APL Dynamic Scope
APL uses dynamic scoping, that is arguments and local variables defined in the stack of callees are visible to the caller function, as long as they are not redefined.
A characteristic language with dynamic scoping is LISP.
OUTER 123 IN OUTER X=123 ONE=11 TWO=22 IN INNER X=456 ONE=12 TWO=22
J Static Scope
In J local names are only visible in the current (explicit) definition.
outer=: 3 : 0 one=. 11 two=. 22 q=. 'in outer y=',(":y) q=. q,' one=',(":one),' two=',":two smoutput q inner 456 ) inner=: 3 : 0 one=. 12 q=. 'in inner y=',(":y) q=. q,' one=',(":one),' two=',":two smoutput q )
Though global names are visible in any scope.
outer 123 in outer y=123 one=11 two=22 |syntax error: inner | q=.q ,' one=',(":one),' two=',":two two=. 20 outer 123 in outer y=123 one=11 two=22 in inner y=456 one=12 two=20
- Scope (programming), Wikipedia
- [http:?action=fullsearch&value=closure Closure Topics], J Wiki
Contributed by Oleg Kobchenko