MAKE THIS SML CODE OUTPUT "[1,2,3]"

fun merge([], ys) = ys
| merge(xs, []) = xs
| merge(x::xs, y::ys) =
if x < y then x::merge(xs, y::ys)
else y::merge(x::xs, ys)

fun split [] = ([],[])
| split [a] = ([a],[])
| split (a::b::cs) =
let val (M,N) = split cs in
(a::M, b::N)
end

fun mergesort [] = []
| mergesort [a] = [a]
| mergesort [a,b] = if a <= b then [a,b] else [b,a]
| mergesort L =
let val (M,N) = split L
in
merge (mergesort M, mergesort N)
end