PFP Laboratory 7 - Revision history

Beh01 at 11:58, 5 November 2024

2024-11-05T11:58:45Z

Beh01 at 11:04, 31 October 2022

2022-10-31T11:04:41Z

Beh01 at 08:11, 24 October 2022

2022-10-24T08:11:13Z

Beh01 at 11:50, 30 September 2022

2022-09-30T11:50:17Z

Beh01: /* Working with files - monad IO */

2022-09-30T11:47:56Z

Working with files - monad IO

Beh01 at 09:48, 30 September 2022

2022-09-30T09:48:41Z

Beh01: Created page with "== 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: [https..."

2022-09-30T09:44:16Z

Created page with "== Working with files - monad IO == * Create a program that reads a file and number it's lines and writes it on the screen. <div> For the solution look at: </translate>[https..."

New page

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

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>]

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>]

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>]
</div>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<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>
</div>
<div style="clear:both"></div>

← Older revision		Revision as of 11:58, 5 November 2024
Line 65:		Line 65:
	</div>		</div>
	<div style="clear:both"></div>		<div style="clear:both"></div>
		+
		+	== Monads ==
		+	* Make following types instances of the type class <code>Monad</code>.
		+	<syntaxhighlight lang="Haskell">
		+	data MyMaybe a = MyJust a \| MyNothing
		+	data MyList a = MyList [a]
		+	data MyEither a b = MyLeft a \| MyRight b
		+	</syntaxhighlight>

@@ Line 41: / Line 41: @@
 * The number of steps will be defined as program's argument.
-== Monads ==
+<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
 <syntaxhighlight lang="Haskell">
-newtype State s a = State { runState :: s -> (s, a) }
+...
 </syntaxhighlight>
-Make this type the instance of <code>Monad</code>
+</div>

← Older revision		Revision as of 11:50, 30 September 2022
Line 40:		Line 40:
	* Create a program, that computes aproximation of PI using random numbers - [https://towardsdatascience.com/estimate-pi-using-random-numbers-8b13a7e8c791 Idea].		* Create a program, that computes aproximation of PI using random numbers - [https://towardsdatascience.com/estimate-pi-using-random-numbers-8b13a7e8c791 Idea].
	* The number of steps will be defined as program's argument.		* The number of steps will be defined as program's argument.
		+
		+	== Monads ==
		+
		+	* Consider you have a type:
		+	<syntaxhighlight lang="Haskell">
		+	newtype State s a = State { runState :: s -> (s, a) }
		+	</syntaxhighlight>
		+	Make this type the instance of <code>Monad</code>

← Older revision		Revision as of 09:48, 30 September 2022
Line 36:		Line 36:
	</div>		</div>
	<div style="clear:both"></div>		<div style="clear:both"></div>
		+
		+	== Computing PI ==
		+	* Create a program, that computes aproximation of PI using random numbers - [https://towardsdatascience.com/estimate-pi-using-random-numbers-8b13a7e8c791 Idea].
		+	* The number of steps will be defined as program's argument.

@@ Line 2: / Line 2: @@
 * Create a program that reads a file and number it's lines and writes it on the screen.
 <div>
-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>]
+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>]
-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>]
+The <code>Handle</code> can used to work with a file. The function to read a content:[https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:hGetContents <code>hGetContents :: Handle -> IO String</code>]
-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>]
+At the end, you should close the opened file handle: [https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:hClose <code>hClose :: Handle -> IO ()</code>]
-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>]
+Alternatively you can use : [https://hackage.haskell.org/package/base-4.16.0.0/docs/Prelude.html#v:readFile <code>readFile :: FilePath -> IO String</code>]
 </div>