Hello, In Scheme:
(define a 10) (list a) => (10) (let ((a 20)) (list a)) => (20) (let ((a 30)) (set! a 40) (list a)) => (40) ; The a established by the (a 30) inside the let is set. (list a) => 10 ; The top-level a is still 10 (let () (set! a 50)) (list a) => (50) ; Even though we ran set! inside a new scope, the top-level a was changed. This is because there is no new a binding in the let to shadow the top-level a. SYMBOL: a 10 a set [ 20 a set a get ] with-scope => 20 a get => 10 This is not like Scheme. a is set inside the scope but it doesn't affect the top-level a. There isn't a let binding to shadow the top-level. This behaviour is a result of the set word which *always* modifies the top of the namestack. So let's make set* which searches up the namestack until it find the variable and modifies it there. ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! USING: kernel kernel-internals sequences hashtables ; : set-hash-stack ( value key seq -- ) dupd [ hash-member? ] find-last-with nip set-hash ; : set* ( val var -- ) namestack* set-hash-stack ; ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 10 a set [ 20 a set* a get ] with-scope => 20 a get => 20 ! set* modified the a variable in the namespace one level up. Factor beginners, if you feel lost, it's probably because you haven't explored the namestack, what it is, where it is, how things modify it. Read the "Variables and Namespaces" section of the manual and experiment with the namestack*, set, get, >n, ndrop words. Then see how with-scope is defined in terms of >n and ndrop. Finally, come back and understand set-hash-stack and set*. Ed ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
