Package

What this is

A Package is a named carrier equipped with an explicit boundary signature.

The mathematical invariant comes from module theory in programming language semantics (ML structures, Standard ML of New Jersey; Haskell modules). A module in this sense is a triple (N, C, Σ) where:

• N is the module name — a canonical identifier for the whole
• C is the carrier — the set of definitions, values, or objects that exist inside the module
• Σ ⊆ C is the signature — the subset of C that is exported (visible from outside the module boundary)

The boundary is defined by the signature: what is in Σ is public; what is in C \ Σ is private. Two modules with the same N, C, and Σ are equal regardless of their internal organization. The package identity is the pair (N, Σ) — the name and what it presents — not the internal implementation.

In type theory: a package is a record type at the collection level — the signature Σ is a record type whose fields are the exported names. Providing a package = providing a term of that record type drawn from the carrier C.

This is what distinguishes a package from a bare set or a collection: a set has no exported interface; a package explicitly declares one. The interface is the contract that consumers rely on; the carrier is what implements it.

Cohesion

The carrier C is not an arbitrary collection. Items in C are related by cohesion: they belong together because they serve the same purpose, share the same subject, or operate on the same carrier set. Cohesion is the principle that makes the package a meaningful unit rather than an arbitrary bundle.

In module theory: cohesion is enforced by the subject matter of the module — all definitions in a List module are about lists. In this system: cohesion is enforced by the concept the package organizes (see ConceptPackage).

Open questions

• Whether a package requires an explicit manifest (a declared Σ) or whether colocation alone (same directory) is sufficient to constitute a boundary.
• Whether the exported signature Σ is an additional required field or derivable from the structure of the package’s contents.