B.3 Primitive Types

ML has the following primitive types: integer (int), real (real), boolean (bool), character (char), and string (string):

Notice that ML uses type inference. The : colon symbol associates a value with a type and is read as “is of type.” For instance, the expression 3 : int indicates that 3 is of type int. This explains the responses of the interpreter on lines 2, 4, 6, 8, and 10 when an expression is entered on the preceding line.