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List: haskell
Subject: Re: [Haskell] Re: Help : A problem with IO
From: "abdullah abdul Khadir" <abdullah.ak2002 () gmail ! com>
Date: 2008-11-27 18:22:57
Message-ID: 719881900811271010r313d3becqefa9fa4b772b5666 () mail ! gmail ! com
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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 <666wman@gmail.com> 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 <abdullah.ak2002@gmail.com>
>
>> 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 ""
>> else cs <- 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')
>> then return True
>> else return 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
>>
>>
>
[Attachment #5 (text/html)]
Thanks all,<br> \
I got it working finally. What did i learn ?<br>a) I need to put a do after else for \
more than one instruction (?)<br>b) All similar type of questions are to be \
redirected to haskell-beginner and haskell-cafe<br> \
<br>Points noted. <br>Thank \
you once again,<br>Abdullah Abdul Khadir<br><br><br><br><div class="gmail_quote">On \
Wed, Nov 26, 2008 at 10:56 PM, wman <span dir="ltr"><<a \
href="mailto:666wman@gmail.com">666wman@gmail.com</a>></span> wrote:<br> \
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); \
margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">if it should really read whole line, \
it must try to somehow chain the values into the string / list of chars (using (:) \
)<div class="Ih2E3d"> <br><br>getMyLine :: IO [Char]<br>
getMyLine = do<br>
c <- getChar<br>
if (c == '\n')<br></div>
then return "" -- imho [] looks nicer ;-)<br>
else do<br> rest <- \
getMyLine<br> return $ c : rest<br> <br>-- or<div \
class="Ih2E3d"><br><br>getMyLine :: IO [Char]<br>getMyLine = do<br> c \
<- getChar<br> if (c == '\n')<br></div> then \
return "" -- imho [] looks nicer ;-)<br> else getMyLine \
>>= return . (c:)<br> <br>
-- or even shorter and still equivalent ;-)<br><br>getMyLine :: IO \
[Char]<br>getMyLine = getChar >>= (\c -> if (c == '\n') then \
return [] else fmap (c:) getMyLine)<br><br><br><br><div class="gmail_quote">
2008/11/26 abdullah abdul Khadir <span dir="ltr"><<a \
href="mailto:abdullah.ak2002@gmail.com" \
target="_blank">abdullah.ak2002@gmail.com</a>></span><br><blockquote \
class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt \
0pt 0.8ex; padding-left: 1ex;"> <div><div></div><div class="Wj3C7c">
Hi,<br><br> The function getMyLine written by me is intended for \
getting a complete string from the standard input. <br><br>import IO \
<br><div><div></div><div><br>getMyLine :: IO [Char]<br>
getMyLine = do<br>
\
c <- getChar<br>
\
if(c == '\n')<br>
\
then return ""<br>
\
else cs <- getMyLine<br>
&n \
bsp; \
return [c]<br>
<br></div></div>However I keep getting the following error:<br><br>io.hs:14:2: Parse \
error in pattern<br>Failed, modules loaded: \
none.<br><br> 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. <br>
<br>checkd :: IO Bool<br>
checkd = do<br>
\
c <- getChar<br>
\
if(c=='d')<br>
\
then return True<br>
\
else return False<br>
<br>
Prelude> :load ./io.hs<br>[1 of 1] Compiling \
Main ( io.hs, \
interpreted )<br>Ok, modules loaded: Main.<br>*Main> checkd<br>d<br>True<br><br> \
<br></div></div><div \
class="Ih2E3d">_______________________________________________<br> Haskell mailing \
list<br> <a href="mailto:Haskell@haskell.org" \
target="_blank">Haskell@haskell.org</a><br> <a \
href="http://www.haskell.org/mailman/listinfo/haskell" \
target="_blank">http://www.haskell.org/mailman/listinfo/haskell</a><br> \
<br></div></blockquote></div><br> </blockquote></div><br>
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