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| − | This is a useless piece of code that counts and prints the number of times each character in the English alphabet occurs in a string. This version is hard-coded to read from the file "hi.txt", but it can easily be modified to interact with standard IO or read a file passed on the command line. The most interesting part is the use of currying to generate the counting functions.
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| − | <haskell>
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| − | --system to show character frequencies in a set of strings
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| − | import System.IO
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| − | import Data.Char(toLower)
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| − |
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| − | --letters to scan for
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| − | letters = ['a'..'z']
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| − |
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| − | --counts the ocurences of a particualr letter
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| − | countLetters :: Char -> [Char] -> Int
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| − | countLetters target str = length (filter (\c -> c == target) str)
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| − |
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| − | --creates a curryed version of countletters for a particular letter
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| − | makeCounter :: Char -> ([Char] -> Int)
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| − | makeCounter c = countLetters c
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| − |
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| − | --creates a countLetters funciton for each letter in the alphabet
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| − | counters :: [([Char] -> Int)]
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| − | counters = map makeCounter letters
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| − |
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| − | frequencies :: [([Char] -> Int)] -> [Char] -> [Int]
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| − | frequencies [] _ = []
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| − | frequencies (f:fs) cs = (f cs) : frequencies fs cs
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| − |
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| − | freqs :: [Char] -> [(Char, Int)]
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| − | freqs cs = zip letters (frequencies counters cs)
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| − |
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| − | --make pretty output
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| − | prettyPrint :: (Char, Int) -> String
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| − | prettyPrint (c, n) = [c] ++ ":" ++ (show n) ++ "\n"
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| − |
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| − | printList :: [(Char, Int)] -> String
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| − | printList [] = []
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| − | printList ((c, i):frs) = ((c:[]) ++ ": " ++ (show i) ++ "\n") ++ printList frs
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| − |
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| − | --io and main program
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| − | main = do
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| − | str <- readFile "hi.txt"
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| − | let out = (freqs (map toLower str))
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| − | putStrLn $ printList out
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| − | </haskell>
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