No, you’d just memoise it to a variable:
a?.d().f?.b
to:
var _temp, _temp2;
(a != undefined ? (temp = a.d() != undefined ? (_temp2 = _temp.f != undefined
? _temp2.b : undefined) : undefined)));
You’re going to need to memoise all member expressions anyway as they might be
accessing a getter and you don’t want to call it twice.
On Tue, Apr 7, 2015 at 7:32 PM, joe <[email protected]> wrote:
> Okay. I've updated my transpiler to demonstrate how (and why) this could
> work at the VM level (I do think VM devs will have to add new opcodes for
> this), and I've appended an example transformation to this email.
> Why is this so complicationed? The answer is that when you start nesting
> ?. operators, it's pretty easy to cause some operators to be called twice.
> E.g, if you transformed the following to the NULL syntax:
> a?.d().f?.b
> You would get:
> (a != undefined ? (a.d() != undefined ? (a.d().f != undefined ? a.d().f.b
> : undefined) : undefined)));
> Notice how a.d() gets called multiple times.
> The solution is probably new VM opcodes. Since my transpiler is obviously
> not a VM, it transforms ?. operators into auto-generated functions.
> Anyway, here's the example I transpiler:
> a?.b.c.e?.f.g?.h.t.c?.d()?.e;
> Which turned into this:
> function q0eILlfx7_3(obj) {
> var _t=obj;
> if (_t==undefined)
> return undefined;
> _t = _t.b.c.e;
> if (_t==undefined)
> return undefined;
> _t = _t.f.g;
> if (_t==undefined)
> return undefined;
> _t = _t.h.t.c;
> if (_t==undefined)
> return undefined;
> _t = _t.d();
> return _t;
> }
> q0eILlfx7_3(a);
> On Tue, Apr 7, 2015 at 6:24 PM, Brendan Eich <[email protected]> wrote:
>> joe wrote:
>>
>>> That's a good point. Are lexical non-DFA grammars allowed? It would be
>>> trivial to solve that with a regular expression lookahead. Although I
>>> suppose at that point you might as well call it a cover grammar.
>>>
>>
>> We must avoid being too clever -- it complicates implementations and
>> inevitably incurs future-hostility to extensions we may want, if not
>> outright bugginess.
>>
>> All of this suggests prefix ? is the better course. Anyone have
>> counterexamples?
>>
>> /be
>>
>>>
>>> Joe
>>>
>>> On Mon, Apr 6, 2015 at 2:42 PM, Brendan Eich <[email protected]
>>> <mailto:[email protected]>> wrote:
>>>
>>> joe wrote:
>>>
>>> By the way, I don't remember having grammar issues (I use a
>>> LALR compiler-compiler). Looking at my code, it looked like I
>>> handled it in the tokenizer stage; I added a COND_DOT token:
>>>
>>> COND_DOT : \?\.
>>>
>>>
>>> Did you keep backward compatibility? `x?.1:y` must continue to work.
>>>
>>> /be
>>>
>>>
>>> No, it looks like I didn't.
>>>
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