[Haskell-beginners] Creating a Triple List from a List

[Francesco Ariis]

Il 27 febbraio 2021 alle 18:07 A. Mc. ha scritto:
> Hello,
> 
> What is the best way to take:
> [1, 2, 3, 4 ]
> 
> And convert it to:
> 
> [ [ [ 1 ], [ 2 ] ], [ [3]. [4] ] ]
> 
> so that each member pair is:
> 
> [ [1], [2] ]
> 
> roughly analogous to a 1x2 vector?

A 1×2 vector would be

> [[1  2], [3, 4]]

am I wrong? If so, a quick and dirty solution could be

    d2 :: [a] -> [[a]]
    d2 [] = []
    d2 [a] = error "odd element"
    d2 as = let (is, es) = splitAt 2 as
            in is : d2 es
    -- λ> d2 [1..6]
    -- [[1,2],[3,4],[5,6]]