Beginners Digest, Vol 16, Issue 26
Send Beginners mailing list submissions to beginners@haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/beginners or, via email, send a message with subject or body 'help' to beginners-requ...@haskell.org You can reach the person managing the list at beginners-ow...@haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Beginners digest..." Today's Topics: 1. Re: Chessboard Module, opinions on? (i?fai) 2. Re: Chessboard Module, opinions on... (Christian Maeder) 3. Memoization (Shawn Willden) 4. Re: Memoization (Daniel Fischer) 5. Re: Chessboard Module, opinions on? (Andy Elvey) 6. Re: Chessboard Module, opinions on? (Andy Elvey) 7. list monad question (Matthias Guedemann) 8. Re: list monad question (David Virebayre) 9. Re: list monad question (Jan Jakubuv) -- Message: 1 Date: Wed, 28 Oct 2009 11:23:31 -0400 From: i?fai Subject: Re: [Haskell-beginners] Chessboard Module, opinions on? To: Darrin Thompson Cc: Beginners@haskell.org Message-ID: <10bde766-a51e-44fd-903b-bc6c9085f...@me.com> Content-Type: text/plain; charset=iso-8859-1; format=flowed; delsp=yes If I had a clock, I would consider it :P On 2009-10-28, at 11:20 AM, Darrin Thompson wrote: > On Wed, Oct 28, 2009 at 2:33 AM, iæfai wrote: >> The chess AI process is something I still have to hunt for mind >> you, but the >> part that is the most interesting is that I am going to be >> controlling a >> $50,000 robot with this in class :P. >> > > For $50k do you get a robot that can play a serious intimidating > blitz? Can it smack the clock with Class A player _authority_? :-) > > -- > Darrin -- Message: 2 Date: Wed, 28 Oct 2009 17:01:29 +0100 From: Christian Maeder Subject: [Haskell-beginners] Re: Chessboard Module, opinions on... To: i?fai Cc: Beginners@haskell.org Message-ID: <4ae86ad9.6000...@dfki.de> Content-Type: text/plain; charset=ISO-8859-1 iæfai schrieb: > Andy, feel free. I should note that I am going to update this code to > use Text.PrettyPrint.HughesPJ shortly. In addition, it will be Using a pretty printer library for this fixed format seems unnecessary to me. C. -- Message: 3 Date: Wed, 28 Oct 2009 19:45:35 -0600 From: Shawn Willden Subject: [Haskell-beginners] Memoization To: beginners@haskell.org Message-ID: <200910281945.35769.shawn-hask...@willden.org> Content-Type: text/plain; charset="us-ascii" Hi, I've just begun experimenting with Haskell, and I'm having a lot of fun, but my first semi-serious program is in need of some optimization, and based on the results of profiling I think a really good start is to memoize one particular function which is called many, many times (and currently consumes over 80% of the program run time). The function takes a two-dimensional range and a location within that range and returns a list of the locations vertically and horizontally adjacent to that location and within the bounds type Bounds = ((Int,Int),(Int,Int)) type Location = (Int,Int) adjacentCells :: Bounds -> Location -> [Location] adjacentCells bounds (col, row) = filter valid cells where valid loc = inRange bounds loc neighborLoc' = [(col-1,row),(col+1,row),(col,row-1),(col,row+1)] The ranges are fairly small -- certainly no more than 10x10, and each location has an associated list of at most 4 neighbors (edge locations have less). During a given run of the program, the bounds are fixed. So, any tips on how I can memoize this function? I have read the Memoization page on the wiki, and I understand (I think) the recursive memoization section, but it's not clear to me how to apply that approach. Section one on non-recursive memoization seems like what I want, but I don't understand the section and the links provided haven't shed any light for me. The section uses the following notation to describe how to construct a map to be used to hold the keys and values: Map ()b := b Map (Either a a') b := (Map a b, Map a' b) Map (a,a')b := Map a (Map a' b) but I'm not sure what that notation is. It's not Haskell code, I don't think. Any and all suggestions appreciated. Thanks, Shawn. -- Message: 4 Date: Thu, 29 Oct 2009 03:20:43 +0100 From: Daniel Fischer Subject: Re: [Haskell-beginners] Memoization To: beginners@haskell.org Message-ID: <200910290320.44286.daniel.is.fisc...@web.de> Content-Type: text/plain; charset="iso-8859-1" Am Donnerstag 29 Oktober 2009 02:45:35 schrieb Shawn Willden: > Hi, > > I've just begun experimenting with Haskell, and I'm having a lot of fun, > but my first semi-serious program is in need of some optimization, and > based on the results of profiling I think a really good start is to memoi
