How to implement Data.Map.insertList*?

[Keean Schupke]

Would it not be more efficient to put the list into a new map, and then 
merge the old and new maps (a bit like
the sort and merge technique used in old tape databases)...

    Keean.


Mirko Rahn wrote:

>
> The old FiniteMap module contains the addListToFM* functions that are 
> missing in Data.Map. But how to implement it?
>
> First answer:
>
> insertList_foldl :: Ord k => [(k,a)] -> Map.Map k a -> Map.Map k a
> insertList_foldl = flip (foldl ins) where fluc = flip . uncurry
>                       ins  = fluc Map.insert
>
> Second answer:
>
> insertList_union :: Ord k => [(k,a)] -> Map.Map k a -> Map.Map k a
> insertList_union kas = Map.union (Map.fromList kas)
>
> Situation and Problem:
>
> We already have a map of size n and want to insert a list with m 
> elements. Then we look at the documentation and one gets:
>
> * For the first answer we do need O(sum_{i=0}^{m-1}log(n+i)) = 
> O(log((m+n)!/n!)) operations.
> * For the sencond answer we do need O(m*log(m))+O(n+m) = 
> O(m*log(m)+n+m) operations.
>
> These terms are hard to compare but a plot shows that insertList_foldl 
> should be faster than insertList_union.
>
> But a testprogram shows that insertList_union is faster (and needs 
> less memory) whatever the sizes of n and m are.
>
> So my questions are:
>
> Why are the insertList* functions missing?
> How would the library implementors implement insertList* and why?
>
> thanks,
>