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Updating to match new version of source page

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Updating to match new version of source page

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== Working with files - monad IO ==
* Create a program that reads a file and number it's lines and writes it on the screen.

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<syntaxhighlight lang="Haskell">
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
</syntaxhighlight>
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 == Working with files - monad IO ==
 * Create a program that reads a file and number it's lines and writes it on the screen.
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FP Laboratory 12/en - Revision history

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