Re: [Maxima-discuss] How can I catch this error? "errcatch" doesn't do the trick.

[Robert D. <rob...@gm...>]

On 2015-09-07, David Scherfgen <d.s...@go...> wrote:

> the following integral results in an error "quotient by zero":
>
> integrate(ev(ratsimp(1/(x^(5/2)+3*x^(1/3))),algebraic),x);
>
> Unfortunately, I can't catch the error using errcatch. It goes right
> through it, i.e. the whole evaluation is aborted, and I don't get any
> result (usually, errcatch would give me an empty list if it caught an
> error).

When "quotient by zero" is encountered, 'RAT-ERR is thrown, which blows
through 'catch' and 'errcatch'. I believe that's a bug.

A solution is to call RAT-ERROR-TO-MERROR in 'catch' and 'errcatch'. I
got that from TOPLEVEL-MACSYMA-EVAL. From what I can tell, that makes
'errcatch' work as expected for the above example (i.e., return an empty
list) and obviates the need for redefining MERROR.

best,

Robert Dodier

PS. Here is a patch.
diff --git a/src/suprv1.lisp b/src/suprv1.lisp
index d0c5fa4..be0a59f 100644
--- a/src/suprv1.lisp
+++ b/src/suprv1.lisp
@@ -770,14 +770,14 @@
 (defmspec $errcatch (form)
   (let ((errcatch (cons bindlist loclist)) ret)
     (if (null (setq ret (let (*mdebug*)
-			  (errset (mevaln (cdr form)) lisperrprint))))
+			  (errset (rat-error-to-merror (mevaln (cdr form))) lisperrprint))))
 	(errlfun1 errcatch))
     (cons '(mlist) ret)))
 
 (defmspec $catch (form)
   (let ((mcatch (cons bindlist loclist)))
     (prog1
-	(catch 'mcatch (mevaln (cdr form)))
+	(catch 'mcatch (rat-error-to-merror (mevaln (cdr form))))
       (errlfun1 mcatch))))
 
 (defmfun $throw (exp)