Macro Command Language Gets Even More Powerful

Since their first introduction, way back in Release 2.0, the possibilities offered by EMME/2 macros have been steadily increased. The initially ``dumb'' file play back mechanism has in the mean time become a complete macro programming environment.

Release 6.0 continues in this tradition by enhancing the macro command language even further, offering new possibilities for macro writers that go far beyond what was possible up to now.

As this is not the place for explaining all the technical details that are important for the experts in macro writing, here is just a brief list of the most important new possibilities, without getting too technical:

• Up to 10 new text registers, t0 - t9, can be used to store textual information in addition to the already existing numerical registers. These text registers can be manipulated, compared and tested for specified values.
• The text register t0 corresponds to the macro invocation parameters opens the possibility to implement default values for macro parameters, or assign new values to these parameters. The same mechanism can also be used in order to split a text input into individual words.
• The names and descriptions of scalars can now be accessed in macros, using the new substitutions text of the scalar.
• An optional prompt string can now follow the ~* command for interactive text entry. This text will be displayed to prompt the user, replacing the default prompt ``>>''.
• The access to data bank parameters has been greatly enhanced. The new parameter register p can be used to access global, scenario and system parameters. System parameters include information such as licence number, licence size, host operating system (important if macro uses OS command escapes), CPU time and current time/date information.
• The possibilities of error recovery have been improved. Macros can now sense the error number of the last error that occurred, as well as access the accumulated total number of errors of type fatal or warning. This allows e.g. a macro to detect and react to warnings, which was not possible in earlier versions. When a macro fails due to a fatal error (i.e. if the error is not caught and acted upon by the macro itself), a message is displayed indicating the file name and the line of the macro in which the error occurred.
• Last but not least, one of the most important new features is no doubt the possibility for the macro to control the dialog output. So far, we associate running a macro with having lots of dialog questions and answers scrolling at great speed over the screen. In Release 6.0, it is possible to control exactly which part of the dialog input and output is to be sent to the terminal and which part is to be suppressed - or even saved into a text register. This way, macros can have their own identity, by suppressing the dialog of the invoked modules and setting up their own front end instead. Thus, the macro user is no longer exposed to details of the macro implementation which are not important to him; instead he can concentrate on the essentials.