6.3 Timestamp files

Since the interface of a module changes less often than its implementation, the .int, .int0, .int2, .int3, .opt, and .trans_opt files will often remain unchanged when they are rebuilt. To avoid unnecessary recompilations of the clients of the module, the timestamps on these files are updated only if their contents change. Files with the suffixes .date, .date0, .date3, .optdate, and .trans_opt_date serve as timestamp files: they each record the last time when the file or files it represents has last been checked for being up to date. (.date files serve as the last-time-this-was-checked timestamp for both .int and .int2 files.)

The Mercury implementation uses these timestamp files when deciding whether the files they represent need to be rebuilt.