From help-octave-request at bevo dot che dot wisc dot edu  Thu Oct  1 06:25:11 1998
Subject: functions within functions?
From: Ferdinand Schinagl <ferdi at roentgen dot hlphys dot uni-linz dot ac dot at>
To: help-octave at bevo dot che dot wisc dot edu
Date: Thu, 01 Oct 1998 12:14:28 +0100

Hi,

obviously it is not possible to define
functions within functions directly, like:

function a(x)
  function y = b(x)
    y = sin(x)
  end
end

However, as I found out, it can be done by
evaluating strings (at runtime then, of course):

function a(x)
  str = sprintf("function y = b(x); y = %e*sin(x); end;",x)
  eval(str);
end

or by means of writing into an external file
which then contains all the necessary information:

function a(x)
  handle = fopen("b.m","w");
  fprintf(handle,"function y = b(x)\n  y = %e*sin(x);\nend",x);
  fclose(handle);
end

Well, both solution do not work when a is called
from another function, at least to a certain extent:

First, when defining b by 'eval':

function c(x)
  for i=1:3
#    clear b;
    a(i);
    b(x)
  end
end

fails as long as I don't clear b (remove the comment and
you'll see what happens).

Second, b defined via file (by 'fprintf') takes some time
until b is recognized the way it is defined. Just type

octave:70> a(1);b(1)
ans = 0.84147
octave:71> a(2);b(1)
ans = 0.84147
octave:72> a(2);b(1)
ans = 1.6829       

The only difference between :71> and :72> is the amount
of time that's gone. If you wait for a secon or so,
you get :72>, if you invoke a(2);b(1) immediately after
a(1);b(1) one gets :71>!

You can (perhaps only) avoid this using:

a(1);source("b.m");disp(b(1));a(2);source("b.m");disp(b(1))

Are there any concerns?

Best regards,
Ferdinand.