[Yhc] Yhc chokes on __ identifer

[Neil Mitchell]

Hi Russell

> I have a Haskell program that defines the value __ as
>
> __ = Prelude.error "Logical or arity value used"
>

I believe there is an option that handles underscores in some weird
and wonderful way, I'll dig into this tomorrow. The reason its going
wrong is because it can't tell if ___ is an upper or lower case
thingy, it tells by looking at the first non-_ character, which in
this case is none.

I think Haskell' makes a ruling on what this should mean, so I guess
we should follow that. Anyone know what it is offhand?

Thanks

Neil