[Haskell-beginners] Re: Beginners Digest, Vol 27, Issue 57

[Martin Tomko]

Ahaaa, the heureka moment. Stupid me, I should have tried :t null
Thanks Brent!


On 9/27/2010 6:00 PM, beginners-request at haskell.org wrote:
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>     1. Re:  matching the output of a standard function	to my
>        function definition (non-exhaustive pattern problem) (Brent Yorgey)
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> Message: 1
> Date: Mon, 27 Sep 2010 12:21:08 -0400
> From: Brent Yorgey<byorgey at seas.upenn.edu>
> Subject: Re: [Haskell-beginners] matching the output of a standard
> 	function	to my function definition (non-exhaustive pattern problem)
> To: beginners at haskell.org
> Message-ID:<20100927162108.GA5408 at seas.upenn.edu>
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> On Mon, Sep 27, 2010 at 06:15:22PM +0200, Martin Tomko wrote:
>    
>> Dear Daniel
>> that worked perfectly, thanks for the suggestion!
>>
>> One more question: how do you use null to check for empty lists?
>> something like [] == null did not work ... just chekcing, I got my
>> orignal code to work, thanks again!
>> Martin
>>      
> When in doubt, consult the types!
>
>    null :: [a] ->  Bool
>
> That is, null is a function for testing lists to see whether they are
> empty.  So rather than 'list == null' you write 'null list'.
>
> -Brent
>
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> End of Beginners Digest, Vol 27, Issue 57
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-- 
Martin Tomko
Postdoctoral Research Assistant

Geographic Information Systems Division
Department of Geography
University of Zurich - Irchel
Winterthurerstr. 190
CH-8057 Zurich, Switzerland

email: 	martin.tomko at geo.uzh.ch
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