\128\\153\n\
                         \      Expected type: IO ()\n\
                         \        Actual type: ghc-prim-0.5.0.0:GHC.Prim.Any ()\n\
                         \    \\226\\128\\162 In the expression: main\n\
                         \      When checking the type of the IO action \\226\\128\\152main\\226\\128\\153\n\
                         \(deferred type error)"#

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Trac metadata

Trac field	Value
Version	8.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Windows
Architecture