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+## Copyright (C) 2000 Paul Kienzle
+##
+## This program 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 2 of the License, or
+## (at your option) any later version.
+##
+## This program 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 this program; if not, write to the Free Software
+## Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+## 02110-1301  USA
+
+## -*- 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
+##    %!demo
+##    %! t=0:0.01:2*pi; x = sin(t);
+##    %! plot(t,x)
+##    %! %-------------------------------------------------
+##    %! % the figure window shows one cycle of a sine wave
+## @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
+##
+## 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
+##   %!demo if 1
+##   %!  function y=f(x)
+##   %!    y=x;
+##   %!  endfunction
+##   %!  f(3)
+##   %! endif
+## @end example
+##
+## @end deftypefn
+## @seealso{test, example}
+
+## TODO: modify subplot so that gnuplot_has_multiplot == 0 causes it to
+## TODO: use the current figure window but pause if not plotting in the
+## TODO: first subplot.
+
+## PKG_ADD: mark_as_command demo
+
+function demo(name, n)
+
+  if (nargin < 1 || nargin > 2)
+    usage("demo('name')  or demo('name, n)");
+  endif
+
+  if (nargin < 2)
+    n = 0;
+  endif
+
+  [code, idx] = test (name, 'grabdemo');
+  if (length(idx) == 0)
+    warning(["demo not available for ", name]);
+    return;
+  elseif (n >= length(idx))
+    warning(sprintf("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(["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", 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