2.4 compatibility in Nexa 3.0

This page describes the retained 2.4 language/runtime path. Sources without a version declaration use this path. Start new Open Programs with Nexa 3.0; compare contracts in the migration guide.

Algebraic data types

struct describes named fields, enum describes variants, trait describes behavior interfaces, and impl implements an interface for a type. The Python path maintains runtime registries for these definitions.

Complete declaration module

struct Point { x: int, y: int }
enum Direction { North, South }

This module compiles independently. src/runtime/adt.py and tests/test_adt.py cover fields and variants. Prefer Protocols for structured Agent output schemas; validate custom data types and model output contracts separately.

Usage and migration

The runtime supports struct instances, field reads/updates, variant construction, and trait method lookup. Keep fields explicit and design interfaces around domain operations.

The historical examples/v1.2/test_adt.nx collection fails parsing at its construction syntax on line 60 and is listed as a historical draft. Validate and execute complete examples before adopting them.

Declaration syntax and execution boundaries

Declaration	Form
struct	struct Point { x: int, y: int }
enum	enum Choice { Some(value), Empty }
trait	trait Printable { fn format() : String }
impl	impl Printable for Point { fn format() { "Point" } }

The parser and type registry support these declarations. In the current complete-program path, Point(x: 2, y: 3) raises name 'Point' is not defined; Choice::Some(42) reports a variant field-count mismatch. Both integration paths are recorded development-baseline limitations.

Use Protocols for currently executable structured model output. Trusted Python tools can manage complex local data and expose explicit JSON Schemas to Agents. ADT construction will join executable tutorials when constructor/lowering end-to-end checks pass.

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Source and validation · types