Re: [Factor-talk] What exactly is the retain stack?
2014-05-16 0:29 GMT+02:00 Jon Purdy evincarofaut...@gmail.com: Is that it's only use? Then why? dip can easily be formulated using non-retain stack using primitives: For example: a b c [ append ] dip - a b c -rot append swap That implementation assumes the quotation takes two operands and produces one result, which is not always the case. More generally, the functional argument of “dip” is not really supposed to be able to touch the argument it’s operating under. If you don’t have types or a stack checker enforcing this, the formulations with a retain stack or dynamically composing quotations are safe by construction, but the “-rot” version is not. Consider “[ 3drop ] dip” or “[ append dup ] dip”. But factor *does* have a stack checker. Since the stack effect of the quotation given to dip can be inferred, you can always (I think?) rewrite them using nothing but normal stack shuffling operations. Like so: : make-shuffle-effect ( n dir -- effect ) swap 1 + iota swap dupd rotated [ array ] bi@ effect ; : emit-dip ( quot -- ) dup infer [ nip in length -1 make-shuffle-effect , \ shuffle-effect , ] [ swap , , \ call-effect , ] [ nip out length 1 make-shuffle-effect , \ shuffle-effect , ] 2tri ; : rewrite-dip ( quot -- quot' ) first2 drop [ emit-dip ] [ ] make ; [ [ append over ] dip ] rewrite-dip will output the quotation: [ ( 0 1 2 3 -- 3 0 1 2 ) shuffle-effect [ append over ] ( x x x -- x x x ) call-effect ( 0 1 2 3 -- 1 2 3 0 ) shuffle-effect ] Now neither shuffle-effect nor call-effect are Factor primitives but they easily could have been and then dip would only need to touch the data stack. -- mvh/best regards Björn Lindqvist -- Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free. http://p.sf.net/sfu/SauceLabs ___ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
Re: [Factor-talk] What exactly is the retain stack?
Björn Lindqvist bjou...@gmail.com writes: Hi! Is that it's only use? Then why? dip can easily be formulated using non-retain stack using primitives: For example: a b c [ append ] dip - a b c -rot append swap What if the contents of the quotation use more than one item from the stack? How would you implement [ + ] dip, for example? Or [ + + ] dip? etc. etc. Rupert pgpDjqZUFweIY.pgp Description: PGP signature -- Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free. http://p.sf.net/sfu/SauceLabs___ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
Re: [Factor-talk] What exactly is the retain stack?
On Fri, May 16, 2014 at 7:38 AM, Björn Lindqvist bjou...@gmail.com wrote: 2014-05-16 0:29 GMT+02:00 Jon Purdy evincarofaut...@gmail.com: Is that it's only use? Then why? dip can easily be formulated using non-retain stack using primitives: For example: a b c [ append ] dip - a b c -rot append swap That implementation assumes the quotation takes two operands and produces one result, which is not always the case. More generally, the functional argument of “dip” is not really supposed to be able to touch the argument it’s operating under. If you don’t have types or a stack checker enforcing this, the formulations with a retain stack or dynamically composing quotations are safe by construction, but the “-rot” version is not. Consider “[ 3drop ] dip” or “[ append dup ] dip”. But factor *does* have a stack checker. Since the stack effect of the quotation given to dip can be inferred, you can always (I think?) rewrite them using nothing but normal stack shuffling operations. Like so: : make-shuffle-effect ( n dir -- effect ) swap 1 + iota swap dupd rotated [ array ] bi@ effect ; : emit-dip ( quot -- ) dup infer [ nip in length -1 make-shuffle-effect , \ shuffle-effect , ] [ swap , , \ call-effect , ] [ nip out length 1 make-shuffle-effect , \ shuffle-effect , ] 2tri ; : rewrite-dip ( quot -- quot' ) first2 drop [ emit-dip ] [ ] make ; [ [ append over ] dip ] rewrite-dip will output the quotation: [ ( 0 1 2 3 -- 3 0 1 2 ) shuffle-effect [ append over ] ( x x x -- x x x ) call-effect ( 0 1 2 3 -- 1 2 3 0 ) shuffle-effect ] Now neither shuffle-effect nor call-effect are Factor primitives but they easily could have been and then dip would only need to touch the data stack. There are still escape hatches from the static checker, like 'with-datastack', 'clear', 'execute( -- )', etc., and before the compiler comes online, the VM JIT uses a dynamic stack model. The retain stack could however be folded into the callstack, as is traditionally done in Forth, since even the dynamic stack model relies on retain stack balance being preserved. That's one of those little optimizations we never got around to doing. -Joe -- Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free. http://p.sf.net/sfu/SauceLabs___ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
