Specifications

199
Description:
■ Creating a user-defined function
DEF FN...END DEF creates a user-defined function. The function definition block
between
DEF FN and END DEF is a set of some statements and functions.
• Definition of a user-defined function should appear preceding a calling statement
of the user-defined function in a source program.
• You cannot make double definition to a same function name.
• This statement block should not be defined in the block-structured statements
(
DEF FN...END DEF, FOR...NEXT, FUNCTION...END FUNCTION, IF...THEN...
ELSE...END
IF, SELECT...CASE...END SELECT, SUB...END SUB and WHILE
...WEND
), in the error-handling routine, event-handling routine, or in the subrou-
tines.
•
DEF FN...END DEF functions can be recursive.
• In defining a string function, you can specify the maximum
stringlength. If
its specification is omitted, the default value of 40 characters takes effect.
•
dummyparameter, which corresponds to the variable having the same name in
the function definition block, is a local variable valid only in that block. Therefore,
if a variable having the same name as
dummyparameter is used outside DEF
FN...END
DEF statement block or used as a dummyparameter of any other
function in the same program, then it will be independently treated.
• In user-defined functions, you can call other user-defined functions. You can nest
DEF FN...END DEF statements to a maximum of 10 levels.
• When using the
DEF FN...END DEF together with block-structured statements
(DEF FN...END DEF, FOR...NEXT, FUNCTION...END FUNCTION, IF...THEN...
ELSE...END
IF, SELECT...CASE...END SELECT, SUB...END SUB and WHILE
...WEND
), you can nest them to a maximum of 30 levels.
• If variables other than
dummyparameter(s) are specified in the function defini-
tion block, they will be treated as global variables whose current values are avail-
able.
•
EXIT DEF exits the function block prematurely and returns control to the position
immediately after the statement that called the user-defined function.
• The block-format
DEF FN statement should be followed by END DEF which ends
the function block and returns control to the position immediately after the state-
ment that called the user-defined function.
• Using Syntax 5 allows you to assign a return value for a user-defined function.
The type of
functionname should match that of a return value. If no return
value is assigned to
functionname, then the value 0 or a null string will be
returned for a numeric function or a string function, respectively.