Re: a puzzle...

[Ben Abbott]

On Feb 4, 2012, at 4:07 AM, Muhali wrote:

> ok, here is a real puzzle.
> 
> Put into a new directory these 4 files:
> 
> -----------------
> # foo.m
> global gfun
> gfun = @fC ;
> y = fA(e)
> -----------------
> # fA.m
> function y = fA (x, f)
>   global gfun
>   if nargin < 2
>      y = fA(x, gfun) ;
>   else
>      w = feval(f, x) ;
>      y = feval("fB", w) ;     #  <---  this is crucial
>   endif
> endfunction
> -----------------
> # fB.m
> function y = fB (x) y = x ; endfunction
> -----------------
> # fC.m
> function y = fC (x) y = x ; endfunction
> -----------------
> 
> From that direcotry, assuming '.' is in the path, you get:
> 
> %> octave -q foo.m
> y =  2.7183
> 
> Nice. But when in fA.m '"fB"' is replaced by '@fB' one gets
> 
> %> octave -q foo.m
> error: `w' undefined near line 7 column 22
> error: evaluating argument list element number 2
> error: called from:
> error:   /home/muhali/fA.m at line 7, column 9
> error:   /home/muhali/fA.m at line 4, column 9
> error:   /home/muhali/foo.m at line 3, column 3
> 
> Why is that?
> 
> M.

I ran your example from Octave's command line.  With ..,

        y = feval ("fB", w);

... and with ...

        y = feval (@fB, w);

... I obtained the same result.

        y =  2.7183

I'm running a recent tip.

Did you include the single-quotes, like below ?

        y = feval ('@fB', w);

What version of Octave are you running ? Do you get the same result from 
Octave's command line as when you run from your shell's prompt.

Ben