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 Defines and names a function.
 
 Syntax 1:
    DEF FNname[(parameterlist)] = expression
 
 Syntax 2:
    DEF FNname[(parameterlist)]
         [statementblock]
    FNname = expression
         [statementblock]
         [EXIT DEF]
         [statementblock]
    END DEF
 
    ■ parameterlist    One or more arguments in the following form:
 
      [BYVAL] variable[( )] [AS type] [, [BYVAL] variable[( )] [AS type]]...
 
                       • BYVAL     Indicates the parameter is passed by value
                                   rather than by reference; cannot be used
                                   with a variable of a user-defined type
 
                       • variable  Visual Basic variable name; for array
                                   variables, empty parentheses are required
 
                       • type      Data type of the variable: INTEGER, LONG,
                                   SINGLE, DOUBLE, STRING, or a user-defined
                                   data type
 
    ■ expression       Return value of the function
 
    ■ EXIT DEF         Immediately exits an executing DEF FN function
 
 See Also
    ◄DEF FN Scope Rules►               ◄DEF SEG Statement►
    ◄FUNCTION Statement►               ◄SHARED Statement►
    ◄STATIC Statement►