Modules

Limbo supports compartmentalization of functionality through the dynamic loading and unloading of names and definitions through modules.

A particular module may include a .m file module definition associated with a given implementation of said module contained within .b files.

Disclaimer: At the time of writing I am not exceptionally well-versed with modules in Limbo. All assertions should be taken with a grain of salt.

Source

persons.m:1,11

The Persons module exposes three functions and an ADT.

Function definitions:

• init() -- persons.b:7,9
• mkperson() -- persons.b:11,13
• getpop() -- persons.b:15,18

Note: In a way, a module definition acts as an interface which dictates which functions, variables, and types are accessible from outside the module's implementation proper.

towns.m:1,14

The Towns module exposes two functions, a variable, and an ADT.

Note that the module file includes persons.m to allow it to utilize the Persons definition, allowing a handle to be attached to the module Persons within the module Towns as per the Towns->init() definition.

Function definitions:

• init() -- towns.b:5,7
• mktown() -- towns.b:9,11

modules.b:25,29

This section loads the auxiliary modules used within this example and calls their respective initialization functions.

Note that no module should be considered usable or safe to reference before calling their respective initialization function, if any.

modules.b:31,39

This section demonstrates calling the getpop() function within the Persons module using the currently loaded handle to the Persons module, persons. An instance of ref Person is created and its fields filled manually.

Note that across these two calls, the population within modules->persons increments, however, the population within towns->persons does not increment. This is because the two instances of the Persons module are separate and loaded separately. These two modules share no resources other than a common origin within their .dis bytecode files.

modules.b:41,45

This section features a call to mktown() from within the Towns module. The contents of the respective ref Town are filled manually.

Note: The type Person is imported at modules.b:13.

Demo

; mk
; modules
0
0
1
0
Name: Mars
Size: 2
Members:
→ Spike
→ Ed
; 

Exercises

• Can you access persons->population from modules?
• Could you make a global variable by placing said variable in its respective module definition?
• What happens if you remove the import statements for Person and Town in various .b files?
• What happens if you include persons.m in modules.b?
• What happens if you include persons.m in modules.b and remove the include for persons.m in towns.m?
• Can you load the Util module contained within util.b?