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Today's Topics:
1. Re: another type problem (Alexey Shmalko)
2. Re: another type problem (Roelof Wobben)
3. Re: another type problem
(Sumit Sahrawat, Maths & Computing, IIT (BHU))
----------------------------------------------------------------------
Message: 1
Date: Tue, 12 May 2015 14:33:19 +0000
From: Alexey Shmalko <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] another type problem
Message-ID:
<CAFC2PC5SDQGj5XzCsosV5+WFf-7k=chx8vdocr8oxqxf3t1...@mail.gmail.com>
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Try fromMaybe [1]. Examples
Prelude Data.Maybe> fromMaybe [] (Just [1,2,3])
[1,2,3]
Prelude Data.Maybe> fromMaybe [1,2,3] Nothing
[1,2,3]
[1]:
https://hackage.haskell.org/package/base-4.8.0.0/docs/Data-Maybe.html#v:fromMaybe
On Tue, May 12, 2015 at 5:28 PM Roelof Wobben <[email protected]> wrote:
> Oke,
>
> And how do I do this. Haskell is a difficult one to learn,
>
> Roelof
>
>
>
> Alexey Shmalko schreef op 12-5-2015 om 16:24:
>
> Before cons'ing the result of init', you should check whether it's Just or
> Nothing. What you're doing now is something along the line with 5 : Just 3
> -- this won't typecheck.
>
> On Tue, May 12, 2015 at 5:22 PM Roelof Wobben <[email protected]> wrote:
>
>> Brandon Allbery schreef op 12-5-2015 om 16:16:
>>
>> On Tue, May 12, 2015 at 10:11 AM, Roelof Wobben <[email protected]>
>> wrote:
>>
>>> I do not understand what you are saying to me.
>>>
>>> I know that init produces a Maybe [a] . That is why I did put a Just
>>> before it.
>>>
>>
>> You are invoking it again though, and using its result as if it
>> produces [a] instead of Maybe [a].
>>
>> --
>> brandon s allbery kf8nh sine nomine
>> associates
>> [email protected]
>> [email protected]
>> unix, openafs, kerberos, infrastructure, xmonad
>> http://sinenomine.net
>>
>>
>> _______________________________________________
>> Beginners mailing
>> [email protected]http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>>
>> What is then the right way to do. I still do not understand what you
>> are trying to make clear to me.
>>
>>
>> Roelof
>>
>>
>>
>>
>> ------------------------------
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>>
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>>
>
>
> _______________________________________________
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>
>
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Message: 2
Date: Tue, 12 May 2015 16:44:35 +0200
From: Roelof Wobben <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] another type problem
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Message: 3
Date: Tue, 12 May 2015 21:01:52 +0530
From: "Sumit Sahrawat, Maths & Computing, IIT (BHU)"
<[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] another type problem
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On 12 May 2015 at 20:14, Roelof Wobben <[email protected]> wrote:
> Thanks,
>
> The right solution was this :
>
> init' (x:xs) = Just (x:fromMaybe xs (init' xs))
>
> if I understand it right x:fromMaybe xs takes care that from xs the just
> or Nothing is removed ?
>
>
Trying it out in ghci,
fromMaybe [1,2] Nothing == [1,2]
fromMaybe [1,2] Just [3] == [3]
It seems like that should indeed work.
Roelof
>
>
>
> Alexey Shmalko schreef op 12-5-2015 om 16:33:
>
> Try fromMaybe [1]. Examples
>
> Prelude Data.Maybe> fromMaybe [] (Just [1,2,3])
> [1,2,3]
> Prelude Data.Maybe> fromMaybe [1,2,3] Nothing
> [1,2,3]
>
> [1]:
> https://hackage.haskell.org/package/base-4.8.0.0/docs/Data-Maybe.html#v:fromMaybe
>
> On Tue, May 12, 2015 at 5:28 PM Roelof Wobben <[email protected]> wrote:
>
>> Oke,
>>
>> And how do I do this. Haskell is a difficult one to learn,
>>
>> Roelof
>>
>>
>>
>> Alexey Shmalko schreef op 12-5-2015 om 16:24:
>>
>> Before cons'ing the result of init', you should check whether it's Just
>> or Nothing. What you're doing now is something along the line with 5 : Just
>> 3 -- this won't typecheck.
>>
>> On Tue, May 12, 2015 at 5:22 PM Roelof Wobben <[email protected]> wrote:
>>
>>> Brandon Allbery schreef op 12-5-2015 om 16:16:
>>>
>>> On Tue, May 12, 2015 at 10:11 AM, Roelof Wobben <[email protected]>
>>> wrote:
>>>
>>>> I do not understand what you are saying to me.
>>>>
>>>> I know that init produces a Maybe [a] . That is why I did put a Just
>>>> before it.
>>>>
>>>
>>> You are invoking it again though, and using its result as if it
>>> produces [a] instead of Maybe [a].
>>>
>>> --
>>> brandon s allbery kf8nh sine nomine
>>> associates
>>> [email protected]
>>> [email protected]
>>> unix, openafs, kerberos, infrastructure, xmonad
>>> http://sinenomine.net
>>>
>>>
>>> _______________________________________________
>>> Beginners mailing
>>> [email protected]http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>
>>>
>>> What is then the right way to do. I still do not understand what you
>>> are trying to make clear to me.
>>>
>>>
>>> Roelof
>>>
>>>
>>>
>>>
>>> ------------------------------
>>> [image: Avast logo] <http://www.avast.com/>
>>>
>>> Dit e-mailbericht is gecontroleerd op virussen met Avast
>>> antivirussoftware.
>>> www.avast.com
>>>
>>> _______________________________________________
>>> Beginners mailing list
>>> [email protected]
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>
>>
>>
>> _______________________________________________
>> Beginners mailing
>> [email protected]http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>>
>>
>>
>> ------------------------------
>> [image: Avast logo] <http://www.avast.com/>
>>
>> Dit e-mailbericht is gecontroleerd op virussen met Avast
>> antivirussoftware.
>> www.avast.com
>>
>> _______________________________________________
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>>
>
>
> _______________________________________________
> Beginners mailing
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>
>
>
>
> ------------------------------
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>
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>
>
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>
--
Regards
Sumit Sahrawat
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