Checking for equality in lists in SML

Question

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 :)

What do you mean by "writing down the whole thing"? Writing equal (list01, list09) is actually longer than writing list01 = list09, so what's the "whole thing" you want to avoid writing? — sepp2k
i assumed it would be easier to create a function compare ([list01,list09]); than actually compare the two lists manually, if they were very! long. — user457142

wojtek wojtek · Accepted Answer · 2010-09-29T09:37:18

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

Checking for equality in lists in SML

2 Answers