curious about feature expressions [was: RE: [Openmcl-devel] OpenMCL 1.0-rc1

[James Anderson]

hello;

i've often wonder about such conditionalizations, but have also wondered

1. why one would need to use them - in that the feature expression already
allows boolean combinations, and

2. where the spec defines their interpretation.

i tried again, following the below pointer, but also still found neither an
example nor an explanation.

...

> -----Original Message-----
> From: openmcl-devel-bounces at clozure.com
> [mailto:openmcl-devel-bounces at clozure.com]On Behalf Of bryan o'connor
> Sent: Monday, September 26, 2005 00.13
> To: OpenMCL Devel; Bill Clementson
> Subject: Re: [Openmcl-devel] OpenMCL 1.0-rc1
>
>
> >        (make-instance #+sbcl #-sb-thread 'bc-sbcl
> >               #+sbcl #+sb-thread 'bc-sbcl
> >               #-sbcl 'bc
> >               :slot1 "test"))
>
> the way reader conditionals work has changed since 0.14.3
> to properly handle "nested" conditionals like above.
> the "inside" conditional now gets properly evaluated.
>
> if sb-thread is not in *features*, your above form becomes:
>
>    (make-instance #+sbcl 'bc-sbcl
>                   #+sbcl
>                   #-sbcl 'bc
>                   :slot1 "test")
>
> then with sbcl not in *features* becomes:
>
>    (make-instance :slot1 "test")
>
>
> here's a version that should work:
>
>    (make-instance #+sbcl #+sb-thread 'bc-sbcl
>                          #-sb-thread 'bc-sbcl   ; same as above?
>                   #-sbcl 'bc
>                   :slot1 "test")
>
> this is either covered in 2.4.8.17 or the sections to which
> it refers.
>
>      ...bryan
>
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