Re: [Haskell-beginners] [IO String] to IO [String]

The untilexit definition is pretty straightforward. You can see that the the function operates on a string. There are two cases where nothing is returned: "" and "exit" ++ rest. In order to display a prompt before each input you will need to actually display a prompt /after/ each line, and an additional prompt before you start processing input. On Mon, Apr 1, 2013 at 4:15 PM, Ovidiu D wrote:

Thanks.

I can see it working but I don't undestand why does untilexit actually stop the processing. Can you explain that?

Also how could I display a prompt before reading each line?

On Mon, Apr 1, 2013 at 7:14 AM, Lyndon Maydwell wrote:

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Interact should be able to handle line-by-line interaction as per this example, it should even be able to handle the exit case thanks to laziness:

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main :: IO () main = interact (unlines . map reverse . lines . untilexit)

untilexit :: String -> String untilexit ('e':'x':'i':'t':_) = [] untilexit (c:t) = c : untilexit t untilexit [] = []

There will be a lot of things that it won't be able to do however.

On Mon, Apr 1, 2013 at 5:49 AM, Ovidiu D wrote:

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My problem with interact was that it doesn't give me the line when the user hits enter but instead it gives me all the lines at once when stdin is closed (unless I did something wrong)

The other problem is that I want to stop the command processing when the user types the command "exit" and it seems interact can't do that.

On Sun, Mar 31, 2013 at 2:52 PM, Lyndon Maydwell wrote:

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Depending on what you're doing with the lines, it may be worth checking out the `interact` function as well :-)

On Sun, Mar 31, 2013 at 7:42 PM, Kim-Ee Yeoh wrote:

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I would like to make this function to have the signature f : IO [String] ...such that I can get rid of the IO monad and pass the pure string

On Sun, Mar 31, 2013 at 5:19 PM, Ovidiu D wrote: list to

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the processing function.

You could use:

getContents >>= lines :: IO [String]

-- Kim-Ee

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