[Openmcl-devel] lambda-gtk question on OpenMCL
Andrew P. Lentvorski, Jr.
bsder at mail.allcaps.org
Thu Jan 27 01:02:59 UTC 2005
On Jan 26, 2005, at 6:16 AM, Rick Taube wrote:
> both sbcl and cmucl return pointer args as multiple values. so in
> the example above the NIL first return value is the value returef by
> the function the second and third values are the pointer arg values
> the function produces.
Sure. But that return list is dependent upon the number of parameters
that are actually pointers, right? Thus:
int nasty(void *, int, int *, int, int *, int)
would return something like
And I would actually have to hunt down the original header file to work
out what corresponds with what. Sure, that's okay if it looks like
above, but if the signature in the API docs is:
GBoolean nasty(GC, GBoolean, FontHandle, FontNumber, ClosestFontHandle,
Things get really bad. Effectively, I have an unchecked function
signature encoded in the logic of my program. All manner of silent bad
things will happen if that signature ever alters.
Additionally, if I write something like:
(widget-get-size-request widget 100 100) when I really meant
(widget-set-size-request widget 100 100), I get no complaints under the
> If there is a better way to handle situations like this please let me
> know, but only if it can determined from ffigen expressions and only
> if it works in all three lisps.
Well, I kinda hate to suggest this for lisp, but I think I'd rather see
the calls actually alter the input arguments rather than have
positional multiple return values with no annotation or checks. For
example in OpenMCL (please have someone with a lot more macro writing
experience check this):
(defmacro my-drawable-get-size (drawable height width)
`(rlet ((r1 :int ,height)
(r2 :int ,width))
(let ((z (#_gdk_drawable_get_size ,drawable r1 r2)))
(setf ,height (%get-signed-long r1))
(setf ,width (%get-signed-long r2))
Which results in something like this in OpenMCL:
? (setq h0 -1001)
? (setq w0 -455)
? (my-drawable-get-size dr w0 h0)
;Compiler warnings :
; Undeclared free variable DR, in an anonymous lambda form.
; Undeclared free variable W0 (2 references), in an anonymous lambda
; Undeclared free variable H0 (2 references), in an anonymous lambda
? (my-drawable-get-size dr 100 100)
> Error in process listener(1): 100 is not a symbol.
While this results in destructive side effects, calling Gtk can always
result in destructive side effects. In addition, people can now create
wrappers in lisp which can do things like copy the arguments, check for
modification, rewrap things for multiple values, etc. without having to
worry about position.
I assume that this kind of thing would be portable across the various
lisps, but someone with more knowledge than I would have to check that.
> so in the case of a function that only produces values the external
> args you pass are useless.
Actually, Gtk has the rather nasty issue that the values of args can
alter the functionality of the function.
_gdk_drawable_get_size is allowed to take a NULL pointer and not return
that dimension. Consequently, gdk::drawable-get-size will likely
segfault on the OpenMCL call to %get-signed-long. I presume similar
behavior on the other lisps.
This kind of thing is really crummy and it means that eventually there
will have to be some way to handle hand coded exceptions. However,
this is orthogonal to the value returning questions.
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