<div dir="ltr">I tweaked your module to run via escript (just adding a simple main/1 and printing out the results of timer:tc), and I see a bit gap between foldl and foldr, whilst the hand coded version based on lists:reverse/1 is plenty fast enough:<br><br>t4@iske:test $ escript lr.beam 10000000<br>foldl: 679.103ms<br>foldr: 43609.149ms<br>reverse: 909.946ms<br>t4@iske:test $ evm info<br>R16B03 compiled for x86_64-apple-darwin11.4.2, 64bit <br><br>On Friday, 11 May 2012 10:27:29 UTC+1, Ulf Wiger  wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;">

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

<br>

<br>> This can be written more efficiently, but it's best of all

<br>> just not to reverse the string in the first place.  Keep

<br>> the code at a level where you can see what's going on well

> enough to spot the really _big_ efficiency gains.

<br>

<br>And this is of course the really important difference between

<br>foldr() and foldl():

<br>

- 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?

<br>

<br>For most practical purposes, one should assume that they 

both both do their job efficiently.

<br>

<br>BR,

<br>Ulf

<br>

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

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<br>

<br>

<br>

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