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From: Lukasz Stafiniak <lukstafi@gmail.com>
Date: Wed, 28 Nov 2012 18:37:19 +0100
Message-ID: <CAJMfKEX37AtHzY_8o=L0LMH8PEMqeVRttn0vJQUYbiL7AGBx6Q@mail.gmail.com>
To: Gabriel Scherer <gabriel.scherer@gmail.com>
Cc: caml users <caml-list@inria.fr>
Content-Type: text/plain; charset=ISO-8859-1
Subject: Re: [Caml-list] List.fold_left vs. Hashtbl.fold

On Wed, Nov 28, 2012 at 6:25 PM, Gabriel Scherer
<gabriel.scherer@gmail.com> wrote:
>
> This means that fold_left may not exist for arbitrary data structure
> (think of binary trees), while fold_right is rather universal. Other
> folding functions in the standard library (in Set and Map in
> particular, but in Hashtbl as well) have therefore taken inspiration
> from the fold_right structure, rather than fold_left.

This is right, you get my "upvote". But Set and Map do not intend to
expose the structure of the underlying data structure to the folding
computation. The folds of Set and Map traverse the elements in a
sequential order. They could be a deforested variant of List.fold_left
composed with Set.elements.