Modules

Modules are the most important feature distinguishing Modula-2 from its ancestor, Pascal. We have already encountered modules, simply because every program is a module. However, most programs are partitioned into several modules, each module containing constants, variables, procedures, and perhaps types. Objects declared in other modules can be referenced in a module M, if they are explicitly made to be known in M, i.e. if they are imported into M. In the examples of the preceding chapters, we have typically imported procedures for input and output from modules containing collections of frequently used procedures. These procedures are actually part of our program, even if we have not programmed them and they are textually disjoint.