FP Cvičení 12

From Marek Běhálek Wiki
Revision as of 10:59, 21 October 2021 by Fai0013 (talk | contribs) (Created page with "FP Cvičení 12")
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

Working with files - monad IO

  • Create a program that reads a file and number it's lines and writes it on the screen.
import System.IO
import Control.Exception

main = do fromHandle <- opf "Read from: " ReadMode
          contents <- hGetContents fromHandle
          putStr (numberLines contents)
          hClose fromHandle

opf :: String -> IOMode -> IO Handle
opf prompt mode = do putStr prompt
                     name <- getLine  
                     catch (openFile name mode )
                           (\e -> do putStr ("Can't open "++name++":"++show (e :: IOException) ++"\n")
                                     opf prompt mode)

numberLines::String -> String
numberLines text = let l = lines text
                       numbered = zip [1..] l
                       result = [show x ++".\t"++content++"\n" | (x, content)<-numbered]
                   in concat result