[Haskell-beginners] Beginners Digest, Vol 89, Issue 38 How to define a simple function
MJ Williams
matthewjwilliams101 at gmail.com
Tue Nov 24 04:29:16 UTC 2015
In short, your types do not match in your calculation of the half of
the length of the list. According to GHCI
length :: [a] -> Int
(/) :: Fractional a => a -> a -> a
floor :: (Integral b, RealFrac a) => a -> b
Can you see how you might run into problems with this mixed bag of types?
The only instance where you might find type compatibility between
above types would be if you were passing a value of type `Int' to a
function that accepted values of type `Integral'. `Int', if you like,
is a subset of `Integral'
A simple solution would be to replace `/' with `div' (`div :: Integral
a => a -> a -> a'). Thus, your functionwould look something like
halve :: [a] -> [[a], [a]]
halve xs = [take longitud xs, drop longitud xs]
where
longitud = div (length xs) 2
Hope that helps, and don't hesitate to come back with more questions.
Matthew
On 23/11/2015, Francisco Gutierrez <fgutiers2002 at yahoo.com> wrote:
> Dear sirs:I am defining a function halve, that breaks a list in two halfs.
> But I always get an error. Below is my code. What am I doing
> wrong?Thanks!halve xs = [take (floor (longitud/2)), drop (floor
> (longitud/2))] where longitud = length xs
>
>
> From: "beginners-request at haskell.org" <beginners-request at haskell.org>
> To: beginners at haskell.org
> Sent: Saturday, November 21, 2015 8:21 PM
> Subject: Beginners Digest, Vol 89, Issue 38
>
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> Today's Topics:
>
> 1. Re: Warning: Tab Character (Dan Stromberg)
> 2. Re: Warning: Tab Character (Jeon-Young Kang)
> 3. Re: Warning: Tab Character (Thomas Jakway)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 21 Nov 2015 16:44:21 -0800
> From: Dan Stromberg <strombrg at gmail.com>
> To: The Haskell-Beginners Mailing List - Discussion of primarily
> beginner-level topics related to Haskell <beginners at haskell.org>
> Subject: Re: [Haskell-beginners] Warning: Tab Character
> Message-ID:
> <CAOvKW55oxCcEhtqppC0bXQZjOEEv5vcYnBTWHaj9C5vhhm7g+w at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> I believe the first version of make required tabs, but some subsequent
> versions have relaxed that requirement to make things easier.
>
> Here's an example on a Linux Mint system (the 20's are of course spaces) :
> $ od -cx < Makefile
> cmd output started 2015 Sat Nov 21 04:39:47 PM PST
> 0000000 \n g o : \n . / t \n \n
> 670a 3a6f 200a 2020 2e20 742f 0a0a
> 0000016
> above cmd output done 2015 Sat Nov 21 04:39:47 PM PST
> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>
> $ make
> cmd output started 2015 Sat Nov 21 04:39:48 PM PST
> Makefile:3: *** missing separator. Stop.
> above cmd output done 2015 Sat Nov 21 04:39:48 PM PST
> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>
> $ make --version
> cmd output started 2015 Sat Nov 21 04:39:53 PM PST
> GNU Make 3.81
> Copyright (C) 2006 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.
> There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
> PARTICULAR PURPOSE.
>
> This program built for i686-pc-linux-gnu
> above cmd output done 2015 Sat Nov 21 04:39:53 PM PST
> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>
>
> I'll add that vim's Makefile syntax highlighting puts the space-indented
> line in red, suggesting an error. Changing the spaces to a single tab
> makes the red go away.
>
> HTH
>
> On Sat, Nov 21, 2015 at 3:34 PM, Thomas Jakway <tjakway at nyu.edu> wrote:
>
>> Why would make require tabs...?
>> Admittedly it's been a long time since I've written any makefiles by hand
>> but I always use spaces instead of tabs and have never had any problems.
>>
>> On Nov 21, 2015 6:01 PM, David Moberg <kaddkaka at gmail.com> wrote:
>> >
>> > Have you found "soft tabs"? That option will make TextMate use spaces
>> instead of tab characters. Read 4.11 "Using Spaces Instead of Tabs" in
>> Dan
>> Strombergs link for instrucitons.
>> >
>> > 2015-11-21 21:36 GMT+01:00 Jeon-Young Kang <jykang22 at gmail.com>:
>> >>
>> >> I've tried to choose "instead of spaces". But there is no option of
>> mine (Textmate 2 beta).
