[Haskell-cafe] Re: [Haskell] Re: Help : A problem with IO
you probably got it pointed out in haskell-beginners, but in case not: On Thu, Nov 27, 2008 at 7:10 PM, abdullah abdul Khadir abdullah.ak2...@gmail.com wrote: a) I need to put a do after else for more than one instruction (?) No, the do thingy is a syntactic sugar for chaining warm, fuzzy (the preffered wannabe-joke-term for the presumably scary term monads/monadic) operations. it allows you to write in classical imperative/sequential style instead of chaining operations manually (using the and = operators, which the do notation translates into anyway). lookup some monad tutorials/docs. you are right in that if there is only one operation, no transformation is needed, so the do is unnecessary. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell] Re: Help : A problem with IO
Thanks all, I got it working finally. What did i learn ? a) I need to put a do after else for more than one instruction (?) b) All similar type of questions are to be redirected to haskell-beginner and haskell-cafe Points noted. Thank you once again, Abdullah Abdul Khadir On Wed, Nov 26, 2008 at 10:56 PM, wman [EMAIL PROTECTED] wrote: if it should really read whole line, it must try to somehow chain the values into the string / list of chars (using (:) ) getMyLine :: IO [Char] getMyLine = do c - getChar if (c == '\n') then return -- imho [] looks nicer ;-) else do rest - getMyLine return $ c : rest -- or getMyLine :: IO [Char] getMyLine = do c - getChar if (c == '\n') then return -- imho [] looks nicer ;-) else getMyLine = return . (c:) -- or even shorter and still equivalent ;-) getMyLine :: IO [Char] getMyLine = getChar = (\c - if (c == '\n') then return [] else fmap (c:) getMyLine) 2008/11/26 abdullah abdul Khadir [EMAIL PROTECTED] Hi, The function getMyLine written by me is intended for getting a complete string from the standard input. import IO getMyLine :: IO [Char] getMyLine = do c - getChar if(c == '\n') then return elsecs - getMyLine return [c] However I keep getting the following error: io.hs:14:2: Parse error in pattern Failed, modules loaded: none. I fail to understand what the error is. I tried out various things such as changing the alignment and so on to no avail. The following program, however, compiled successfully though it has the same structure as the previous program. checkd :: IO Bool checkd = do c - getChar if(c=='d') thenreturn True elsereturn False Prelude :load ./io.hs [1 of 1] Compiling Main ( io.hs, interpreted ) Ok, modules loaded: Main. *Main checkd d True ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] Re: Help : A problem with IO
Hi, The function getMyLine written by me is intended for getting a complete string from the standard input. import IO getMyLine :: IO [Char] getMyLine = do c - getChar if(c == '\n') then return elsecs - getMyLine return [c] However I keep getting the following error: io.hs:14:2: Parse error in pattern Failed, modules loaded: none. I fail to understand what the error is. I tried out various things such as changing the alignment and so on to no avail. The following program, however, compiled successfully though it has the same structure as the previous program. checkd :: IO Bool checkd = do c - getChar if(c=='d') thenreturn True elsereturn False Prelude :load ./io.hs [1 of 1] Compiling Main ( io.hs, interpreted ) Ok, modules loaded: Main. *Main checkd d True ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell] Re: Help : A problem with IO
Hi Abdullah, On Wed, 2008-11-26 at 21:48 +0530, abdullah abdul Khadir wrote: Hi, The function getMyLine written by me is intended for getting a complete string from the standard input. import IO getMyLine :: IO [Char] getMyLine = do c - getChar if(c == '\n') then return elsecs - getMyLine return [c] a) you forgot a 'do' after 'else' b) your email would be answered quicker on haskell-beginners or haskell-cafe since haskell is mainly used for announcements. Axel. ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell] Re: Help : A problem with IO
On 26 nov 2008, at 17:18, abdullah abdul Khadir wrote: Hi, The function getMyLine written by me is intended for getting a complete string from the standard input. import IO getMyLine :: IO [Char] getMyLine = do c - getChar if(c == '\n') then return elsecs - getMyLine return [c] However I keep getting the following error: io.hs:14:2: Parse error in pattern Failed, modules loaded: none. I fail to understand what the error is. I tried out various things such as changing the alignment and so on to no avail. The following program, however, compiled successfully though it has the same structure as the previous program. The else should be replaced by else do. Probably you'll also want the last line to be return (c:cs). By the way, questions like these might be more appropriate on haskell- beginners or haskell-cafe. -chris checkd :: IO Bool checkd = do c - getChar if(c=='d') thenreturn True elsereturn False Prelude :load ./io.hs [1 of 1] Compiling Main ( io.hs, interpreted ) Ok, modules loaded: Main. *Main checkd d True ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
