An interesting paper on Monads and Recursion is "Merging Monads and Folds for Functional Programming" Erik Meijer and Johan Jeuring
best regards, gustavo Peter Robinson said: > On Thursday 17 June 2004 12:39, Johannes Waldmann wrote: >> > while test body = do >> > (cond,res) <- body >> > if (test cond) then do rs <- while test body >> > return (res:rs) >> > else return [res] >> >> do you need the monad here? what monad is it? >> >> the problem could to be that the "return $ res: rs" >> can happen only after it is certain >> that "while test body" succeeds. >> so you won't even see the very first cons cell >> before the last one is evaluated. > See also > http://haskell.org/hawiki/TailRecursive > >> >> could you produce a (lazy) list of results instead? >> the garbage collector might be able to collect >> the list cells that are no longer needed >> >> possibly, a lazy state monad would help >> (if the computation of "while test body" cannot fail) >> >> > Is there a better way to implement (possibly infinite) loops in >> Haskell? > You could have a look at "Tackling the awkward squad: monadic > input/output, concurrency, exceptions, and foreign-language calls in > Haskell" (Simon Peyton Jones) > http://research.microsoft.com/users/simonpj/papers/marktoberdorf/ > where quite a few "control structures" are described. > Cheers, > Peter >> >> generally, don't program your own recursions - >> use pre-defined combinators instead. >> (I like to think of this as a "higher analogon" >> of "don't use goto - use block structures" from imperative >> programming) >> >> if you need monads, have a look at sequence, sequence_, mapM, mapM_ >> http://www.haskell.org/onlinereport/monad.html >> if you can do with lists, then use iterate, fold etc. >> http://www.haskell.org/onlinereport/list.html >> >> best regards, > _______________________________________________ > Haskell mailing list > [EMAIL PROTECTED] > http://www.haskell.org/mailman/listinfo/haskell _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
