On Sat, Oct 23, 2004 at 08:55:16PM +0300, Einar Karttunen wrote:
Are there any examples of using ArrowLoop outside the signal functions? Instances are declared for ordinary functions and Kleisli arrows, but how should they be actually used?
You wouldn't normally use those instances directly. With ordinary functions, you can just use recursion; with monads you can use Control.Monad.Fix.mfix (or monadic do-notation, which reduces to the same thing). Using loop for such arrows would be equivalent, but more awkward. Most of the useful examples seen so far in "proper arrows" have been in the different kinds of signal processors. Another example might be plumbing of attributes in a parsing arrow (though the loop in this case doesn't satisfy right tightening), where you want to pass values of later symbols to the parsers for earlier ones. With a monadic parser you'd do this using with mfix; with an arrow-based one, you'd use loop.