Re: [Sbcl-devel] Mysterious setf function behavior

[Christophe R. <cs...@ca...>]

Jason Dagit <da...@cs...> writes:

> I haven't been able to find a simple example to recreate my problem,
> but in my program I have code roughly of the form below:
> [...]
> debugger invoked on a UNDEFINED-FUNCTION in thread 31583:
>   The function (SETF A-SLOT1) is undefined.

In this context, this usually means that you have compiled a call to
(setf (a-slot1 ...) ...) before the defsetf has been seen.  If no
defsetf has been seen, the compiler will generate a call to 
#'(setf a-slot1).

In other words, this:

  (defsetf a-slot1 set-a-slot1)
  (defun foo ()
    ...
    (setf (a-slot1 a) b)
    ...)

is not equivalent to this:

  (defun foo ()
    ...
    (setf (a-slot1 a) b)
    ...)
  (defsetf a-slot1 set-a-slot1)

The first will behave as you expect, while the second will generate a
run-time undefined function error.

Cheers,

Christophe