Beginners Digest, Vol 16, Issue 27
e n > xs) > -- eliminate xs > combinations n = foldr ((. (. (:)) . flip map) . (>>=)) [[]] . replicate n > -- completely pointfree > combinations = (foldr ((. (. (:)) . flip map) . (>>=)) [[]] .) . replicate thank you, looks rather strange to me but works well. regards -- __ ___ ____ Dipl. Inf. Matthias Guedemann / __\/ _\ /__\ Computer Systems in Engineering / / \ \ /_\ Otto-von-Guericke Universitaet Magdeburg / /___ _\ \//__ Tel.: 0391 / 67-19359\/ \__/\__/ __ -- Message: 8 Date: Fri, 30 Oct 2009 13:40:13 + From: Luca Ciciriello Subject: [Haskell-beginners] beginner question To: Message-ID: Content-Type: text/plain; charset="iso-8859-1" Hi all. Just a very basic question. I need to write a function str2lsts :: String -> [[String]] in order to transorm a string like: "\"1\",\"cat\",\"dog\"§\"2\",\"duck\",\"goose\"" in the list of lists: [["1","cat","dog"],["2","duck","goose"]] I've tried to mix recursion, pattern matching and list comprehension, but the obtained result was embarrassing complex (> 20 lines of awful code). I think that a more simple solution certainly exists. Thanks in advance for any idea. Luca _ Download Messenger onto your mobile for free http://clk.atdmt.com/UKM/go/174426567/direct/01/ -- next part -- An HTML attachment was scrubbed... URL: http://www.haskell.org/pipermail/beginners/attachments/20091030/4a0586e3/attachment-0001.html -- Message: 9 Date: Fri, 30 Oct 2009 15:01:29 +0100 From: Ertugrul Soeylemez Subject: [Haskell-beginners] Re: list monad question To: beginners@haskell.org Message-ID: <20091030150129.1f758...@tritium.xx> Content-Type: text/plain; charset=US-ASCII Hello Matthias, you may want to have a look at section 11 of my monads tutorial [1], which contains monadic library functions like replicateM together with examples and detailed explanations. [1] http://ertes.de/articles/monads.html#section-11 Greets, Ertugrul. Matthias Guedemann wrote: > > Hi, > > a friend of mine wanted to write function (in Perl) that creates all tuples of > length 3 of the elements of a given list, > e.g. [(0,0,0),(0,0,1),(0,0,2),...,(5,5,5)] for the list [0..5]. Trying to get > better at Haskell, I wrote a small function using the list monad for this > (tuples > replaced with lists) > > all3 ls = do > a <- ls > b <- ls > c <- ls > return [a,b,c] > > Now I want to make it capable to create all combinations of length n instead > of > fixed length 3 (that's why list instead of tuple), but I don't really see how. > As the do notation translates to > > ls >>= \a -> etc. > > I thought it should be possible to have some sort of "foldr (>>=)" over a list > of length n, but I can't figure out how to collect the variable number of > results in a list for the "return". > > Any hints for that? > > best regards > Matthias > > -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://blog.ertes.de/ -- Message: 10 Date: Fri, 30 Oct 2009 15:39:25 +0100 From: Matthias Guedemann Subject: Re: [Haskell-beginners] Re: list monad question To: beginners Message-ID: <1256912868-sup-...@pc44es141.cs.uni-magdeburg.de> Content-Type: text/plain; charset=UTF-8 Hello Ertugrul, this looks interesting. I read Brent Yorgeys Typeclassopedia and also the work you cite in your tutorial. So I am trying to learn about Applicative, Monoids, Monads etc. by using them. Your description of the library functions comes handy, as reading the source directly does not really help if you're still struggling with understanding the concepts. And on the other hand, due to the abstract nature of monads, a lot of functionality should be "hidden" in the library (just like my rewrite of replicateM) thank you very much, will read it on the weekend regards Matthias Excerpts from Ertugrul Soeylemez's message of Fr Okt 30 15:01:29 +0100 2009: > Hello Matthias, > > you may want to have a look at section 11 of my monads tutorial [1], > which contains monadic library functions like replicateM together with > examples and detailed explanations. > > [1] http://ertes.de/articles/monads.html#section-11 > > > Greets, > Ertugrul. &
