Expressions are constructs made up of operators and operands.
Expressions work with existing data and return new data. In TMT Pascal there
exist two types of operations, unary and binary. Unary operations work with
one operand and binary operations work with two operands. Regardless of the
operator, operands may be constants, variables, data returned by another
operator, or data returned by a function call. Operators can be grouped
according to the types they operate on. There are five groups of operators:
integer, real, Boolean, set, and relational.