>> >>
>> >> On Sat, Nov 21, 2015 at 3:14 PM, Dan Stromberg <strombrg at gmail.com>
>> wrote:
>> >>>
>> >>>
>> >>> Perhaps enable soft tabs?
>> >>> https://manual.macromates.com/en/working_with_text
>> >>>
>> >>> This is an issue in Python too (at least from PEP8's perspective) -
>> but note that many "make" programs require tabs instead of spaces.
>> >>>
>> >>> On Sat, Nov 21, 2015 at 11:13 AM, Jeon-Young Kang
>> >>> <jykang22 at gmail.com>
>> wrote:
>> >>>>
>> >>>> Hello everyone.
>> >>>>
>> >>>>
>> >>>> I am a newbie of Haskell, using Textmate on mac.
>> >>>>
>> >>>>
>> >>>> I got the following warning. How can I fix it?
>> >>>>
>> >>>>
>> >>>> Warning:
>> >>>>
>> >>>> Tab character
>> >>>>
>> >>>> Ok, modules loaded: Main.
>> >>>>
>> >>>>
>> >>>>
>> >>>> Sincerely,
>> >>>> Young
>> >>>>
>> >>>> _______________________________________________
>> >>>> Beginners mailing list
>> >>>> Beginners at haskell.org
>> >>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>> >>>>
>> >>>
>> >>>
>> >>>
>> >>> --
>> >>> Dan Stromberg
>> >>>
>> >>> _______________________________________________
>> >>> Beginners mailing list
>> >>> Beginners at haskell.org
>> >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>> >>>
>> >>
>> >>
>> >>
>> >> --
>> >> Department of Geography
>> >> State University of New York at Buffalo
>> >>
>> >> jykang22 at gmail.com
>> >>
>> >> Jeon-Young Kang
>> >>
>> >> _______________________________________________
>> >> Beginners mailing list
>> >> Beginners at haskell.org
>> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>> >>
>> >
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>
>
>
> --
> Dan Stromberg
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> ------------------------------
>
> Message: 2
> Date: Sat, 21 Nov 2015 20:03:08 -0500
> From: Jeon-Young Kang <jykang22 at gmail.com>
> To: The Haskell-Beginners Mailing List - Discussion of primarily
> beginner-level topics related to Haskell <beginners at haskell.org>
> Subject: Re: [Haskell-beginners] Warning: Tab Character
> Message-ID:
> <CALWtiK8DqDr292Bb=J7rEa8unXBrRTt6++HSSm82DuZjY6miTQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Thanks! I figured out.
>
> On Sat, Nov 21, 2015 at 7:44 PM, Dan Stromberg <strombrg at gmail.com> wrote:
>
>>
>> I believe the first version of make required tabs, but some subsequent
>> versions have relaxed that requirement to make things easier.
>>
>> Here's an example on a Linux Mint system (the 20's are of course spaces)
>> :
>> $ od -cx < Makefile
>> cmd output started 2015 Sat Nov 21 04:39:47 PM PST
>> 0000000 \n g o : \n . / t \n \n
>> 670a 3a6f 200a 2020 2e20 742f 0a0a
>> 0000016
>> above cmd output done 2015 Sat Nov 21 04:39:47 PM PST
>> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>>
>> $ make
>> cmd output started 2015 Sat Nov 21 04:39:48 PM PST
>> Makefile:3: *** missing separator. Stop.
>> above cmd output done 2015 Sat Nov 21 04:39:48 PM PST
>> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>>
>> $ make --version
>> cmd output started 2015 Sat Nov 21 04:39:53 PM PST
>> GNU Make 3.81
>> Copyright (C) 2006 Free Software Foundation, Inc.
>> This is free software; see the source for copying conditions.
>> There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
>> PARTICULAR PURPOSE.
>>
>> This program built for i686-pc-linux-gnu
>> above cmd output done 2015 Sat Nov 21 04:39:53 PM PST
>> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>>
>>
>> I'll add that vim's Makefile syntax highlighting puts the space-indented
>> line in red, suggesting an error. Changing the spaces to a single tab
>> makes the red go away.
>>
>> HTH
>>
>> On Sat, Nov 21, 2015 at 3:34 PM, Thomas Jakway <tjakway at nyu.edu> wrote:
>>
>>> Why would make require tabs...?
