Difference between revisions of "FP Laboratory 12"

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* Create a program that reads a file and number it's lines and writes it on the screen.
 
* Create a program that reads a file and number it's lines and writes it on the screen.
 
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For the solution look at: [[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:openFile <code>openFile :: FilePath -> IOMode -> IO Handle</code>]]
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Revision as of 12:38, 6 December 2021

Working with files - monad IO

  • Create a program that reads a file and number it's lines and writes it on the screen.

For the solution look at: [openFile :: FilePath -> IOMode -> IO Handle]

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