Re: Nested Functions alternative?

[Jason Carver]

Ok, great, it's the 'persistent' keyword that I was missing.  Thanks!

BTW, I got the Matlab nested function syntax from the zip file here: http://www.mathworks.com/matlabcentral/fileexchange/18223

My code was consistent with that zip I think, so I'm not sure why it wouldn't work.

Also, the sneakemail servers mangle the headers to make it look like it was only sent to you, even though I cc'd address@hidden .  Anyway I messed up the last time and posted my "real" email for spammers everwhere, so for clarity I stopped using sneakemail on this reply.

Thanks for all your help Carlo,

Carver

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On Mon, Jun 22, 2009 at 11:58 AM, Carlo de Falco carlo.defalco-at-gmail.com |public mailing list| <address@hidden> wrote:

On 22 Jun 2009, at 16:52, address@hidden wrote:

Thanks Carlo,

I believe that solution won't work in general for a "stateful generator" pattern, right?  eg~

==anonymous function:

function a = adder(a,b)
 a = a+b;
end

gen = @(b) adder(0,b) #anonymous function does not maintain state between calls

gen(1) -> 1
gen(1) -> 1
gen(1) -> 1

==nested function

function f = adder(a)
 #adder returns a stateful adding function that keeps track of the total sum
 function a = addon(b)
 #addon adds b into the summation with each call, returning the cumulative sum over all calls
 a = a+b; #assign to state variable a
 end
 f = @addon
end

gen = adder(0) #nested function maintains state between calls

gen(1) -> 1
gen(1) -> 2
gen(1) -> 3

==

Is it possible to accomplish the same effect as the nested function in Octave?  Despite the maintainers' (reasonable) warnings about code clarity, there are some situations that would really benefit from this pattern.  (Apologies if my nested function example has any typos, I don't have access to Matlab to test it)

Thanks,
Carver

Again maybe I'm missing the big picture as I don't understand why you would need nested functions to accomplish what you propose, but I think you can doit as follows:

>>function f = adder (a, b)
 persistent f = b;
 f += a;
endfunction
>> gen = @(a) adder(a, 0);
>> gen (1)
ans =  1
>> gen (1)
ans =  2
>> gen (1)
ans =  3

HTH,
c.

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