Reverse do notation: lexer bug?

Noticed here:

http://calculist.blogspot.com/2007/07/cute-idiom-from-haskell.html

The following is accepted by GHC:

main = do
    getChar -> c
    print c

Yielding the same program as if we'd written;

main = do
    c <- getChar
    print c

The above blogger uses this to ingeniously embed:

gamma |- e -> v

in Haskell, but surely this is either a lexer bug, or an interesting syntactic feature that shouldn't be enabled by default?

Trac metadata

Trac field	Value
Version	6.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	dons@cse.unsw.edu.au
Operating system	Unknown
Architecture	Unknown