Module system

A module collects related types, functions, or other declarations into a named unit. Clients access its definitions through imports or qualified names. This supports separate maintenance and namespaces that reduce naming conflicts. Modules may correspond to files, but the language determines that mapping rather than requiring every logical boundary to follow directory layout.

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An interface specifies the names and types that clients may rely on while hiding implementation details. An OCaml signature can expose an abstract type with operations without revealing its storage representation. Implementations can then change behind the interface, provided the promised behavior remains compatible with what existing clients are entitled to expect.

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Imports establish dependencies and may execute initialization code. Python distinguishes a module’s namespace from that of its importer and keeps records of imported modules. Work placed at the top level can therefore affect import behavior. Initialization, circular dependencies, and the program’s execution entry point need deliberate organization rather than accidental ordering.

References: [1]

Some systems parameterize modules with other modules. An OCaml functor accepts a component satisfying a signature and constructs an implementation around it, such as an ordered collection using a supplied comparison rule. Reuse then covers cooperating definitions as a group, with interfaces constraining both the input component and the resulting module.

References: [2]