4. Programs, names and scope

A source file is a module. Its path is given by module a.b.c or, if absent, by its file path relative to the package root with / read as . and the .rce extension removed. use p.q makes module p.q visible under the name q; use p.q as r under r. Items are private to their module unless marked pub. Import cycles are refused (W-MOD-2). The modules std.text, std.collections and std.math are built in and always resolvable (S4); a program is the set of modules given together, and use must name one of them or a built-in module (W-NAME-1).

A Form module is a module (with what it imports) that declares at least one state, event or actor. The Form of the program is built from all Form modules reachable from the root (6.1). A module with only fn, types, const and impl is a library module: it has no Form of its own and denotes a set of pure functions.

A program whose root declares fn main() and no state is a command: it denotes the Form with one region Main of unit type, one event Start(args: List[text]), and δ given by running main (6.8).

Scopes nest: universe (built-in types and functions, 6.3–6.4) ⊃ package ⊃ module ⊃ item (generic parameters, parameters, state fields inside steps) ⊃ block. Declarations at module level are visible throughout the module regardless of order (so const N may follow its use). Inside a block a name is visible from its declaration to the end of the block. Shadowing a name from an enclosing block is allowed with let; shadowing a parameter, a state field or a module-level name in the same item is refused (W-NAME-2).

Namespaces: one namespace for values (variables, functions, consts, variants, events, errors) and one for types (types, kinds, traits, states, actors). Event, error and variant constructors live in both: as types (for patterns and payload typing) and as constructor functions.