"fold": a replacement for "reduce"

[monarch_dodra]

On Thursday, 27 March 2014 at 14:41:19 UTC, Brian Rogoff wrote:
> 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.

Right, but what about "fold" vs "fold_left"? Is there a 
difference?