Does using closures in sml affect the speed of running code in the interactive compiler?

Question

If I have a program say:

fun foo x =
    let
       fun bar y = y * y
    in
       x + (bar x)
    end

    foo 123;

When I run this program in SML/NJ without compiling, will it have to process the declaration of bar each time foo is called? As it would in an interpreted language.

Will it run slower than

fun bar y = y * y
fun foo x = x + (bar x)
foo 123;

Since value bindings get updated when each time you call a function this question has been brought to my mind.
Or will SML solve this in some neat way under the hood?

Answer 1

SML/NJ in interactive mode still compiles your functions to native code. By the time you've declared foo, your intermediate variables have probably been optimised away. i.e. Chances are it will compile down to the same as something like val foo = fn x => x + (x * x), and without the overhead of a second function, it should be faster if anything.