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Re: hashmap withdrawal and poor haskell style
by Yoann Padioleau 03 Apr '02

03 Apr '02

Remi Turk <remi(a)abcweb.nl> writes: > > -------------------- > module Main where > > import Char > import FiniteMap > > printCount :: (Char, Integer) -> IO () > printCount (letter, count) > =3D putStrLn $ letter : replicate count '*' > > countLetters :: String -> [(Char, Integer)] > countLetters letters > =3D fmToList $ addListToFM_C (+) emptyFM $ zip letters (repeat 1) > > main =3D getContents >>=3D mapM_ printCount . countLetters . filter isAl= > pha this is not exactly the same semantic than the python version, for example if 'z' is not in the contents, then you will not display 'z' (without star) and you will not respect also the order of the letter (i think) > -------------------- > > Happy Hacking > > Remi > > --=20 > See the light and feel my warm desire, > Run through your veins like the evening sun > It will live but no eyes will see it, > I'll bless your name before I die. > > Key fingerprint =3D CC90 A1BA CF6D 891C 5B88 C543 6C5F C469 8F20 70F4 > > --wRRV7LY7NUeQGEoC > Content-Type: application/pgp-signature > Content-Disposition: inline > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.0.6 (GNU/Linux) > Comment: For info see http://www.gnupg.org > > iD8DBQE8qzpFbF/EaY8gcPQRAm8DAJ44i0avXmnavtDu+OOy1mdrBL88HwCfWsx+ > GFJUUd1zm1wV8CwfqU2TN0k= > =X3DP > -----END PGP SIGNATURE----- > > --wRRV7LY7NUeQGEoC-- > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

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03 Apr '02

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Re: hashmap withdrawal and poor haskell style
by Yoann Padioleau 03 Apr '02

03 Apr '02

Michal Wallace <sabren(a)manifestation.com> writes: > module Main where > alphabet = "abcdefghijklmnopqrstuvwxyz" in haskell you can do alphabet = ['a'..'z'] > count ch str = length [c | c <- str , c == ch] can do count c s = length (filter (c ==) s) or more cryptic: count c = length . (filter (c==)) > hist str = [count letter str | letter <- alphabet] > oneline ch str = [ch] ++ " " ++ stars (count ch str) > stars x = if x == 0 > then "" > else "*" ++ stars ( x - 1 ) stars n = replicate n '*' > report str ch = do putStrLn ( oneline ch str ) > loop f (h:t) = if t == [] > then f h > else do f h > loop f t you can use mapM_ main = do content <- getContents mapM_ (\a -> report content a) alphabet > main = do content <- getContents > let rpt letter = report content letter > loop rpt alphabet > """ you dont choose the more efficient strategy cos you parse 26 times the contents of the file, it is better to do (as you did in python) parse 1 and remember the number of occurence. > > Other than ignoring upper case letters, and being really > really slow, it seems to work fine in hugs.... > > One thing I really missed was a hash / dictionary. I > tried for about an hour to use Assoc following the > examples from PLEAC: > > http://pleac.sourceforge.net/pleac_haskell/hashes.html > > > ... But I never got it working: that's because i dont really use standard haskell library, i redefine a library in a file named Common.hs where there is a constructor AssocDefault. So if you want use AssocDefault, they you have to do: module Main where import Prelude hiding (($),(^),(.),(!!),map,take,lookup,.... AS in the example in the pleac section* import Common Put your code here. so it becomes: #!/usr/bin/runhugs -98 module Main where import Prelude hiding (($),(^),(.),(!!),map,take,lookup,drop,splitAt,reverse,filter,takeWhile,dropWhile,null,foldl,length) import Common main = do s <- getContents s.downcase .foldl(\h c -> if isAlpha c then h.update c (+1) else h) (empty::AssocDefault Char Int) .(\h -> ['a'..'z'].each (\c -> putStrLn (c^replicate (h!c) '*'))) or in more standard haskell, i will do: #!/usr/bin/runhugs -98 module Main where import Prelude hiding ((.)) (.) o f = f o update k f xs = xs.map (\ (k2,v) -> if k == k2 then (k,f v) else (k2,v)) each:: (e -> IO ()) -> [e] -> IO () each = mapM_ main :: IO () main = do s <- getContents s.map toLower .foldl(\h c -> if isAlpha c then h.update c (+1) else h) [(c, 0::Int) | c <- ['a'..'z']] .each (\ (c,n) -> putStrLn (show c ++ (replicate n '*' ))) > > > :> module Main where > :> import Assoc (empty) > :> main :: IO() > :> main = do line <- getContents > :> let w = length line > :> count:: AssocDefault String Int > :> count = w.foldl (\a s -> a.update s (+1)) empty > :> print x > > -> ERROR "alphahist.hs":6 - Undefined type constructor "AssocDefault" that's because AssocDefault is a constructor that standard haskell does not define. > > Also, I'd really like to here anyone's thoughts on the code > I have above, especially concercing what I could have done > better. :) > > Thanks! > > Cheers, > > - Michal http://www.sabren.net/ sabren(a)manifestation.com > ------------------------------------------------------------ > Give your ideas the perfect home: http://www.cornerhost.com/ > cvs - weblogs - php - linux shell - perl/python/cgi - java > ------------------------------------------------------------ > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

