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Converting Modules into Units

Most modules convert to units relatively easily:

• Declare the following compilation flag at the head of the main file: {$DEFINE MonoProg}. Each of the following structures to be inserted into the module should have as its alternative its original form from the main program, controlled by checking this compilation flag.

• prepend to the module's main file a UNIT interface section. The unit name can be the same as the program name. It need export only the routine that will run the module. The routine should take no parameters. Note that all the unit's global declarations should be in the IMPLEMENTATION section. The MonoProg flag will control whether this interface or the old program heading is compiled.

  One scheme is to name each such routine Activity n, n being the number of the module.

• turn the body of the former main program into the routine being exported by inserting the procedure heading for the exported routine just ahead of its BEGIN statement. Attempting to nest the whole module's code inside this routine is unnecessary, and can result in scoping problems for the module's USES statement, which must be global to the IMPLEMENTATION section.

  Whether this new header is compiled depends on the presence of the MonoProg flag.

• the END. that used to end the main program now ends the unit, so insert an END; just ahead of the END. . Again, control its presence with the MonoProg flag.

• avoid adding a BEGIN to the END., which would create an initialization body (even if empty) for the unit. The reasons for avoiding unneeded initialization bodies in units that implement modules are discussed under overlaying.

• Place at the head of the file the compilation switches {$F+,O+}. These make sure the unit will be compiled to allow calls from any distance across the segments of 808*6 memory, and can be controlled by the overlay manager. Note that these switches need not be conditionally compiled, since they make no difference to compilation as an independent program.

  Only compilation modules compiled with these switches can be overlaid.

Note that if the MonoProg flag is not defined (by changing its declaration to {$UNDEF MonoProg}) this arrangement will cause the module to continue to compile into its own program, rather than a unit.

The Activity n routine that each module's unit now exports will be called by the attract mode.

• Units Belonging to Modules