GHC matches -- as a varsym when lexing a qvarsym

GHC seems only to exclude the line comment marker -- when lexing a varsym and not a qvarsym.

This can be observed in the following code

module Demo where

x Demo.-- y = (x,y)

Generating this surprising error message

/Users/emertens/Desktop/Demo.hs:3:3: error:
    Qualified name in binding position: Demo.--

and excludes this definition perhaps?

example f = Just.-- comment
            f

Which might either have lexed as Just . -- comment, or it might have lexed as Just.- -, but it probably shouldn't be the case that it's a qvarsym.

At a minimum, the Haskell Report specifically excludes -- from the varsym rule, so it can't support the qvarsym rule match that it is now.

Trac metadata

Trac field	Value
Version	8.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture