Semantic Analysis: Names, Scopes, and Rules

Why this module exists

Parsing gives structure, but not meaning. Semantic analysis answers questions like:

• Is a variable declared before it is used?
• Is a const being reassigned?
• Does a return appear outside a function?

These checks make programs understandable before running them.

1) Scopes

Each block introduces a new scope. A scope holds bindings:

• name
• kind (var/const/function/param)

Lookups search from inner to outer scope.

2) Core rules for this pack

We enforce these rules:

• No duplicate declarations in the same scope
• Names must be declared before use
• const must be initialized and cannot be reassigned
• return only inside a function
• Function calls must match a known function's arity

We do not type-check expressions. The language is dynamic.

3) Readable errors

Semantic errors should be short and clear. Examples:

• "undefined name: x"
• "redeclare in same scope: x"
• "cannot assign to const: pi"
• "return outside function"
• "arity mismatch: add expects 2"

4) Open-ended design

You could add:

• type checks
• closures and upvalues
• modules and imports

The core idea is to keep the analysis phase explicit and easy to reason about.