Included files can be nested; that is, each file can contain include statements. For example, suppose that a program contains the statement:

 

include "graphics.inc"

 

The GRAPHICS.INC file might contain the statement:

 

include "boxes.inc"

 

The BOXES.INC file might contain the statement:

 

include "points.inc"

 

You can nest include statements to 20 levels. Make sure that no file includes itself or any other file that has already been included. In the example above, the POINTS.INC file must not specify include statements for the GRAPHICS.INC or BOXES.INC files. If it does, each of the two files will cause the other file to become part of it each time ESL encounters the include statement, and inclusion will never end.

 

ESL generates error messages if you specify an invalid filename or too many levels of nesting, or if the specified file cannot be accessed or opened.