Beginners Digest, Vol 16, Issue 28
like: > > "\"1\",\"cat\",\"dog\"§\"2\",\"duck\",\"goose\"" > > in the list of lists: > > [["1","cat","dog"],["2","duck","goose"]] A variety of solutions on these blog posts, and the comments: http://gimbo.org.uk/blog/2007/04/20/splitting-a-string-in-haskell/ http://julipedia.blogspot.com/2006/08/split-function-in-haskell.html Shawn. -- Message: 4 Date: Fri, 30 Oct 2009 16:34:13 +0100 From: Matthias Guedemann Subject: Re: [Haskell-beginners] list monad question To: Daniel Fischer Cc: beginners Message-ID: <1256916789-sup-...@pc44es141.cs.uni-magdeburg.de> Content-Type: text/plain; charset=UTF-8 > Yes :D The pointfree f is nicely obfuscated. But if your friend is a perl > coder, he should > be able to appreciate that. Honestly, he just wanted a "one-loop-using solution" and was not too interested in anything using Haskell :-) > The standard way to express f, however, is liftM2 (:), so > > combinations = (foldr (liftM2 (:)) [[]] .) . replicate > -- isn't that boring? true, it's almost readable At the moment trying to use pointfree is basically pointless for me, more practice is needed. regards Matthias -- __ ___ ____ Dipl. Inf. Matthias Guedemann / __\/ _\ /__\ Computer Systems in Engineering / / \ \ /_\ Otto-von-Guericke Universitaet Magdeburg / /___ _\ \//__ Tel.: 0391 / 67-19359\/ \__/\__/ __ -- Message: 5 Date: Fri, 30 Oct 2009 15:51:46 + From: Luca Ciciriello Subject: RE: [Haskell-beginners] beginner question To: , Message-ID: Content-Type: text/plain; charset="iso-8859-1" Thanks. import Text.ParserCombinators.Parsec simple = between (char '"') (char '"') (many (satisfy (/= '"'))) multiple = sepBy simple (char ',') total = sepBy multiple (char '@') str2lsts :: String -> [[String]] str2lsts str= case parse total "" str of Left err -> error (show err) Right lsts -> lsts solves my problem. As you can see I've replaced '§' with '@' and now all works fine. Luca. > From: daniel.is.fisc...@web.de > To: beginners@haskell.org > Subject: Re: [Haskell-beginners] beginner question > Date: Fri, 30 Oct 2009 15:46:33 +0100 > > Am Freitag 30 Oktober 2009 14:40:13 schrieb Luca Ciciriello: > > Hi all. > > > > Just a very basic question. > > > > > > > > I need to write a function str2lsts :: String -> [[String]] in order to > > transorm a string like: > > > > > > > > "\"1\",\"cat\",\"dog\"§\"2\",\"duck\",\"goose\"" > > > > > > > > in the list of lists: > > > > > > > > [["1","cat","dog"],["2","duck","goose"]] > > > > > > > > I've tried to mix recursion, pattern matching and list comprehension, but > > the obtained result was embarrassing complex (> 20 lines of awful code). I > > think that a more simple solution certainly exists. > > > > splitOnToken :: Eq a => a -> [a] -> [[a]] > splitOnToken t xs > = case break (== t) xs of > (hd,tl) -> hd:case tl of > (_:r@(_:_)) -> splitOnToken t r > _ -> [] > > str2lsts = map (map read . splitOnToken ',') . splitOnToken '§' > > if things weren't enclosed in quotation marks inside the string, it would be > the nicer > > map (splitOnToken ',') . splitOnToken '§' > > , provided of course, neither ',' nor '§' are valid characters for the target > strings. > > import Text.ParserCombinators.Parsec > > simple = between (char '"') (char '"') (many (staisfy (/= '"'))) > -- alternative: simple = char '"' >> manyTill anyChar (char '"') > > multiple = sepBy simple (char ',') > > total = sepBy multiple (char '§') > > str2lsts str > = case parse total "" str of > Left err -> error (show err) > Right lsts -> lsts > > > > > > > > > Thanks in advance for any idea. > > > > > > > > Luca > > > ___ &g
