Re: [Haskell-cafe] idea for avoiding temporaries
David Roundy [EMAIL PROTECTED] writes: I see. But how would one manage these handles? What's to keep me from accidentally copying a handle? It sounds like it'd require explicit memory management, in order to avoid ever copying a handle, if I were to implment this myself. Because you seem to write imperative code anyways: can't you simply use a specialized state monad with the array(s) hidden inside the monad as monad state? -Matthias -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] idea for avoiding temporaries
David Roundy [EMAIL PROTECTED] writes: No, the point is to avoid writing imperative code. My examples used imperative code, but that would be wrapped at the lowest level of the array library, and all the real code would be pure. Still sounds like a state monad to me. Your 'array library', I mean. -Matthias -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Shootout summary
[EMAIL PROTECTED] (Donald Bruce Stewart) writes: Fannkuch entry by Bertram Felgenhauer Mandelbrot entry I've done some benchmarking of the current entries for fannkuch and mandelbrot, and have proposed final entries for these two tests. Using = of the list monad in the current Fannkuch proposal (permutations) hides some costly ++ applications that can be also optimized away: Instead of writting permutations l = foldr perm' [l] [2..length l] where perm' n l = l = take n . iterate (rotate n) saying something like permutations l = foldr perm' [l] [2..length l] perm' n = foldr (takeIter n (rotate n)) [] takeIter :: Int - (a - a) - a - [a] - [a] takeIter 0 f x rest = rest takeIter n f x rest = x : takeIter (n-1) f (f x) rest gains us another 5% or so. -Matthias -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shortening if-then-else
Arjan van IJzendoorn [EMAIL PROTECTED] writes: Is there a shorter way to write the if-then-else part below? if (cmdType cmd) /= (CmdSitError Server) then return $ Just seat_num else return Nothing return $ if cmdType cmd /= CmdSitError Serv then Just seat_num else Nothing return $ guard (cmdType cmd /= CmdSitError Serv) return seat_num -Matthias -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shortening if-then-else
Bulat Ziganshin [EMAIL PROTECTED] writes: Hello Matthias, Tuesday, November 22, 2005, 9:17:57 PM, you wrote: MN return $ guard (cmdType cmd /= CmdSitError Serv) return seat_num return $ when (cmdType cmd /= CmdSitError Serv) (return seat_num) must also work :) Only if seat_num is of type () ... :-) -Matthias -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shortening if-then-else
Joel Reymont [EMAIL PROTECTED] writes: I don't think it will work for me either way as I'm returning m (Maybe Int) where m is my own monad. It seems that folks assumed that m itself was the maybe monad. Unless I'm mistaken the code below won't work otherwise. There are two monads involved. The outer return injects into your m monad. That's all there is for your m. Then there is the inner stuff. Because the constructor of the inner expressions, your Maybes, is an instance of MonadPlus, you can use all the nice stuff there is for MonadPlus. I'd usually write it like this ... return $ do guard (cmdType cmd /= CmdSitError Serv) return seat_num In case the guard fails, you'll get back mzero (Nothing in your case). And then there is also mplus to handle alternatives ... -Matthias On Nov 22, 2005, at 8:50 PM, Tomasz Zielonka wrote: On Tue, Nov 22, 2005 at 10:15:15PM +0300, Bulat Ziganshin wrote: return $ when (cmdType cmd /= CmdSitError Serv) (return seat_num) must also work :) But it won't. I have made this mistake too in the past ;-) -- http://wagerlabs.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] YAWQ (Yet Another Wash Question)
