[parenscript-devel] Keyword arguments and quoted symbols in Parenscript

[Vladimir Sedach]

Hi Red,

> I have modified the behavior of keywords found in Parenscript source to be
> parsed into (PS-QUOTE keyword) instead of (JS-VARIABLE keyword).

The current behavior is (ps::compile-parenscript-form :baz) => :baz
(there's no quoting involved). The printer then outputs keyword
symbols as strings, since this is the closest analogue (a
self-evaluating object) to keywords among the native JavaScript
objects.

> This seems
> to make more sense because in Lisp, evaluating a keyword yields the keyword
> itself rather than the value bound to it.  As a result, the ability to paass
> keyword arguments to functions is now restored.
>
> CL-USER> (ps:ps (foo "bar" :quix "quo" :etc "etc..."))
> "foo('bar', { quix : 'quo', etc : 'etc...' });"
>
> Whereas this used to yield foo('bar', quix, 'quo', etc, 'etc...')

This is actually a fix to keyword argument handling: previously the PS
lambda-list handling code assumed that whenever it encountered a
keyword in the arglist of a function, it was the beginning of the
keyword portion of the lambda list, and started making the object at
that point. This of course may not be the case if you are trying to
use keywords as arguments to a function. With keywords compiled to
strings, you get self-evaluating objects and can do keyword handling
in the function body at runtime (which is what the current code does).

Thanks,
Vladimir

> In general, symbols occupy a strange place in Parenscript.  Javascript has
> no analogue of Lisp symbols, so there is no sensible translation of symbols
> that works for everyone.  Nonetheless, quoted symbols are used in many
> Parenscript macros to fake having real symbols in javascript.  We could
> build in the ability to translate symbols to some javascript form, e.g.
>
> (ps:ps (make-instance 'animal)) =>  makeInstance( symbolTable["ANIMAL"] )
>
> The latter part of this post is just food for thought.  I will go ahead and
> commit the patch for the former part of this post unless someone objects.
>
> Red
>
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