SIMPOL Documentation

SIMPOL is what is known as a strongly typed language. By this is generally meant that it is considered an error to assign an object or value of one type to a variable of another type. As an example, if I have one variable that is declared to be of type integer it is an error to assign a variable of type number to that variable. It will result in a type mismatch error. This is one way that the programming language protects the programmer from making an error that might otherwise be very hard to find. If instead of generating an error, the programming language automatically converted the variable of type number to an integer value, truncating or rounding the non-integer portion of the value, it would be very difficult to track down, especially in a large program since the problem may only appear to be intermittent (it would only occur when the value in the variable of type number was not an integer value).

That is all well and good, but there are some situations where it is absolutely essential to be able to handle more than one type using only one variable. As an example, consider the situation where you may wish to process all of the controls on a form. Each form control has its own type. If it is possible to declare a variable to be of type FormControl and if that type is designed to represent any form control, then it would then be possible to use a single variable to contain a reference to any control on the form, without causing an error. In SIMPOL by using the type property of the object it would then be possible to detect which type the variable currently contains and to perform appropriate operations on that object. Later in this chapter this capability, also known as polymorphism, is discussed in greater detail.