Difference between revisions of "Stupid Curry Tricks"

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(Added code for frequency.hs)
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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.
 
 
<haskell>
 
--system to show character frequencies in a set of strings
 
import System.IO
 
import Data.Char(toLower)
 
 
--letters to scan for
 
letters = ['a'..'z']
 
 
--counts the ocurences of a particualr letter
 
countLetters :: Char -> [Char] -> Int
 
countLetters target str = length (filter (\c -> c == target) str)
 
 
--creates a curryed version of countletters for a particular letter
 
makeCounter :: Char -> ([Char] -> Int)
 
makeCounter c = countLetters c
 
 
--creates a countLetters funciton for each letter in the alphabet
 
counters :: [([Char] -> Int)]
 
counters = map makeCounter letters
 
 
frequencies :: [([Char] -> Int)] -> [Char] -> [Int]
 
frequencies [] _ = []
 
frequencies (f:fs) cs = (f cs) : frequencies fs cs
 
 
freqs :: [Char] -> [(Char, Int)]
 
freqs cs = zip letters (frequencies counters cs)
 
 
--make pretty output
 
prettyPrint :: (Char, Int) -> String
 
prettyPrint (c, n) = [c] ++ ":" ++ (show n) ++ "\n"
 
 
printList :: [(Char, Int)] -> String
 
printList [] = []
 
printList ((c, i):frs) = ((c:[]) ++ ": " ++ (show i) ++ "\n") ++ printList frs
 
 
--io and main program
 
main = do
 
str <- readFile "hi.txt"
 
let out = (freqs (map toLower str))
 
putStrLn $ printList out
 
 
 
</haskell>
 

Revision as of 14:18, 6 February 2021