FP Laboratory 12
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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.
For the solution look at: openFile :: FilePath -> IOMode -> IO Handle
The Handle
can used to work with a file. The function to read a content: hGetContents :: Handle -> IO String
At the end, you should close the opened file handle: hClose :: Handle -> IO ()
Alternatively you can use : readFile :: FilePath -> IO String
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