Can't make operator called ~#
In response to:
infixl 8 ~#
parse error on input `~#'
infixl 8 ~$ infixl 8 !#
are both fine.
Hugs version September 2006 accepts ~#
GHC seems to barf over ~# in any context.
(The reason I have this version of GHC is that it comes with the Haskell Platform Ubuntu package right now.)