Re: Pattern guards

On Sun, Oct 01, 2006 at 02:08:35AM +0200, Yitzchak Gale wrote:

An important clarification: the main monad at work here is the Exit monad. The "bind" notation in a pattern guard is just an obfuscated Exit monad. However, in many simple examples, the Maybe monad can be used as a special case of the Exit monad.

You don't use >>=, just >>. Similarly Exit is used only in the form Exit e (), which is equivalent to Maybe e, i.e. if we define exitMaybe :: Exit e () -> Maybe e exitMaybe (Continue _) = Nothing exitMaybe (Exit e) = Just e then we have runExit m = fromJust (exitMaybe m) exitMaybe (x >> y) = exitMaybe x `mplus` exitMaybe y exitMaybe (maybeExit m) = m so we can replace the Exit monad with Maybe.