[Haskell-beginners] Help : foldl skipping one value in list

[Alexander V Vershilov]

Hello.

Wed, Nov 09, 2011 at 07:18:14AM +0200, Lev Broido wrote
> Hi
> I am implementing toy loop search algorithm in graph .
> I encountered strange problem -- it seems , that fold doesn't run on the 
> whole list .
> Code is at http://hpaste.org/53776
> Section in question is updVis function
> Problem occurs when _newStateMap_2 is being calculated
> Please advise.
> 
> Thanks,
> Lev
> 

I have not checked all pasted code but for your problem you can try
next solution (using Either to specify is it odd or even argument):

> f = foldl (\x y -> inner x y) (Left [])
>     where
>       inner (Left xs) _ = Right xs
>       inner (Right xs) y = Left (yourfunction y:xs)

--
Alexander V Vershilov
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