Lists are the central datatype in applicative programming. In imperative programming the array is the central datatype. Arrays are provided in a type-safe way in Standard ML through the use of the following operations of the Array structure in the Standard ML library.

- the type 'a Array.array;
- the creation functions Array.array of type (int
* 'a) ->
'a Array.array and

Array.fromList of type 'a list -> 'a Array.array; - the Array.update operation of type ('a Array.array * int * 'a) -> unit; and
- the operation Array.sub with type ('a Array.array * int) -> 'a with exception Subscript. Subscripting begins from 0.

vala = Array.fromList [1];valb = Array.fromList [1];

then a and b are *not* equal.