Suppressing error message "-- an error. To debug this try: debugmode(true); "

2012/12/1 Robert Dodier <robert.dodier at gmail.com>

> On 2012-12-01, Stefano Ferri <ferriste at gmail.com> wrote:
>
> > As an alternative, I could print a message with "print" and then stop the
> > program in some way.... but is there such a "stop" or "exit" command
> > implemented?
>
> Well, from looking at src/merror.lisp there are various ways to handle
> errors. Probably the only way to get exactly what you want is to write a
> line or two of Lisp code.
>


I know pretty nothing about Lisp, but looking at merror.lisp I've created
and loaded a file "myerror.lisp" which simply redefines "merror":

(defun merror (sstring &rest l)
    (declare (special errcatch *mdebug*))
    (setq $error `((mlist) ,sstring ,@ l))
    (and $errormsg ($errormsg))
    (cond (*mdebug*
        (let ((dispflag t) ret)
        (declare (special $help dispflag))
        (format t (intl:gettext " -- an error. Entering the Maxima
debugger.~%~
            Enter ':h' for help.~%"))
        (progn
            (setq ret (break-dbm-loop nil))
            (cond ((eql ret :resume)
                (break-quit))))))
    (errcatch (error 'maxima-$error))
        (t
        (fresh-line *standard-output*)
        ($backtrace 3)
        (format t (intl:gettext "~%"))
        (throw 'macsyma-quit 'maxima-error))))


It is the same code of the original merror, except for the second to last
line in which

(format t (intl:gettext "~& -- an error. To debug this try:
debugmode(true);~%"))

has been replaced by a simple

(format t (intl:gettext "~%"))

which only prints a new line. It works perfectly but maybe it is a ugly
solution... How can I avoid to rewrite all the function and redefine only
the "format t (....." line?
Even if ugly, could it be a correct solution?



>  * assign ?errcatch:true and call error("my msg") as before. I see in
>    src/merror.lisp that that suppresses the bit about launching the
>    debugger.
>

It suppresses the  "-- an error. To debug this try: debugmode(true);", but
the output is even worse:

(%i24) error("my msg");

my msg
Maxima encountered a Lisp error:

my msg

Automatically continuing.
To enable the Lisp debugger set *debugger-hook* to nil.



>  * define your own function which uses Maxima's throw/catch mechanism.
>    E.g.: myerror (msg) := (print (msg), throw ('oops));
>    throw/catch is a nonlocal flow of control mechanism, maybe that's
>    what you want.
>


I'll look at this way too, but I would lose the information contained in
errormsg(), which sometimes is useful.

Thanks for your help.
Stefano