Here it is in Perl6:

  [+] ^6

Actually cheated slightly because ^6 creates list from 0..5 :)

So correct match would be...

  [+] 1..5

Here's how you would do it in Io:

  list(1, 2, 3, 4, 5) reduce(+)

In Rebol there isn't a functional fold/reduce built in. So one way to do the one-liner would be:

  x: [1 2 3 4 5] forskip x 2 [insert x '+] x: do next x

Above changes x to 15. Alternatively approach which doesn't clobber x:

  x: [1 2 3 4 5] y: [] forall x [repend y [x/1 '+]] take/last y do y

I'm sure someone with more Rebol chops can see other (better!) ways of doing this :)