>>> Admittedly it's been a long time since I've written any makefiles by
>>> hand
>>> but I always use spaces instead of tabs and have never had any problems.
>>>
>>> On Nov 21, 2015 6:01 PM, David Moberg <kaddkaka at gmail.com> wrote:
>>> >
>>> > Have you found "soft tabs"? That option will make TextMate use spaces
>>> instead of tab characters. Read 4.11 "Using Spaces Instead of Tabs" in
>>> Dan
>>> Strombergs link for instrucitons.
>>> >
>>> > 2015-11-21 21:36 GMT+01:00 Jeon-Young Kang <jykang22 at gmail.com>:
>>> >>
>>> >> I've tried to choose "instead of spaces". But there is no option of
>>> mine (Textmate 2 beta).
>>> >>
>>> >> On Sat, Nov 21, 2015 at 3:14 PM, Dan Stromberg <strombrg at gmail.com>
>>> wrote:
>>> >>>
>>> >>>
>>> >>> Perhaps enable soft tabs?
>>> >>> https://manual.macromates.com/en/working_with_text
>>> >>>
>>> >>> This is an issue in Python too (at least from PEP8's perspective) -
>>> but note that many "make" programs require tabs instead of spaces.
>>> >>>
>>> >>> On Sat, Nov 21, 2015 at 11:13 AM, Jeon-Young Kang
>>> >>> <jykang22 at gmail.com>
>>> wrote:
>>> >>>>
>>> >>>> Hello everyone.
>>> >>>>
>>> >>>>
>>> >>>> I am a newbie of Haskell, using Textmate on mac.
>>> >>>>
>>> >>>>
>>> >>>> I got the following warning. How can I fix it?
>>> >>>>
>>> >>>>
>>> >>>> Warning:
>>> >>>>
>>> >>>> Tab character
>>> >>>>
>>> >>>> Ok, modules loaded: Main.
>>> >>>>
>>> >>>>
>>> >>>>
>>> >>>> Sincerely,
>>> >>>> Young
>>> >>>>
>>> >>>> _______________________________________________
>>> >>>> Beginners mailing list
>>> >>>> Beginners at haskell.org
>>> >>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>> >>>>
>>> >>>
>>> >>>
>>> >>>
>>> >>> --
>>> >>> Dan Stromberg
>>> >>>
>>> >>> _______________________________________________
>>> >>> Beginners mailing list
>>> >>> Beginners at haskell.org
>>> >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>> >>>
>>> >>
>>> >>
>>> >>
>>> >> --
>>> >> Department of Geography
>>> >> State University of New York at Buffalo
>>> >>
>>> >> jykang22 at gmail.com
>>> >>
>>> >> Jeon-Young Kang
>>> >>
>>> >> _______________________________________________
>>> >> Beginners mailing list
>>> >> Beginners at haskell.org
>>> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>> >>
>>> >
>>> _______________________________________________
>>> Beginners mailing list
>>> Beginners at haskell.org
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>
>>
>>
>>
>> --
>> Dan Stromberg
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>>
>
>
> --
> Department of Geography
> State University of New York at Buffalo
>
> jykang22 at gmail.com
>
> Jeon-Young Kang
> -------------- next part --------------
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> ------------------------------
>
> Message: 3
> Date: Sat, 21 Nov 2015 20:22:04 -0500
> From: Thomas Jakway <tjakway at nyu.edu>
> To: The Haskell-Beginners Mailing List - Discussion of primarily
> beginner-level topics related to Haskell <beginners at haskell.org>
> Subject: Re: [Haskell-beginners] Warning: Tab Character
> Message-ID: <66118521-5ef8-4d50-b8dc-d65a38dd9620 at email.android.com>
> Content-Type: text/plain; charset=utf-8
>
> Huh, cool. I had no idea. Thanks!
>
> On Nov 21, 2015 7:44 PM, Dan Stromberg <strombrg at gmail.com> wrote:
>>
>>
>> I believe the first version of make required tabs, but some subsequent
>> versions have relaxed that requirement to make things easier.
>>
>> Here's an example on a Linux Mint system (the 20's are of course spaces)
>> :
>> $ od -cx < Makefile
>> cmd output started 2015 Sat Nov 21 04:39:47 PM PST
>> 0000000? \n?? g?? o?? :? \n?????????????????? .?? /?? t? \n? \n
>> ?????????? 670a??? 3a6f??? 200a??? 2020??? 2e20??? 742f??? 0a0a
>> 0000016
>> above cmd output done??? 2015 Sat Nov 21 04:39:47 PM PST
>> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>>
>> $ make
>> cmd output started 2015 Sat Nov 21 04:39:48 PM PST
>> Makefile:3: *** missing separator.? Stop.
