On Sat, 2 Sep 2006, John Resig wrote:
>> Lately I've been experimenting with Parenscript, which is a
>> Lisp-to-JavaScript translator that allows you to write macros; if
>> anyone's interested I can post some sequencing macro code I've been
>> working on...
>
> Go ahead! I'm interested :-)
Right on.
So, for a simple example, here's a snippet of Parenscript code that
creates a DIV, puts some text in it, and fades it in, out, and back in
again:
(.append #$"body" (html ((:div :id "mydiv"
:style (css-inline :background "white"))
"Hello, world!")))
(seq
(.fade-in #$"div #mydiv" "slow")
(.fade-out #$"div #mydiv" "slow")
(.fade-in #$"div #mydiv" "fast")))
A few notes about the syntax: The "#$" is a reader-macro I wrote for for
convenience; #$"body" gets transformed into ($ "body"). I haven't yet
decided if this is a good thing or not. ;) In Parenscript, functions that
start with a "." such as ".append" and ".fade-in", above, are treated as
method calls. Capitalization is translated by Parenscript from Lisp-style
to JavaScript-style, which is why the jQuery methods end up looking like
".fade-in". The "html" and "css-inline" macros are part of Parenscript,
and allow you to generate JavaScript that builds HTML and CSS from
s-expressions.
The sequencing macro is "seq". The above "seq" call gets transformed into
the following:
(.fade-in #$"div #mydiv" "slow"
(lambda ()
(.fade-out #$"div #mydiv" "slow"
(lambda ()
(.fade-in #$"div #mydiv" "fast")))))
The resulting JavaScript is this:
function main() {
$('body').append('<div id="mydiv" style="' + ('background:white')
+ '">Hello, world!</div>');
$('div #mydiv').fadeIn('slow',
function () {
$('div #mydiv').fadeOut('slow',
function () {
$('div
#mydiv').fadeIn('fast');
});
});
}
So, this has similar effects to what I think you're trying to achieve with
method chaining, but is more general because you are not limited to a
single jQuery object for the dispatch of each chained operation.
Here's my working definition of "seq":
(defjsmacro seq (&rest forms)
(labels
((aux (lst)
(cond
((null lst) nil)
((and (consp lst) (not (cdr lst))) (car lst))
(t (append (car lst) (list `(lambda () ,(aux (cdr lst)))))))))
(aux forms)))
I'd like to extend it to allow inserting ordinary code in the middle of
the sequence with a "par" construct - I'm lifting this terminology out of
an interesting but obscure concurrent language called Occam:
http://en.wikipedia.org/wiki/Occam_programming_language
Ironically, in an event-driven model, "par" is really the default
behavior. When working with background functions, everything is parallel;
you have to really work at making things sequential.
Dave
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