On Tuesday, March 24, 2015 at 7:21:32 AM UTC-4, Thomas Heller wrote:
> >
> > Question: why exactly is this type hint needed when js/goog.DEBUG is used
> > in an "if"? As far as I can see, js/goog.DEBUG is a boolean already.
> >
>
> Short answer: We don't evaluate or parse any Javascript when compiling
> ClojureScript. That means we don't know about goog.DEBUG and what type it may
> be. CLJS is parsed and analyzed so we know a whole lot about it without
> actually running anything.
I was curious and used the cljs compiler from [1] and compiled the code of the
type annotated vs the non-type annotated. Using :advanced to compile this:
(if js/goog.DEBUG (println "(if goog.DEBUG...")) ;; no type hint
(if-not js/goog.DEBUG (println "(if-not goog.DEBUG...")) ;; no type hint
(when-debug (println "when-debug")) ;; when-debug from David
inspect the output you can see this output:
[... omitted ...]
$cljs$core$truth_$$(!1) && console.log("(if goog.DEBUG...");
!$cljs$core$truth_$$(!1) && console.log("(if-not goog.DEBUG...");
where the (when-debug ..) call is missing (as it should be). However the other
two check cljs.core.truth_ for truthiness. Now the interesting part: Pasting
the following code:
function $cljs$core$truth_$$($x$$54$$) {
return null != $x$$54$$ && !1 !== $x$$54$$;
}
function $cljs$core$not$$($x$$58$$) {
return $cljs$core$truth_$$($x$$58$$) ? !1 : !0;
}
$cljs$core$truth_$$(!1) && console.log("(if goog.DEBUG...");
!$cljs$core$truth_$$(!1) && console.log("(if-not goog.DEBUG...");
// Sometime also produces:
$cljs$core$not$$(!1) && console.log("(if-not goog.DEBUG...");
into:
https://closure-compiler.appspot.com/home
with advanced compilation will actually get rid of the truth_ call and elide
it. HOWEVER, pasting the _entire_ javascript output produced by the cljs
compiler into the same window (appspot) and the call remains in place. So does
that mean there is potential to improve the google closure compiler? Or does it
mean that there is other produced code by cljs that prevents this inlining to
happen?
[1]
http://swannodette.github.io/2015/03/16/optimizing-clojurescript-function-invocation/
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