[drakma-devel] Conditional (#+/#-) expressions in DRAKMA
Hello, With the new release of DRAKMA I was looking over some of the source, and came across code like (some-function ...#+:clisp #+:clisp :clisp-arg clisp-val) which I'd never seen before. I started to investigate, and a discussion even started on c.l.l [1]. It turns out that not all Lisps treat these constructions in the same way. Particularly, in the case of #-feature #-feature, some process the second #-feature with *READ-SUPPRESS* bound to T, so the behavior is like #-CL:NIL. At any rate, it seems a bit safer and more portable not to nest the conditionalized expressions. The only place I found these was in request.lisp, and even there only in three places. I've attached a diff in which they are changed to the safer form. I've also added leading colons to openmcl, since the rest of the source seemed to use that style. Thanks for a great HTTP client—DRAKMA's the one I turn to when I need a Lisp HTTP client. //JT [1] http://groups.google.com/group/comp.lang.lisp/browse_thread/thread/8d50284a2... -- ===================== Joshua Taylor tayloj@cs.rpi.edu, jtaylor@alum.rpi.edu "A lot of good things went down one time, back in the goodle days." John Hartford
On Wed, Mar 4, 2009 at 4:10 AM, Joshua TAYLOR <tayloj@cs.rpi.edu> wrote:
With the new release of DRAKMA I was looking over some of the source, and came across code like
(some-function ...#+:clisp #+:clisp :clisp-arg clisp-val)
which I'd never seen before. I started to investigate, and a discussion even started on c.l.l [1]. It turns out that not all Lisps treat these constructions in the same way. Particularly, in the case of #-feature #-feature, some process the second #-feature with *READ-SUPPRESS* bound to T, so the behavior is like #-CL:NIL. At any rate, it seems a bit safer and more portable not to nest the conditionalized expressions. The only place I found these was in request.lisp, and even there only in three places.
I've attached a diff in which they are changed to the safer form. I've also added leading colons to openmcl, since the rest of the source seemed to use that style.
Thanks for the patch. I'm aware of the theoretical implications of this usage, but is it actually a problem in practice, i.e. does the code break for one of the supported Lisps? And, without reading the c.l.l discussion, is this maybe because the Lisp in question is not following the standard correctly? I'd be willing to accept the patch although I like the current form more, but it'd be nice to know what we really lose or win. Also, could you please resend the patch as a unified diff and without tab characters? http://weitz.de/patches.html Thanks, Edi.
On Wed, Mar 4, 2009 at 3:22 AM, Edi Weitz <edi@agharta.de> wrote:
On Wed, Mar 4, 2009 at 4:10 AM, Joshua TAYLOR <tayloj@cs.rpi.edu> wrote:
With the new release of DRAKMA I was looking over some of the source, and came across code like
(some-function ...#+:clisp #+:clisp :clisp-arg clisp-val)
which I'd never seen before. I started to investigate, and a discussion even started on c.l.l [1]. It turns out that not all Lisps treat these constructions in the same way. Particularly, in the case of #-feature #-feature, some process the second #-feature with *READ-SUPPRESS* bound to T, so the behavior is like #-CL:NIL. At any rate, it seems a bit safer and more portable not to nest the conditionalized expressions. The only place I found these was in request.lisp, and even there only in three places.
I've attached a diff in which they are changed to the safer form. I've also added leading colons to openmcl, since the rest of the source seemed to use that style.
Thanks for the patch. I'm aware of the theoretical implications of this usage, but is it actually a problem in practice, i.e. does the code break for one of the supported Lisps? And, without reading the c.l.l discussion, is this maybe because the Lisp in question is not following the standard correctly?
The /present/ code does /not/ break for any of the supported Lisps. However, I do see conditionalizations on :openmcl, and it's openMCL/ClozureCL that has this problem: CL-USER> (lisp-implementation-version) "Version 1.3-RC1-r11719M (DarwinX8664)" CL-USER> (lisp-implementation-type) "Clozure Common Lisp" CL-USER> (list #+:openmcl #+:openmcl 1 2 3 4) (1 2 3 4) CL-USER> (list #-:openmcl #-:openmcl 1 2 3 4) (2 3 4) ; I bet you weren't expecting this ^_^ This issue doesn't arise directly in the current code, but will come up if #-:openmcl #-:openmcl ever arises. This is just an attempt to make that less likely to happen (since it would differ from the surrounding style).
I'd be willing to accept the patch although I like the current form more, but it'd be nice to know what we really lose or win.
As above, it's really not a significant issue, and you'd probably be fine staying with the existing convention. The folks on c.l.l seem to agree that the last form is permissible by the standard. (I did send a message to the CCL people too, though, since there was a related bug, and they're doing something different than what many people have come to expect.)
Also, could you please resend the patch as a unified diff and without tab characters?
My apologies--I've even read that page before! I missed the `diff -u', and I'd assumed that Emacs/Slime wasn't putting in literal #\Tab characters (now something of which I'll have to be aware in the future). Updated diff attached. Again, the cost of non-adoption is very low, and benefits are only preventing /possible/ /future/ bugs. //JT
participants (2)
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Edi Weitz -
Joshua TAYLOR