[parenscript-devel] BLOCK/RETURN-FROM

[Vladimir Sedach]

This approach should be working in some code I just pushed
(ae093417db848a1). I'm not checking whether return-from is executed,
but rather taking the intersection of named blocks that can only be
reached dynamically with the return-from tags that are contained
lexically in those blocks, and generating the wrapping try-catch in
the corresponding block places based on that.

Happy hacking,
Vladimir

On Tue, Jun 7, 2011 at 2:07 PM, Red Daly <reddaly at gmail.com> wrote:
> At one point I had this implemented using try-catch unless Parenscript's
> compiler could prove (rather naively) that the return-from clause was always
> executed.  I am usually way behind the official branch, and I'm not sure if
> my changes ever made it in, and if they did if this case is a bug.  Anyway
> it would do something like
>
> function foo() {
>    try {
>
>    var bar = function () {
>        throw { 'ps-return-foo341' : 42 };
>    };
>     bar(); }
>    catch (e) {
>       if ('ps-return-foo341' in e)
>          return e['ps-return-foo341'];
>       else
>            throw e;
> };
>
> verbose, but it should always work.  other try-catch tricks allow lisp-style
> conditions, which I detailed in a post in this list within the year.  in
> case of group interest the relevant code is available
> at https://github.com/gonzojive/paren-psos
> and https://github.com/gonzojive/parenscript
>
> Viva Parenscript!
>
> Red
>
>
> On Tue, Jun 7, 2011 at 11:40 PM, <sblist at me.com> wrote:
>>
>> Hi,
>>
>> I was wondering if the BLOCK/RETURN-FROM feature in PS intends
>> to support the following case:
>>
>> (ps (defun foo ()
>>          (flet ((bar () (return-from foo 42)))
>>            (bar))))
>>
>> =>
>>
>> WARNING: Returning from unknown block FOO
>> "function foo() {
>>    var bar = function () {
>>        return 42;
>>    };
>>    return bar();
>> };"
>>
>> In order to try and get around the warning, I tried this:
>>
>> (ps (defun baz ()
>>          (block foo
>>            (flet ((bar () (return-from foo 42)))
>>              (bar)))))
>>
>> =>
>>
>> WARNING: Returning from unknown block FOO
>> "function baz() {
>>    var bar = function () {
>>        return 42;
>>    };
>>    return bar();
>> };"
>>
>> but that didn't seem to work. Any ideas on how to achieve lexical
>> return here?
>>
>>        - Scott
>>
>>
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>
>
>
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