Reverse do notation: lexer bug?

[dons]

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?

[simonmar]

I'm not quite sure how that sneaked in, but it seems to be my fault and I've now removed it.

[dherman]

Would it be possible to revisit this decision? It's really a nice notation for interpreters (rho |- expr -> value) and type checkers that annotate their results (Gamma |- expr ::: type -> expr'). Don suggested an opt-in compiler flag or pragma. That would be fine with me.

[igloo]

Note that similar syntax is now used by the view patterns extension, which might add confusion.

[morabbin]

Bump; what's the dealio?