r - When is Lexical Scope for a function within a function determined? -


i've looked @ other lexical scoping questions in r , can't find answer. consider code:

f <- function(x) {   g <- function(y) {     y + z   }   z <- 4   x + g(x) } f(3)

f(3) return answer of 10. question why? @ point g() defined in code, z has not been assigned value. @ point closure g() created? "look ahead" rest of function body? created when g(x) evaluated? if so, why?

when f run, first thing happens function g created in f's local environment. next, variable z created assignment.

finally, x added result of g(x) , returned. @ point g(x) called, x = 3 , g exists in f's local environment. when free variable z encountered while executing g(x), r looks in next environment up, calling environment, f's local environment. finds z there , proceeds, returning 7. adds x 3.

(since answer attracting more attention, should add language bit loose when talking x "equals" @ various points not accurately reflect r's delayed evaluation of arguments. x will be equal 3 once value needed.)


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