Difference between revisions of "Stupid Curry Tricks"

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>