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Haskell question

Haskell question

srose34	10 Oct, 2009 - 11:27 AM Post #1
New D.I.C Head Joined: 10 Oct, 2009 Posts: 4	Hi I have to write a Function which goes by the following: CODE Int -> [Char] -> [Char] The function takes the user inputted integer and takes that number of characters of the start of the list and moves them to the end of that list. The Function is meant to return an error if the number is less than 0 or greater than the list of characters. How do I implement the error? Here is what I have without the error part: CODE rotate x str = drop x str ++ take x str Please help Thanks This post has been edited by srose34: 10 Oct, 2009 - 11:52 AM
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mostyfriedman	RE: Haskell Question 11 Oct, 2009 - 10:12 AM Post #2
Striving Student Joined: 24 Oct, 2008 Posts: 3,214 Thanked: 357 times Dream Kudos: 600 Expert In: Learning My Contributions	in haskell there is an error function called error which takes a string as an argument and returns that string..so you can check if the number is less then 0 and call the function..someting like this CODE rotate x string \| x < 0 = error "the number you entered is invalid" --rest of the code here
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Raynes	RE: Haskell Question 13 Oct, 2009 - 05:21 AM Post #3
Resident Witch. No, really. Joined: 5 Jan, 2009 Posts: 957 Thanked: 14 times Dream Kudos: 250 My Contributions	mostyfriedman is right. I will note however, that the 'error' function will bail out of your program immediately. If the error is absolutely catastrophic, and there is no returning from it, the error function is a good choice. However, if you just want to throw an exception, but let the program continue, I suggest you check out the Control.Exception module: http://haskell.org/ghc/docs/latest/html/li...-Exception.html May the functions be with you.
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srose34	RE: Haskell Question 13 Oct, 2009 - 11:55 AM Post #4
New D.I.C Head Joined: 10 Oct, 2009 Posts: 4	Hi Thanks for the replies. i got it working now.
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