Checking for equality in lists in SML

Question

Hi there, i want to write a function that checks for equality of lists in SML for instance : [1,2,3]=[1,2,3]; val it = true : bool

So instead of writing down the whole thing, i want to make a function that takes two predefined lists, and compare them, so that if list01 = [1,2,3] and list09 = [1,2,3] then fun equal (list01,list09); will return -val it = true : bool;

Thanx in advance for any ideas/hints and help :)

Answer 1

Here is a not checked sample:

fun compare ([], []) = true # both empty
    |   compare (x::xs, y::ys) = (x = y) and compare(xs,ys)
    |   compare (_, _) = false # different lengths

Answer 2

You seem to be aware that = works on lists, so (as I already said in my comment) I don't see why you need to define an equal function.

That being said, you can just write:

fun equal (a, b) = (a = b);