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

[Francois Berenger <berenger@riken.jp>]

On 11/29/2012 01:21 AM, David House wrote:
> 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.

For those who only need labels, there are:

Module MoreLabels.Hashtbl
http://caml.inria.fr/pub/docs/manual-ocaml/libref/MoreLabels.Hashtbl.html

and

Module ListLabels
http://caml.inria.fr/pub/docs/manual-ocaml/libref/ListLabels.html

> 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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>