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|Access resources using open_resource
Before the system had the ability to open resources as files, resources were opened using the predicates open_resource/2 or open_resource/3. These predicates provide somewhat better dynamic control over resources depending on whether the code is running from files or from a saved state. The main disadvantage is that having a separate open call requires rewriting code to make it work with resources rather than files.
The predicate open_resource/3 first checks resource/2. When successful it will open the returned resource source file. Otherwise it will look in the program's resource database. When creating a saved state, the system normally saves the resource contents into the resource archive, but does not save the resource clauses.
This way, the development environment uses the files (and modifications) to the resource/3 declarations and/or files containing resource info, thus immediately affecting the running environment, while the runtime system quickly accesses the system resources.