[Haskell-beginners] ignature for a list of a set length

Martin Tomko martin.tomko at geo.uzh.ch
Tue Sep 28 11:39:50 EDT 2010

I like this suggestion, I will give it a go!
thanks, and also for the catMaybes function, I needed something like 
that some days ago.

On 9/28/2010 5:20 PM, edgar klerks wrote:
> I think it is simpler to use the Maybe type for this. If you only  
> search for ternary relations, you can write a function, which only 
> converts a list to a 3-tuple if it is of length three and otherwise it 
> returns nothing. Then with catMaybes :: [Maybe a] -> [a], you can 
> convert it back to a list with only 3-tuples.
> import Data.Maybe
> getLengthThree = catMaybes . fmap toTup
>     where toTup (x:y:z:[]) = Just (x,y,z)
>           toTup _ = Nothing

Martin Tomko
Postdoctoral Research Assistant

Geographic Information Systems Division
Department of Geography
University of Zurich - Irchel
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