The type of data presented to a function must correspond to the operations to be performed on the data. This can be accomplished in several ways:
Programmer Type Checking: It is the programmer's responsibility to insure that a call to a function is made with the proper data types. (e.g., Fortran.)
Static Type Checking: The compiler must be able to know at compile time what the type of each data item is. (e.g., Pascal, Ada.)
Dynamic Type Checking: The type of each piece of runtime data can be determined. The application program tests the type of the data before performing operations on it. (e.g., Lisp.)