Question

I often use Python to replace various types of characters in text, using scripts that look like this:

#!/usr/bin/env python                                                                                                                                                                                                                                                         
# coding=UTF-8

import sys

for file in sys.argv[1:]:                                                                                                                                                                                                                                                     
    f = open(file)                                                                                                                                                                                                                                                            
    fs = f.read()
    r1 = fs.replace('\n',' ')
    r2 = r1.replace('\r',' ')                                                                                                                                                                                                                                                   
    r3 = r2.replace('. ','.\n\n')                                                                                                                                                                                                                                                   
    r4 = r3.replace('é','e')
    r5 = r4.replace('\xc2',' ')
    r6 = r5.replace('\xa0',' ')
    r7 = r6.replace(' ',' ')
    r8 = r7.replace(' ',' ')
    r9 = r8.replace('\n ','\n')
    f.close()                                                                                                                                                                                                                                                                 
    print r8

But I am learning Haskell now, because I am sick of Python.

My best try at doing that in Haskell is

#!/usr/bin/runhaskell 

import System.IO

main :: IO ()
main = do 
       inh <- getArgs >>= withFileLines
       outh <- -- ??
       mainloop inh outh
       hClose inh
       hClose outh

replacements :: String -> String
replacements = unwords $ map -- hmm....

…and, I have no idea where to go from there.

Answer 1

The simplest methods in Haskell involve mapping a Char -> Char replacement function (the f below) over the input, producing a new output (the interact function takes care of the fopen/fclose pattern):

main = interact $ map f
      where
        f '\n'   = ' '
        f '\r'   = ' '
        f 'é'    = 'e'
        f '\xa0' = ' '
        f c      = c

You can modify this to do your own IO, use the Text package etc, but the basic pattern of character transformations is the same.