According to http://cran.r-project.org/doc/contrib/Fox-Companion/appendix-scope.pdf and other examples online, I am to believe that R resolves variables using lexical scoping by following the frames up the call stack.  However, that's not working for me.  For example, the following code, taken from the reference above fails instead of returning 7.  What am I doing wrong?  Thanks!

f <- function(x) { a<-5; g(x) }
g <- function(y) { y + a }
f(2)
Error in g(x) : object 'a' not found


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