R does have call-by-need semantics, like (an impure) Haskell, but that's not why replicate's second argument gets evaluated multiple times: replicate <- func

R does have call-by-need semantics, like (an impure) Haskell, but that's not why replicate's second argument gets evaluated multiple times: replicate <- function (n, expr, simplify = TRUE) sapply(integer(n), eval.parent( substitute(function(...) expr)), simplify = simplify) The replicate function uses R's compute-on-the-language to construct a new function that has expr as its body. A closure's argument will be evaluated at most once.