[Ocaml-lib-devel] Re: some proposals

[Alan P. <ap...@re...>]

In article <200...@ro...eak>, Michal Moskal wrote:
> 
> 1) For extList:
> 
> val partial_map : ('a -> 'b option) -> 'a list -> 'b list
> 
> let rec partial_map f = function
>  | x :: xs ->
>     begin
>       match f x with
>       | Some y -> y :: list_partial_map f xs
>       | None -> list_partial_map f xs
>     end
>  | [] -> []

The perl map function allows the number of outgoing items to be
other than 1, for instance:

  my @l2 = map { if ( filter( $_ ) { $_ } else {()}} @l1;

or:

  my %h = map { $_, f( $_ )} @l;

I imagine it would be a bit tricky to implement an Enum function like
that ("merge_map"?), but it would generalize the partial map function
above.


A more general question:  how many map/iterate functions will be a
part of the data structures, as opposed to having users stick to the
Enum versions?  For instance,

  List.map f l 

    vs

  List.of_enum (Enum.map f (List.enum l))

Will each datastructure have its own map function, to make things
convenient for users?