Function parameters

Functions can take parameters, to specialize their behavior.

Purpose of function parameters

The function declaration specifies the name of the function and the identifiers of its formal arguments (if any).

Function parameters hold values passed by the caller, to be used in the body of the function.

Function parameter specification with legacy syntax

With the legacy function definition syntax, the data type of each formal argument of the function must be specified by a DEFINE statement that immediately follows the argument list.
FUNCTION check_address(zipcode, street, city)
  DEFINE zipcode CHAR(5),
         street VARCHAR(100),
         city VARCHAR(50)
  DEFINE found BOOLEAN -- local function variable
  ...
END FUNCTION

Function parameter specification with fully-typed syntax

With the fully-typed function definition syntax, the type of the parameters is specified inside the parentheses:
FUNCTION check_address(zipcode CHAR(5), street VARCHAR(100), city VARCHAR(50))
  DEFINE found BOOLEAN -- local function variable
  ...
END FUNCTION

Function without parameters

If no argument is needed in a function call, an empty argument list must still be supplied, enclosed between the parentheses:
FUNCTION begin_work()
   ...
END FUNCTION

Passing primitive type values as parameters

Function arguments using simple data types such as INTEGER are passed by value (the values are copied on the stack).

In the following code example, the variable x defined in the MAIN block will not be modified by the function:

MAIN
  DEFINE x INTEGER
  LET x = 123
  CALL myfunc(x)
  DISPLAY x   -- displays 123
END MAIN

FUNCTION myfunc(x)
  DEFINE x INTEGER
  LET x = x + 1
END FUNCTION
Note: Parameters of type TEXT and BYTE are also passed by value, but it's only the large object handler which is copied on the stack. The actual data is pointed to by the handler and therefore it is not copied.

Type conversions

The actual argument in a call to the function need not be of the declared data type of the formal argument. The runtime system will do the appropriate data type conversions when needed. If the data type conversion is not possible, a runtime error occurs.

Genero BDL data type conversion is quite permissive by default. The following example will not raise an error, because the string value is silently converted to a NULL INTEGER:
MAIN
    CALL add("aaaaa")
END MAIN

FUNCTION add(x)
    DEFINE x INTEGER
    DISPLAY "x = ", x
END FUNCTION

Passing complex objects as parameters

Complex structures such as dynamic arrays and objects are passed by reference: The reference of the complex object is copied on the stack and can be used as is inside the function:
MAIN
    DEFINE ch base.Channel
    LET ch = base.Channel.create()
    CALL ch.openFile(arg_val(1), "r")
    CALL read_lines(ch)
END MAIN

FUNCTION read_lines(ch base.Channel)
    DEFINE s STRING
    WHILE TRUE
        LET s = ch.readLine()
        IF ch.isEOF() THEN EXIT WHILE END IF
        DISPLAY s
    END WHILE
END FUNCTION

Passing records by reference

By default, records are expanded on the stack: Each field of the record is passed by value like a primitive data type.

Records can be passed by reference, when specifying the INOUT keyword in the function definition:
FUNCTION init_cust(r CustRec INOUT)
    LET r.cust_id = 0
    LET r.cust_name = "<undefined>"
    LET r.cust_addr = "<undefined>"
    LET r.cust_crea = CURRENT
END FUNCTION
Important: Passing records by reference with INOUT is only supported when the called function is defined locally, or is known by the compiler because it was imported with IMPORT FGL.

For more details, see Passing records as parameter.