Hi all, For a while now Factor has required that the stack effect be declared on recursive words. Non-recursive words did not require a declaration, but it was considered good style to add one except for the most trivial words (such as those pushing constants on the stack).
Well, the problem is that I recently realized any word can technically become recursive, _except_ those that push constants on the stack! So what we have now is unsound. Consider this scenario: You're working at a large enterprisey firm on a project with lots of developers ;-) Developer A writes the following code: GENERIC: a ( x -- y ) GENERIC: c ( x -- y ) Developer B writes the following code: : b ... a ... ; ! no stack effect declaration -- but it's not recursive! M: foo c ... b ... ; Developer C writes this: M: bar a ... c ... ; Wham, suddenly 'b' is recursive, because we have a cycle in the control flow graph: a -> c -> b -> a, which didn't exist before! But developer C doesn't care about the word 'b', they may not know it exists even, but they just broke it. This scenario is not contrieved; it comes up in extra/ from time to time. Someone will add some code which defines a bunch of methods, then suddenly the compiler starts complaining about some totally random word being recursive and needing a stack effect, such as this word from calendar.format: : YYYY year>> write-0000 ; Surely it doesn't look recursive, but there is some path through the call graph where write-0000 calls write, which calls some low-level Unix I/O code, which somehow calls back into the calendar code... To make matters worse, it doesn't _always_ complain about a word needing a stack effect declaration. Sometimes things work out just fine and it gets along without hitting the code path where it needs the declaration to be there. So what we have here is that some guy makes an innocent-looking change to the code, and at some undetermined point in the future, a totally unrelated word may stop compiling. The technical term for languages with such features is "toy language" :-) Since my plan is to use Factor to take over the world and get disgustingly rich, this is not an acceptable state of affairs. There are two solutions: 1) Revive the old stack effect inference algorithm which did not require annotations at all. 2) Require stack effect declarations on all words except for the most trivial ones which only push literals on the stack I don't want to do #1 because the old algorithm was more complex, both in terms of code and run time. So that leaves us with #2. I don't mind having to annotate more words, what do you guys think? Slava ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
