Here's my algorithm, the languague is sml

fun last(1st) (x::b) =

if null x then nil

else b;

I keep getting this error:

stdIn:1.11 Error: non-constructor applied to argument in pattern.

if someone could point in the right direction, once I figure this out I should be able to finish the rest of the lab. Thank you in advance :)

A function last (1st) of type 'a list -> 'a which returns the last element of a given list