[erlang-questions] '--' BIF to be used with caution?

Hynek Vychodil <>
Tue Jan 13 17:02:59 CET 2009

'--' have O(N.M) complexity, if you suspect big M use you own O(M+N.logM)
implementation. Do not use '--' for big M.

2009/1/13 Malcolm Dowse <>

> Hello,
> I ran into an issue with Erlang the other day. I'm not sure if it's a bug,
> but I thought I should warn others.
> I was using '--' to get the difference between two large lists. As expected
> it was very slow, but, to my surprise, ERTS became completely unresponsive
> for a long time. (Only one CPU was maxed out, and there was still plenty of
> memory available.)
> To reproduce (on Ubuntu 7.x, R12B-x), open an Erlang shell and type:
> spawn(fun() -> lists:seq(1,1000000) -- lists:seq(1,1000000,2) end).
> The unresponsiveness seems to be caused by '--' being a BIF. Is there a
> good reason for making it a BIF if it's not always an improvement?
> All the best,
> Malcolm
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--Hynek (Pichi) Vychodil

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