[erlang-questions] foldl vs foldr and ++

Ulf Wiger <>
Fri May 11 11:27:29 CEST 2012

On 11 May 2012, at 04:02, Richard O'Keefe wrote:

> This can be written more efficiently, but it's best of all
> just not to reverse the string in the first place.  Keep
> the code at a level where you can see what's going on well
> enough to spot the really _big_ efficiency gains.

And this is of course the really important difference between
foldr() and foldl():

- in which order do you want to process the list?
- if you build a list in the accumulator, in which order do you want it?

For most practical purposes, one should assume that they 
both both do their job efficiently.


Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.

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