%! /usr/NeWS/bin/psh

% NeWS error handler using the object browser (NeWS1.1)
%
% Jeremy Huxtable
%
% Mon Jul 25 17:36:06 BST 1988

% This file implements a NeWS error handler which allow you to actually
% read your error messages before they shoot of the top of your terminal
% emulator. When an error occurs, the error handler creates a dictionary
% containing useful information about the error and the current process
% and pops up a browser onto it.
% Thus when you get an error, instead of 546 lines of fast-moving text,
% you get a neat little window and can admire the error at your leisure.
% As well as this, you can of course follow all the links in the dictionary
% and find just where the error occurred.  If you are lucky, you might be
% able to break all the cyclic references to things and get rid of all
% those dead windows that tend to pile up during protracted debugging
% sessions.

% Bugs and missing features:
%       - There should be an execution stack browser thet lets you
%         see the execution stack in full, with the current operator
%         in bold print or something.
%       - I can't get this to load if I put it in my "user.ps" - I
%         get an error executing "acceptconnection" (interrupted
%         system call)!.

systemdict begin

% Change this path name to your own:-
systemdict /Browser known not { (ps/lib/browser.ps) run } if

/MyErrorDict dictbegin
    StandardErrorNames { {MyErrorHandler} def } forall
dictend def

/MyErrorHandler {
    % Must be careful with manipulating the stacks here, as otherwise
    % our private stuff will appear in the browser!
    /errordict OldErrorDict store
    pop % Get rid of the "offending command" from stack
    % create a dictionary of useful info. Note that we must get the
    % process' stacks now as otherwise they disappear when the "killprocess"
    % is done.
    currentprocess /DictionaryStack get
    7 dict begin
	/DictionaryStack exch def
	currentprocess /OperandStack get /OperandStack exch def
	/ExecutionStack
	    currentprocess /ExecutionStack get
	    0 1 index length 4 sub getinterval
	def % Remove this error handler from exec stack
	/Interests currentprocess /Interests get def
	/Error $error /errorname get def
	/Executing $error /command get def
	/Process currentprocess def
	currentdict
    end
    50 600 (Error) 4 3 roll
    framebuffer start_browser
    /errordict MyErrorDict store
    currentprocess killprocess
} def

/OldErrorDict systemdict /errordict known {errordict} {null} ifelse def
/errordict MyErrorDict def

end
% End of error handler code.