"fold": a replacement for "reduce"

[Brian Rogoff]

On Thursday, 27 March 2014 at 13:23:27 UTC, monarch_dodra wrote:
> On Thursday, 27 March 2014 at 12:48:41 UTC, Simen Kjærås wrote:
>> Your new fold (foldl? Should we have foldr as well?)
>
> "fold" (from what I understood) is what you call "foldl". It 
> was discussed to not introduce "foldr", as it's just 
> "fold!(binaryReverseArgs!Fun)(range.retro);".
>
> I'm not sure I was able to understand what the difference 
> between "fold" and "foldl" is...

In functional languages,

fold_left(f, a, [b1, ..., bn]) is
f((... (f, (f, a, b1), b2) ...), bn)

as you can see, the innermost f call is on the leftmost sequence 
element, and

fold_right(f, [a1, ..., an], b) is
f(a1, (f a2 (... f(an, b) ...)))

That's how I think of them.