[R] eval and as.name

[Fuchs Ira]

I'm sure there is a more general way to ask this question but how do  
you use the elements of a character vector as names of objects in an  
expression?
For example, say you have:

a = c(1,3,5,7)
b = c(2,4,6,8)

n=c("a","b")

and you want to use the names a and b in a function (e.g. sum)

sum(eval(as.name(n[1])),eval(as.name(n[2])))

works but

what is a simpler way to effect this level of indirection?