Subroutines

Subroutines are first class citizens in ScriptBasic for Java. You can write subroutines in your BASIC program and call them from the main part of the BASIC program, or from another subroutine or from the same subroutine recursively.

ScriptBasic for Java subroutines can have return values. There is no syntactic difference between subroutines and functions, procedures or anything else. There is subroutine only, that may return some value at its will. To return a value the statement RETURN is to be used. The format of a subroutine is:

SUB mySubroutine [ ( arguments ) ]

 commands
 [ RETURN expression ]

ENDSUB

A subroutine starts with the keyword SUB and should have a unique name. You can not have two subroutines having the same name in a BASIC program. A subroutine can have arguments, but they are optional. If the subroutine does not have arguments, then you can optionally leave the parentheses off and you can simply write

SUB mySubroutine
 commands
ENDSUB

or you can write, just as well

SUB mySubroutine()
 commands
ENDSUB

Both approaches are equally good. However when you use a subroutine in an expression you can not omit the opening and closing parentheses. If you do so, the interpreter will treat the identifier as an undeclared variable and will not call the subroutine. Instead you will probably get undef value. It is generally bad practice to use the same identifier to name a subroutine and a variable, but ScriptBasic for Java does not prevent you.

If you have arguments they behave like local variables. If there are arguments for your subroutine you have to provide those values when you call the subroutine. You have to provide exactly that many arguments as many the subroutine expects otherwise you will receive runtime error. (Note that later versions will check this during compile time.)

To invoke a subroutine you can use the name of the subroutine in an expression followed by ( and ) and an expression list between the parentheses, like

a = 1 + mySubroutine(13,"apple","pie")

If your subroutine does not return any value then the special value undef will be used as return value. If your subroutine is more a real subroutine than a function call you can call it using the keyword CALL:

CALL mySubroutine(13,"apple","pie")

ScriptBasic for Java is quite liberal with the keyword CALL making it optional. Thus you can also write

mySubroutine(13,"apple","pie")

You can also omit the opening and closing parentheses, thus it becomes:

CALL mySubroutine 13,"apple","pie"

or

mySubroutine 13,"apple","pie"

with this features ScriptBasic for Java can be used as a simple domain specific language implementation.