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From: VK on 27 Jun 2010 08:19
On Jun 27, 2:10 am, Stefan Weiss <krewech...(a)gmail.com> wrote:
> I retract that. Do _not_ look at the SpiderMonkey parser/interpreter
> code unless you're drunk or a wizard (or both).

Even that can be not enough for core stuff like that :-) A drunk
smoking grass wizard would be comfortable I guess :-) To be fair, it
is not Gecko only problem: any old enough system if ever studied
internally will kill anyone's programming illusions once and forever.
My personal hint: do *not* study Java core (anything below Swing) :-)

> I found an older version
> lying around in my ~/build directory and got curious. Now I've got a
> headache.
>
> To make it short: after peeling away the onion-like layers of macros and
> arcane typedefs that make up the JavaScript interpreter, and wrapping my
> head around stuff like the difference between JS_ValueToBoolean and
> js_ValueToBoolean, what it comes down to is this:
>
> src/jsinterp.c
>    ...
>    BEGIN_CASE(JSOP_NOT)
>       POP_BOOLEAN(cx, rval, cond);
>       PUSH_OPND(BOOLEAN_TO_JSVAL(!cond));
>    END_CASE(JSOP_NOT)
>    ...
>    #define POP_BOOLEAN(cx, v, b)
>       ...
>       ok = js_ValueToBoolean(cx, v, &b);   // [ed] branch for strings
>
> src/jsbool.c
>    ...
>    js_ValueToBoolean(JSContext *cx, jsval v, JSBool *bp)
>    {
>      ...
>      } else if (JSVAL_IS_STRING(v)) {
>          b = JSSTRING_LENGTH(JSVAL_TO_STRING(v)) ? JS_TRUE : JS_FALSE;
>      ...
>      }
>      *bp = b;
>
> The length of a string operand for JSOP_NOT (a.k.a. "!") is used to
> decide whether the expression evaluates to true or false. There's no
> creation of new Boolean objects anywhere. BOOLEAN_TO_JSVAL doesn't
> create any, and JS_TRUE and JS_FALSE are (indirectly) defined as 1 and
> 0, respectively.

Shall we declare now that JavaScript doesn't have true and false
values as well? :-) I can tell you right away that JavaScript doesn't
have any objects: on C level these are strings and number
manipulations as well and nothing else. And C itself does not have any
subroutines, identifiers and stuff: in the reality these are just
processor instructions and nothing else.

Talking about language - is not talking about the engine.

I am still collecting data at my spare time. I'll be back :-)



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