Why R code with `{}` is faster than that with `()`?

Question

Why is the R code with {} in general faster than the one with (), example below ?

n=10000000
w1=numeric(n)
w2=numeric(n)
r=rnorm(n)


t1=Sys.time()
for(i in 1:n)
w1[i]=((r[i]^2))*(1*1)
t1-Sys.time()


t1=Sys.time()
for(i in 1:n)
w2[i]={{r[i]^2}}*{1*1}
t1-Sys.time()

Answer 1

baptiste already linked Radford Neal's blog in the comments.
But since the SE people don't like links to external sites, let me quote an interesting comment of the author himself (comment 33):

Yes, parentheses are still slower than curly brackets in R 2.13.1, and in the latest R 2.14.1, though not by as much as before (a patch I suggested to reduce general overhead in built-in functions was incorported in later releases, which reduced this difference).

There’s no good reason for parentheses to be slower. I suggested another change (to just a couple lines of code) that would speed up parentheses. Luke Tierney responded that this patch should on no account be incorporated into R, on the basis that parentheses are an operator just like sqrt, and that there should therefore be nothing in the code implementing parentheses that departs from how operators like sqrt are implemented.

Knowing that, ( ) appears to be an operator - much like a function doing basically nothing -
while { } is a language construct.
The parentheses ( ) incorporate some overhead code common to all operators which is actually of no need for them.