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Today's Topics:
1. Re: why is this type wrong (Roelof Wobben)
2. Re: why is this type wrong
(Sumit Sahrawat, Maths & Computing, IIT (BHU))
3. Re: why is this type wrong (Roelof Wobben)
----------------------------------------------------------------------
Message: 1
Date: Tue, 12 May 2015 14:36:58 +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] why is this type wrong
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Message: 2
Date: Tue, 12 May 2015 18:09:52 +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] why is this type wrong
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The type of (.)
(.) :: (b -> c) -> (a -> b) -> a -> c
Means that "last' [1,2,3]" should be a function, which it isn't
You can instead try,
main = (print . last') [1,2,3]
Or equivalently,
main = print . last' $ [1,2,3]
On 12 May 2015 at 18:06, Roelof Wobben <[email protected]> wrote:
> Thanks all.
>
> I have now this :
>
> -- | The main entry point.
> last' :: [a] -> Maybe a
> last' [] = Nothing
> last' [x] = Just x
> last' (_:xs) = last' xs
>
>
> main = print . last' [1,2,3]
>
> but I see this message about main :
>
>
>
>
>
>
>
> * GHC threw an exception : Couldn't match expected type ?GHC.Types.IO
> <http://GHC.Types.IO> a0? with actual type ?a1 -> GHC.Types.IO
> <http://GHC.Types.IO> ()? I work wih the fpcomplete and they demand a main
> in the code . Roelof *
>
>
> Nicolas SCHOEMAEKER schreef op 12-5-2015 om 11:45:
>
> Hi
>
> In your definition, you seem to have forgotten the case when your list is
> empty.
> [x] won't bind on [].
>
> Regards,
> Nicolas SCHOEMAEKER
>
> (*This email was composed from a mobile phone, please** excuse** any
> resulting mistakes*)
>
> Web, Cloud Computing & WebRTC developer
> Haskell Programmer
> Artificial Intelligence & Robotics enthusiast
> On May 12, 2015, at 11:40 AM, Kim-Ee Yeoh <[email protected]> wrote:
>>
>>
>> On Tue, May 12, 2015 at 1:42 PM, Roelof Wobben <[email protected]> wrote:
>>
>> -- | The main entry point.
>>> last' :: [a] -> a
>>> last' [x] = x
>>> last' (x:xs) = last xs
>>
>>
>> Notice that the last line does no recursion: it invokes the Prelude's
>> definition of last.
>>
>> -- Kim-Ee
>>
>> ------------------------------
>>
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>>
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--
Regards
Sumit Sahrawat
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Message: 3
Date: Tue, 12 May 2015 14:48:42 +0200
From: Roelof Wobben <[email protected]>
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Subject: Re: [Haskell-beginners] why is this type wrong
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