Re: [Ocaml-lib-devel] Proposal: List.map_reduce

[Jonathan R. <jon...@gm...>]

> fold_reduce? Do you mean fold? If not, then what does the fold_reduce
> you're thinking of look like?

Oops, sorry. fold is reduce :-) And I meant no, I don't think it's too
specialised.

I'm not sure about the name, as it's a fold that filters & maps
elements in a single step.

And in terms of readability and thinking about it some more, I don't
see why something like the following aren't suitable:

let a_total = List.fold_left (fun acc -> function `A x -> acc + x | _
-> acc) 0 list;;
let c_max = List.fold_left (fun acc -> function `C x -> max acc x | _
-> acc) min_int list;;
let b = List.fold_left (fun acc -> function `B x -> acc || x | _ ->
acc) false list;;

They all convey exactly what they're trying to achieve. Perhaps there
are more complicated cases in real life programming, but imo, I think
they're a little nicer, and probably more efficient than your
implementation.

> There is also precedent
> for this kind of thing -- see ExtList.filter_map.

I think this is different, as the naive approach of filtering, then
mapping can be considerably slower than combining the two.

Jonathan