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Re: Ex 9.9 in Paul Hudak's book
by Lennart Augustsson 03 Apr '02

03 Apr '02

> What I would like to know is how the 'fix' function could be used > to find the fixed point of a function like ( \n -> 2*n ). The 'fix' function does compute a (the least) fixed point of ( \n -> 2*n ). The least fixed point is bottom. -- Lennart

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Re: sort inefficiency
by Dylan Thurston 03 Apr '02

03 Apr '02

On Wed, Apr 03, 2002 at 09:35:51AM +0400, Serge D. Mechveliani wrote: > The Standard library specifies only the map related to the name > `sort'. This map can be described, for example, via sort-by-insertion > program. > And the algorithm choice is a matter of each particular > implementation. Implementation has right to change the algorithm. Reading this, it occurred to me that if you're very picky the implementation probably isn't allowed to pick the algorithm: you need to assume that '<' is actually a total order to have much leeway at all. (Suppose, e.g., that comparing two particular elements yields an exception.) It seems to me this is a problem with providing code as specification: you probably fix the details more than you want. Best, Dylan Thurston

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guards
by Cagdas Ozgenc 29 Mar '02

29 Mar '02

Greetings. Is it requried that the type used in guards always Bool? It seems to me that the Haskell language is dependent to Bool type, and Bool type is depending to the Haskell language causing a circular dependency problem. Of course this is not a practical issue. Is there a theoretical explanation? Thanks for taking time.

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Re: Little problem
by Jorge Adriano 27 Mar '02

27 Mar '02

[moving to haskell-cafe] > Hello > I have little problem. I want to solve this equation > > f(n-1) = f(n)+n > f(6)=6 This is a simple recursive definition.. By the way, are you sure you didn't meant: f(n-1)=f(n)+(n-1) > => f(2)=? Not exactly sure what you're after here. You could simply do: f(2) =f(3)+3 =f(4)+4+3 =f(5)+5+4+3 =f(6)+6+5+4+3 =6+6+5+4+3 =24 anyway it's simple to see, or even prove by induction, that f(n) = (\sum_{i=n+1}^{7} i) -1 = (n+8)(7-n)/2 - 1 If I'm rigth and you're formula is suposed to be f(n-1) = f(n)+n it is even easier. J.A.

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Re: Is there a name for this structure?
by dominic.j.steinitz＠britishairways.com 27 Mar '02

27 Mar '02

The name escapes me but any category theory book should supply the answer. Dominic. Tom Pledger <Tom.Pledger(a)peace.com>@haskell.org on 27/03/2002 04:22:29 Sent by: haskell-cafe-admin(a)haskell.org To: haskell-cafe cc: bcc: Subject: Is there a name for this structure? Joe English writes: : | Suppose you have two morphisms f : A -> B and g : B -> A | such that neither (f . g) nor (g . f) is the identity, | but satisfying (f . g . f) = f. Is there a conventional name | for this? Is it equivalent to saying that (f . g) is the identity on the range of f? That's shorter, though still not a snappy single word term. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------------------------------------------------------------------------- Save time by using an eTicket and our Self-Service Check-in Kiosks. For more information go to http://www.britishairways.com/eservice1

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Is there a name for this structure?
by Joe English 27 Mar '02

27 Mar '02

Not really a Haskell question, but someone here might know the answer... Suppose you have two morphisms f : A -> B and g : B -> A such that neither (f . g) nor (g . f) is the identity, but satisfying (f . g . f) = f. Is there a conventional name for this? Alternately, same question, but f and g are functors and A and B categories. In some cases (g . f . g) is also equal to g; is there a name for this as well? I find myself running into pairs of functions with this property over and over again, and am looking for a short way to describe the property... Thanks, --Joe English jenglish(a)flightlab.com

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Re: I need some help
by Jorge Adriano 26 Mar '02

26 Mar '02

> > However the user of the program give some argument then program is > > starting. And I want to use this arguments for example at the end of the > > program. What will I do. > > Good question. I've had a bad time with this, some in this list proably got > tired of me saying the same thing over and over again... those of you might > want to skip the rest of my mail :-) huh? what is this line doing here.. I thought I had cut/pasted it below, but instead I copy/pasted it (then changed it). Most of the is pretty readble, I just complain about stuff in the last part of the e-mail :-) J.A.

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