Accumulator Generator with R
Paul Graham ( http://www.paulgraham.com/accgen.html ) gives the following problem:
Write a function foo that takes a number n and returns a function that takes a number i, and returns n incremented by i.
In R, we could write it like this:
foo <- function (n) function (i) (n <<- n + i)
We can create a new function fun …
fun <- foo(2.43)
fun
function (i) (n <<- n + i) <environment: 0x3831bc8>
… and test it.
fun(1.1) fun(1.1) fun(2.1)
[1] 3.53 [1] 4.63 [1] 6.73
Without the parentheses around n <<- n + i, the new function would
return n invisibly. So it would still work, but we would need to
call print explicitly.
foo <- function (n) function (i) n <<- n + i fun <- foo(1.1) fun
function (i) n <<- n + i <environment: 0x3aad238>
fun(2.1) print(fun(3.1)) ## 1.1 + 2.1 + 3.1
[1] 6.3