hashmap withdrawal and poor haskell style

[Yoann Padioleau]

Michal Wallace <sabren@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@manifestation.com 
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-- 
          Yoann  Padioleau,  INSA de Rennes, France,
Opinions expressed here are only mine. Je n'écris qu'à titre personnel.
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