[Haskell-cafe] Combine list of sorted lists

[Quan Ta]

On 12/29/06, Neil Mitchell <ndmitchell at gmail.com> wrote:
>
> Hi
>
> >       f1 :: [Int] -> [[Int]]
> >        f1 []     = []
> >       f1 (a:as) = [a] : f1 as
>
> f1 is simply a map
>
> >       f3 la lb = let a = head la
> >                       b = head lb
> >                  in if sum a <= sum b then
> >                         a : f3 (tail la) lb
> >                      else
> >                         b : f3 la (tail lb)
>
> Why not use pattern matching to split up la and lb, rather than head/tail?
>
> I would have thought the whole function could be written as a nice
> foldr merge, where merge :: [Int] -> [Int] -> [Int]. Thats only a
> guess at the top of my head though, not worked out properly.
>
> Is this homework? If so its useful to state when you post the question :)
>
>
Hi Neil,

I am not sure how to express f1 with map?  how do I say
(lambda (ls)
    (map (lambda (x) (list x))
    ls))
in Haskell?  map ([])  ?

Here is my new f3:
f3 :: [[Int]] -> [[Int]] -> [[Int]]
f3 [] lb = lb
f3 la [] = la
f3 la@(a:as) lb@(b:bs) = if sum a <= sum b then
                             a : f3 as lb
                         else
                             b : f3 la bs

(btw, yes this is homework assigned by prof. Quan in quantum computing class
:))
Thanks,
Quan
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