Re: is-a? implemented, possible bug.

From: Erick Gallesio <>
Date: Mon, 08 Jan 1996 09:26:27 +0000

> Clifford Beshers writes
> Well, I was wrong, class-direct-supers takes a class, not an instance,
> so the function I wanted is possible.
> In include it here, along with a mysterious transcript, which I think
> might reveal a bug in the STk interpreter.
> When I (load "isa.scm") the first time, is-a? gives the wrong answer,
> but if I load it again, it give the correct answer. Can anyone
> explain this as an error in my code?

This is not a bug. The problem arises because is-a? is a macro which is defined
in stklos.stk. It is defined as
        (define-macro (is-a? obj class)
          `(and (member ,class (class-precedence-list (class-of ,obj))) #t))
This definition is auto-loaded with your first define-class and it overloads
your definition. Thigs go wrong because of the parameter order which is
different between your is-a? and STklos one.
Second loading overload Stklos definition and things go well.

BTW, to answer to the initial question, is-a? is already defined in STklos ;-)

                -- Erick
Received on Mon Jan 08 1996 - 09:26:28 CET

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