Scope of a function

A functions can be isolated to control its visibility to other modules.

A FUNCTION block cannot appear within the MAIN block, in a REPORT block, or within another FUNCTION block. A function must be declared at the root level in the source code:

MAIN
  ...
END MAIN

FUNCTION myfunc( ... )
  ...
END FUNCTION

REPORT myrep( ... )
  ...
END REPORT

By default, functions are PUBLIC; They can be called by any other module of the program.

If a function is only used by the current module, you can hide that function to other modules, to make sure that it will not be called by mistake.

To keep a function local to the module, add the PRIVATE keyword before the function header.

Private functions are only hidden to external modules, all function of the current module can still call local private functions.

PRIVATE FUNCTION check_number(n)
  ...
END FUNCTION

For better code readability, you can use the PUBLIC keyword for functions that are global and visible to all modules:

PUBLIC FUNCTION initialize()
  ...
END FUNCTION

When not using the module prefix, function symbols are global to all modules and must be unique. However, with the IMPORT FGL method, you can use the module prefix when invoking a function and simplify function naming conventions, since different modules can the define functions with the same name:

-- Module svgutils.4gl:
PUBLIC FUNCTION initialize()
  ...
END FUNCTION

-- Module sqlutils.4gl:
PUBLIC FUNCTION initialize()
  ...
END FUNCTION

-- Main program:
IMPORT FGL svgutils
IMPORT FGL sqlutils
MAIN
    CALL svgutils.initialize()
    CALL sqlutils.initialize()
    ...
END MAIN