Standard ML Standard ML is one of the best-developed examples of a functional language. Pairs and Tuples SML has a built-in type of pairs. You can pair to- gether any two values. Lists SML also has a built-in data type of lists, i.e., sequences of zero or more values. You can make lists of anything, but everything in a given list must have the same type.
Lists have two interchangeable representations.
The other way to write a list is to write the elements within square brackets, separated by commas, as illustrated in the values echoed by the interactive system.