John Goerzen [EMAIL PROTECTED] writes: Possible, but ugly. I have about 50 lines of code that has to go in-between, so I'd be duplicating it. And, if I tried to make it into just another function, I'd have the same problem, I believe (scoping) It's all much easier: as always, you just have to use template functions for all your pages. That's all you need ... :-) Here is a recipe how I typically structure my WASH applications: - First, I write down (html) code for all the web pages and abstract over all the varying parts (input fields, submit buttons, continuation pages, etc.). As result, I get (independent) template function for all the pages. Usually, each template function lives in a separate module/file. - In the end, I write a *controller* function that both generates all the different pages by filling the holes of the templates and also ties together all the consecutive pages. And that's all you need to solve your problem as well -- just use a template function twice! Below, you'll find a small web app that toggles between two varying input pages using the scheme I described above. -Matthias module Main where import CGI main = run controller -- controller controller :: CGI () controller = let input1 = tr $ td $ textInputField empty submit1 = \ h cont - submit h cont empty page1 = stepOneTemplate input1 submit1 page2 out2= \ t - text t submit2 = \ cont - submit0 cont empty page2 = stepTwoTemplate value out2 submit2 page3 input3 = empty submit3 = \ h cont - submit F0 cont empty page3 = stepOneTemplate input3 submit3 page4 out4= \ t - text No input, sorry! submit4 = \ cont - submit0 cont empty page4 = stepTwoTemplate (const undefined) out4 submit4 page1 in page1 -- page templates stepOneTemplate inputCode submitCode nextPage = do standardQuery Input Page $ table $ do do tr $ td $ text Hello! h - inputCode tr $ td $ text Press the button! tr $ td $ submitCode h nextPage stepTwoTemplate validationCode outputCode submitCode nextPage h = do let i = validationCode h standardQuery Result Page $ table $ do tr $ td $ text Your input was ... tr $ td $ outputCode i tr $ td $ submitCode nextPage -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] YAWQ (Yet Another Wash Question)
John Goerzen [EMAIL PROTECTED] writes: On Fri, Feb 25, 2005 at 04:15:55PM +0100, Matthias Neubauer wrote: standardQuery Input Page $ table $ do do tr $ td $ text Hello! h - inputCode tr $ td $ text Press the button! tr $ td $ submitCode h nextPage I like the idea, but... doesn't this still have a problem if inputCode creates multiple fields on the screen? That is, h would only hold the last one? That's what F0, F1, F2, and friends are for. You use them to wrap multiple handles into a single object that you then pass to a submit button. E.g., my example, now with two buttons on the first step, looks as follows ... controller :: CGI () controller = let input1 = do h1 - tr $ td $ textInputField empty h2 - tr $ td $ textInputField empty return (F2 h1 h2) submit1 = \ h cont - submit h cont empty page1 = stepOneTemplate input1 submit1 page2 vali2 = \ (F2 h1 h2) - value h1 ++ and ++ value h2 out2= \ t - text t submit2 = \ cont - submit0 cont empty page2 = stepTwoTemplate vali2 out2 submit2 page3 ... The templates and all the rest stays unchanged. -Matthias -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] WASH defaults in inputFields
John Goerzen [EMAIL PROTECTED] writes: I am designing a form that will be used to edit some data that is in the database. I want users to pull up the form and have all the input fields pre-filled with the current state of the database (so they don't have to re-key all that), then the database gets updated with they hit submit. Simple to do in HTML, but I can't figure out how to do this with Wash. The inputFields don't seem to take a parameter giving a default, nor does there appear to be any way to set it later. Ideas? The first argument of input fields is used to attach additional subnodes to current xml node. I.e., if you pass additional attribute nodes as first argument, you'll be able to further specify the input field. There are predefined combinatores (like fieldSIZE or fieldVALUE) that help to construct common attribute nodes. Here is a code snippet that should clarify how to do it ... ... % iName - inputField (fieldSIZE 40 ## fieldMAXLENGTH 40 ## fieldVALUE name ## attr class name) % ... -Matthias -- Matthias Neubauer | Universität Freiburg, Institut für Informatik | tel +49 761 203 8060 Georges-Köhler-Allee 79, 79110 Freiburg i. Br., Germany | fax +49 761 203 8052 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
