Re: [Caml-list] List.fold_left vs. Hashtbl.fold

[David House <dhouse@janestreet.com>]

This is a perfect example of why we wrote the core library:

  https://bitbucket.org/yminsky/ocaml-core/wiki/Home

In core, most of the iteration functions take their closure argument
as a labelled ~f. So you can say List.fold_left my_list ~f:my_func, or
List.fold_left ~f:my_func my_list.

This tiny syntactic cost allows you lay out code much more logically:
sometime you have a big long list, so you don't want the name of the
function lost somewhere, way down the page. Sometimes it's the other
way round, and you have a bit lambda that you're folding with, but you
don't want the name of the list to be some anonymous bit of text a
very long way away from the word "fold".

On Wed, Nov 28, 2012 at 4:40 AM, William Smith <bills@wwayneb.com> wrote:
> List.fold_left expects the List as the 3rd parameter with the second
> parameter being the initial value.
>
> Hashtbl.fold expects the Hasthbl as the second parameter with the 3rd
> parameter being the initial value... just the opposite of List.fold_left.
>
> Is there a reason for this difference?   I'm having trouble remembering
> which goes which way.   If it's not a historical accident, I'd like to have
> a understanding of why they are different to help me know which is which.
>
> Thanks,
>
> Bill
>
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