Proposal: strictify foldl'

[Henning Thielemann]

On Mon, 3 Nov 2014, Niklas Hambüchen wrote:

> On 03/11/14 17:59, Henning Thielemann wrote:
>> I would prefer a strict foldl provided by the
>> deepseq package and deprecate foldl' in favor of deepseq:foldl. This new
>> foldl could immediately implement the unconditional strictness for the
>> initial accumulator value.
>
> This has the problem though that `deepseq` will traverse the entire
> structure, and while seq traversals are quite fast, if done n times it
> will still take n*n time

If 'seq' is faster than 'deepseq' it leaves things unevaluated and thus 
builds up unevaluated expressions, right?


> What I mean to say is: Using `deepseq` in `foldl'` might forbid you to
> write some recursive code, e.g. in the cases where you call an outer
> foldl' on something whose substructure you used foldl', like when you
> use foldl' to fold up a tree from the leaves up.

I can't follow. :-( Do you have an example?