embedded functions

[John W. Eaton]

On 24-Mar-2006, Gorazd Brumen wrote:

| hi all,
| 
| does octave allows this in an function file:
| 
| function y = foo (x)
| 
|       ...blabla....
|       r = foo1( x)
| 
|       function z = foo1 (g)
|               ...blabla2...
|       endfunction
| 
| 
| endfunction
| 
| such that foo1 is visible only to foo1?

No.

Octave does provide subfunctions, but not nested functions.

FWIW, I think the addition of nested functions to Matlab without the
addition of away to specify local variables was a bad idea.  The
problem is that there is no other place in the language where the
scoping rules are similar, and without a way to declare local
variables, you are just asking for trouble.  It may seem nice for
nested functions to inherit the workspace(s) of the enclosing
function(s) but when the functions become large and have the functions
are small and there are only a few variables, but when the functions
get to be larger with many variables, it seems to me that it is just
too easy to introduce bugs.  For example, if you have

  function parent_fcn ()
    %% many variables defined and used here, including:
    some_variable = 1;

    %% now the call to nested function, which can see and modify all
    %% the variables in parent_fcn.
    nested_fcn ();

    %% more calculations with variables here, including
    a_calculation_with (some_variable);

    function nested_fcn ()
      %% Imagine this function initially does not touch any of the
      %% variables in parent_fcn.  But sometime later, it is modified
      %% with the addition of some_variable that happens to have the
      %% same names as some_variable in use in parent_fcn.  The function
      %% fails mysteriously.  It is hard to see why.  To avoid
      %% problems like this, you must know the entire list of variables
      %% used in parent_fcn before you can make any changes to
      %% nested_fcn.
    end

  end


jwe



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