## Copyright (C) 2000-2011 Paul Kienzle
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {} demo ('@var{name}', @var{n})
##
## Runs any examples associated with the function '@var{name}'.
## Examples are stored in the script file, or in a file with the same
## name but no extension somewhere on your path.  To keep them separate
## from the usual script code, all lines are prefixed by @code{%!}.  Each
## example is introduced by the keyword 'demo' flush left to the prefix,
## with no intervening spaces.  The remainder of the example can contain
## arbitrary Octave code.  For example:
##
## @example
## @group
##    %!demo
##    %! t=0:0.01:2*pi; x = sin(t);
##    %! plot(t,x)
##    %! %-------------------------------------------------
##    %! % the figure window shows one cycle of a sine wave
## @end group
## @end example
##
## Note that the code is displayed before it is executed, so a simple
## comment at the end suffices.  It is generally not necessary to use
## disp or printf within the demo.
##
## Demos are run in a function environment with no access to external
## variables.  This means that all demos in your function must use
## separate initialization code.  Alternatively, you can combine your
## demos into one huge demo, with the code:
##
## @example
##    %! input("Press <enter> to continue: ","s");
## @end example
##
## @noindent
## between the sections, but this is discouraged.  Other techniques
## include using multiple plots by saying figure between each, or
## using subplot to put multiple plots in the same window.
##
## Also, since demo evaluates inside a function context, you cannot
## define new functions inside a demo.  Instead you will have to
## use @code{eval(example('function',n))} to see them.  Because eval only
## evaluates one line, or one statement if the statement crosses
## multiple lines, you must wrap your demo in "if 1 <demo stuff> endif"
## with the 'if' on the same line as 'demo'.  For example:
##
## @example
## @group
##   %!demo if 1
##   %!  function y=f(x)
##   %!    y=x;
##   %!  endfunction
##   %!  f(3)
##   %! endif
## @end group
## @end example
## @seealso{test, example}
## @end deftypefn

## FIXME: modify subplot so that gnuplot_has_multiplot == 0 causes it to
## use the current figure window but pause if not plotting in the
## first subplot.

function demo (name, n)

  if (nargin < 1 || nargin > 2)
    print_usage ();
  endif

  if (nargin < 2)
    n = 0;
  endif

  [code, idx] = test (name, "grabdemo");
  if (length (idx) == 0)
    warning ("demo not available for %s", name);
    return;
  elseif (n >= length (idx))
    warning ("only %d demos available for %s", length (idx) - 1, name);
    return;
  endif


  if (n > 0)
    doidx = n;
  else
    doidx = 1:length(idx)-1;
  endif
  for i = 1:length (doidx)
    ## Pause between demos
    if (i > 1)
      input ("Press <enter> to continue: ", "s");
    endif

    ## Process each demo without failing
    try
      block = code(idx(doidx(i)):idx(doidx(i)+1)-1);
      ## Use an environment without variables
      eval (cstrcat ("function __demo__()\n", block, "\nendfunction"));
      ## Display the code that will be executed before executing it
      printf ("%s example %d:%s\n\n", name, doidx(i), block);
      __demo__;
    catch
      ## Let the programmer know which demo failed.
      printf ("%s example %d: failed\n%s\n", name, doidx(i), __error_text__);
    end_try_catch
    clear __demo__;
  endfor

endfunction

%!demo
%! t=0:0.01:2*pi; x = sin(t);
%! plot(t,x)
%! %-------------------------------------------------
%! % the figure window shows one cycle of a sine wave