Ah yes clearer. This is similar to Vladimir's case from upthread:
(defun foo () (blah) (some-random-js-function))
... except that my suggestion that the compiler figure out when BLAH isn't in a return position and do something like:
function foo() { blah(); RETURN_VALUES = null; return someRandomJsFunction(); };
... won't work in your case, i.e. when FOO is not a PS function.
But I wonder whether perfect interop from JS back into PS isn't an overly ambitious a thing to promise. When language A and language B have different calling conventions and you call B from A, it's normal to have to follow some protocol to manually bridge the gap between them. In this case the protocol might be: you must either return the call to BLAH or clear RETURN_VALUES. Yeah this would be a pain and easy to forget, but it is arguably a reasonable card for PS to have to play here.
That being said, it's not surprising that a simple global variable wouldn't do the trick in every case. I hope we can come up with something that does.
But let's not forget that the current implementation is even more broken. It doesn't do the right thing even if BLAH is in a return position - so *none* of the cases we're talking about actually work right now.
Daniel
On Wed, Aug 29, 2012 at 10:16 AM, Red Daly reddaly@gmail.com wrote:
Hi Daniel,
I'm glad to be part of the discussion :) On Aug 28, 2012 8:53 PM, "Daniel Gackle" danielgackle@gmail.com wrote:
Hi Red,
I was hoping you'd chime in. I'll see your scenario 3 and raise you a 3a and a 3b:
Scenario 3a: A non-Parenscript function that calls a mv-returning Parenscript function but only needs its first return value;
Scenario 3b: A non-Parenscript function that calls a mv-returning Parenscript function and needs all its return values.
3a works fine as long as the MV implementation is careful to use a normal JS return to pass the first return value back to the caller. That's true both of what PS does today and of the global-var proposal.
As for 3b (the scenario, not the hacker!), seems to me this can't work at all and there's no need to support it. If you're a non-PS function then by definition you can't use PS's MULTIPLE-VALUE-BIND to access the additional return values because the MV construct only exists in PS. I suppose if you really wanted to you could manually write JS to do whatever PS does to supply those values to the caller, but then you're not really a non-PS function anymore, so much as a manually-compiled PS function.
Daniel
I wasn't clear in my original post. I'm not concerned with the non-Parenscript function's ability to receive multiple values. I'm concerned that the non-Parenscript function will interfere with the multiple value return.
If a non-Parenscript function calls a Parenscript function that messes with the global variables, the non-Parenscript function could end up returning stuff unintentionally. This is because the non-Parenscript function will not manipulate the global variables to clean up the unused multiple values that are returned.
Here's some code to illustrait the point:
(defun ps-foo () (multiple-value-bind (a b) (bar) (+ a b)))
(defun ps-fn-returns-mv () (values 1 2))
function barWorks() { return psFnReturnsMv(); }
function barBreaks() { psFnReturnsMv(); // global variables for MV returning get set up and linger // return a single value: 42 return 42; }
Let's assume the two Parenscript functions translate into something like this:
var RETURN_VALUES = null; var MV_CALL = false; ... other global variables related to multiple values
function psFoo() { // global variable stuff MV_CALL = true; RETURN_VALUES = null;
var a = bar(); MV_CALL = false; var b = RETURN_VALUES ? RETURN_VALUES[0] : undefined; return a + b; }
function psFnReturnsMv() { if (MV_CALL) RETURN_VALUES = [ 2 ]; return 1; }
When bar = barWorks, foo will return 1 + 2, as intended. When bar = barBreaks, foo will incorrectly return 42 + 2 because the global variables were not properly cleaned up.
I hope this makes sense.
- Red