Defines a function.
 
DEF FNname[(parameterlist)] = expression
DEF FNname[(parameterlist)]
    [statementblock]
  FNname = expression
    [statementblock]
  EXIT DEF]
    [statementblock]
  END DEF
 
    - parameterlist    One or more arguments in the following form:
 
                       variable[( )] [AS type] [, variable[( )] [AS type]]...
 
                       variable    A Basic variable name.
                       type        The data type of the variable (INTEGER,
                                   LONG, SINGLE, DOUBLE, STRING, or a
                                   user-defined data type).
 
    - expression       The return value of the function.
 
    - The FUNCTION statement provides a better way to define a function.
 
See Also    <EXIT>    <FUNCTION>    <SHARED, STATIC>