How to use (catch)?

From: Ian Wild <ian.wild_at_eurocontrol.be>
Date: Thu, 01 Jul 1999 17:14:59 +0200

Unless I'm missing something, (catch) works a bit better
than I'd have hoped. It not only prevents the normal
error messages appearing, it hides any clue as to what
went wrong. For example:

Welcome to the STk interpreter version 3.99.4 [Linux-2.X-ix86]
Copyright 1993-1999 Erick Gallesio - I3S - CNRS / ESSI <eg_at_unice.fr>
STk> (open-input-file "not-there")
*** Error:
    could not open file: "not-there"
Current eval stack:
__________________
  0 (open-input-file "not-there")
STk> *last-error-message*
"could not open file"
STk> (catch (/ 1 0))
#t
;;;
;;; What I'd like at this point is something I
;;; can use to tell the user "divide by zero error"
;;; and then carry on. Instead I get:
;;;
STk> *last-error-message*
"could not open file"
;;;
;;; however, without the (catch), I get:
;;;
STk> (/ 1 0)
*** Error:
    /: not a valid number: 0
Current eval stack:
__________________
  0 (/ 1 0)
;;;
;;; and
;;;
STk> *last-error-message*
"/: not a valid number"



Digging through the sources, it seems *last-error-message*
is set as part of the message printing, when I'd prefer
it be done during the error catching.

The following patch seems to fix things (WARNING: on my
home machine - I don't have enough disc space currently
to try it out on this machine! In fact, I don't even have
space to untar the whole STk distribution.):

--- orig/error.c Thu Jul 1 13:35:13 1999
+++ new/error.c Thu Jul 1 13:36:13 1999
_at_@ -138,18 +138,19 @@
     }
   POP_ERROR_HANDLER;
 
- /*
- * Retain the arguments of this error in global Scheme variables
- */
   Flush(STk_curr_oport); Flush(STk_curr_eport);
- STk_define_variable("*last-error-message*", STk_makestring(message), NIL);
- STk_define_variable("*last-error-arg*", x, NIL);
 }
 
 
 void STk_err(char *message, SCM x)
 {
   STk_reset_eval_hook();
+
+ /*
+ * Retain the arguments of this error in global Scheme variables
+ */
+ STk_define_variable("*last-error-message*", STk_makestring(message), NIL);
+ STk_define_variable("*last-error-arg*", x, NIL);
 
  /* Print a message if the error is not ignored */
   if (!(STk_err_handler->context & ERR_IGNORED)) {





in other words, in error.c, take the last couple of lines
(and their associated comment) from print_message() and
move them down into STk_err().

Have I broken anything?
Have I missed a don't-mess-with-the-C way of
getting what I want?

imw
Received on Thu Jul 01 1999 - 17:15:55 CEST

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