3.1.5 Include Files

MDL files can be split into several convenient parts and combined as needed by using #include statements. An #include statement causes the MDL interpreter to insert the contents of the requested file.

#include "filename"

To support structured libraries of MDL #include files the environment variable VMODELPATH can be used. It determines a list of directories where the MDL interpreter searches for files to be included. The following strategy is followed:

• If filename gives the absolute path of the include file, the file is included if it exists at this path. Otherwise an error message is raised.
• If filename gives only the filename or a relative path specification the MDL interpreter looks for the include file in the working directory at first. If it is not found there it is searched in each of the paths given by the environment variable VMODELPATH in the therein defined order. This search is immediately aborted when a corresponding file is found without looking for synonymous files at the remaining paths. An optional relative path string within the #include statement is taken into account for all these tests. Again an error message is given if the files was not found in any of these locations.

The syntax for path strings and path delimiters in the environment string follows the common rules for such constructs on the actual operating system in use. Example 3.4 gives an example for the usage of environment variables supporting the lookup of #include files on Unix compatible Systems. The analogous Windows-NT compatible syntax is demonstrated in Example 3.5.

set $VMODELPATH   = "$VPROJECT/promisnt/mdl:$VROOT/mdl";
#include "basics.mdl"
#include "$VPROJECT/promisnt/exa/test.mdl"

Example 3.4: Include statements for Unix compatible systems

set $VMODELPATH   = "$VPROJECT promisnt mdl:$VROOT mdl";
#include "basics.mdl"
#include "$VPROJECT promisnt exa test.mdl"

Example 3.5: Include statements for Windows-NT compatible systems

Directories stated in VMODELPATH which do not exist are silently ignored.