Difference between revisions of "FP Laboratory 12"
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− | <translate>For the solution look at: </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:openFile <code>openFile :: FilePath -> IOMode -> IO Handle</code>] | + | <translate><!--T:2--> For the solution look at: </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:openFile <code>openFile :: FilePath -> IOMode -> IO Handle</code>] |
− | <translate>The <code>Handle</code> can used to work with a file. The function to read a content: </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:hGetContents <code>hGetContents :: Handle -> IO String</code>] | + | <translate><!--T:3--> The <code>Handle</code> can used to work with a file. The function to read a content: </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:hGetContents <code>hGetContents :: Handle -> IO String</code>] |
− | <translate>At the end, you should close the opened file handle: </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:hClose <code>hClose :: Handle -> IO ()</code>] | + | <translate><!--T:4--> At the end, you should close the opened file handle: </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:hClose <code>hClose :: Handle -> IO ()</code>] |
− | <translate>Alternatively you can use : </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/Prelude.html#v:readFile <code>readFile :: FilePath -> IO String</code>] | + | <translate><!--T:5--> Alternatively you can use : </translate>[https://hackage.haskell.org/package/base-4.16.0.0/docs/Prelude.html#v:readFile <code>readFile :: FilePath -> IO String</code>] |
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Latest revision as of 12:47, 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
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