[erlang-questions] The history of recursion in languages. Any stories from erlang?

[Bhasker Kode]

yes, here the number of cores and schedulers comes in to play.

foo()->
  io:format("."),
  foo().

bar()->
  io:format("x"),
  bar().

1>  [spawn(fun()-> fuconf:X() end) || X <- [foo,bar] ].
.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.xxx..xx.x.x.xx.xxx.xxxx.xxx.xxxxx.x.xxx.xxx.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.xxxxxxxxxxxxxxxxxxxxxxxxxxx[<0.34.0>,<0.35.0>]
x.xxxxxxxxxxxxxxxxxxxx.xxxxxx.x.x.x.x.x.x.x..x.xx.x.x.x.x.x.x..x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x................x..............x................x......................x.........................x..............x.............x...............x..............x..............x..x.x.x.x.x.x.x.x.xx.x.x.xxx.x.xx.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.

So the erlang scheduler did not choke. It split work between the two
processes based on the number of reductions.

You can test out ^ by calling https://github.com/bosky101/fuconf
my slides are at http://www.slideshare.net/bosky101/recursion-and-erlang
I'm done with my talk at FunctionalConf, there was also a talk on APL
by Dyalog CTO Morten Kromberg.

Thanks everyone :) This was very educational.

~Bosky | @bhaskerkode

On Fri, Oct 10, 2014 at 6:43 AM, zxq9 <zxq9@REDACTED> wrote:
> On Thursday 09 October 2014 19:29:56 you wrote:
>> another erlang specific question.
>>
>> foo()->
>>   foo().
>>
>> bar()->
>>   receive
>>       X ->
>>          bar()
>>   end.
>>
>> both the above functions are tail-call optimized and happen to be recursive.
>>
>> if i run foo(), would its callstack remain unchanged? will beam bring it
>> down? how does it compare with the procedural while (1) { //do something }
>
> foo() -> foo(). behaves the same as while(1) {};. Testing just now, the stack
> indeed remains constant (at ~2.5k), and checking with Observer on the system
> I'm sitting at now shows around 4 billion reds per update. Beam will not bring
> down a simple infinite loop like this unless you tell it to (its performing as
> intended, why kill it if the user wanted it?).
>
> Its sort of interesting, with regard to scheduling not recursion, to spawn a
> few more of these than  you have cores, and then run something else and watch
> the EVM schedule around all the blank load.
>
> With regard to the original line of this thread...
>
> Richard O'Keefe, in a line of private emails, has convinced me that while
> recursion is at the root of computing theory, the concept was almost
> completely unknown in commercial languages until sometime in the (probably
> very late) 60's, and still not very well accepted outside AI research until a
> bit later.
>
> He demonstrated to me that the world of computing theory and AI research,
> being full of recursive definitions from the beginning (Lovelace -- with a
> unique notation for "cycles of cycles", Church, Gödel, etc.), had shockingly
> little impact on the tradition of language design that brought us to where we
> are today. In particular, it played no role in informing commercial hardware
> development and that led to an almost deliberate aversion to the subject by
> language designers working for those companies.
>
> Richard O'Keefe wrote:
>> APL (designed through 1960-1965)
>> could do recursion, but it was interpreted, and was and
>> remained, like Lisp, a niche language irrelevant to
>> nearly all programmers.  PL/I supported recursion, which
>> like much else it copied from Algol 60, but it was
>> regarded as strange, scary, and rare, and you had to
>> explicitly write, e.g.,
>>
>>    factorial:
>>       procedure (n) options (recursive);
>>
>>          if n < 2 then return 1;
>>          else return n * factorial (n-1);
>>
>>       end;
>>
>> Programming textbooks warned people not to use this feature
>> because it was too inefficient
>
> This makes me feel that we are still only rediscovering ideal ways to
> communicate with our computers and haven't yet come up with anything really
> new (some of the ideal notational concepts go as far back as Ada Lovelace's
> notes!). I'd always thought that developments in theory/research were
> influential in industry, but this  was clearly not the case.
>
> I'd like to thank Richard for taking the time to so thoroughly prove my
> assumptions wrong. It was really interesting!
>
> -Craig
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