>> above cmd output done??? 2015 Sat Nov 21 04:39:48 PM PST
>> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>>
>> $ make --version
>> cmd output started 2015 Sat Nov 21 04:39:53 PM PST
>> GNU Make 3.81
>> Copyright (C) 2006? Free Software Foundation, Inc.
>> This is free software; see the source for copying conditions.
>> There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
>> PARTICULAR PURPOSE.
>>
>> This program built for i686-pc-linux-gnu
>> above cmd output done??? 2015 Sat Nov 21 04:39:53 PM PST
>> dstromberg at dell-inspiron:/var/tmp/make-tabs i686-pc-linux-gnu 25234
>>
>>
>> I'll add that vim's Makefile syntax highlighting puts the space-indented
>> line in red, suggesting an error.? Changing the spaces to a single tab
>> makes the red go away.
>>
>> HTH
>>
>> On Sat, Nov 21, 2015 at 3:34 PM, Thomas Jakway <tjakway at nyu.edu> wrote:
>>>
>>> Why would make require tabs...?
>>> Admittedly it's been a long time since I've written any makefiles by hand
>>> but I always use spaces instead of tabs and have never had any problems.
>>>
>>> On Nov 21, 2015 6:01 PM, David Moberg <kaddkaka at gmail.com> wrote:
>>> >
>>> > Have you found "soft tabs"? That option will make?TextMate use spaces
>>> > instead of tab characters. Read?4.11 "Using Spaces Instead of Tabs" in
>>> > Dan Strombergs link for instrucitons.
>>> >
>>> > 2015-11-21 21:36 GMT+01:00 Jeon-Young Kang <jykang22 at gmail.com>:
>>> >>
>>> >> I've tried to choose "instead of spaces". But there is no option of
>>> >> mine (Textmate 2 beta).
>>> >>
>>> >> On Sat, Nov 21, 2015 at 3:14 PM, Dan Stromberg <strombrg at gmail.com>
>>> >> wrote:
>>> >>>
>>> >>>
>>> >>> Perhaps enable soft tabs?
>>> >>> https://manual.macromates.com/en/working_with_text
>>> >>>
>>> >>> This is an issue in Python too (at least from PEP8's perspective) -
>>> >>> but note that many "make" programs require tabs instead of spaces.
>>> >>>
>>> >>> On Sat, Nov 21, 2015 at 11:13 AM, Jeon-Young Kang
>>> >>> <jykang22 at gmail.com> wrote:
>>> >>>>
>>> >>>> Hello everyone.
>>> >>>>
>>> >>>>
>>> >>>> I am a newbie of Haskell, using Textmate on mac.
>>> >>>>
>>> >>>>
>>> >>>> I got the following warning. How can I fix it?
>>> >>>>
>>> >>>>
>>> >>>> Warning:
>>> >>>>
>>> >>>> ? ? Tab character
>>> >>>>
>>> >>>> Ok, modules loaded: Main.
>>> >>>>
>>> >>>>
>>> >>>>
>>> >>>> Sincerely,
>>> >>>> Young
>>> >>>>
>>> >>>> _______________________________________________
>>> >>>> Beginners mailing list
>>> >>>> Beginners at haskell.org
>>> >>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>> >>>>
>>> >>>
>>> >>>
>>> >>>
>>> >>> --
>>> >>> Dan Stromberg
>>> >>>
>>> >>> _______________________________________________
>>> >>> Beginners mailing list
>>> >>> Beginners at haskell.org
>>> >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>> >>>
>>> >>
>>> >>
>>> >>
>>> >> --
>>> >> Department of Geography
>>> >> State University of New York at Buffalo
>>> >>
>>> >> jykang22 at gmail.com
>>> >> ?
>>> >> Jeon-Young Kang
>>> >>
>>> >> _______________________________________________
>>> >> Beginners mailing list
>>> >> Beginners at haskell.org
>>> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>> >>
>>> >
>>> _______________________________________________
>>> Beginners mailing list
>>> Beginners at haskell.org
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>>
>>
>>
>> --
>> Dan Stromberg
>
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>
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> ------------------------------
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> End of Beginners Digest, Vol 89, Issue 38
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