handl

Platform architecture ​

The handl platform is a workspace of Rust crates organised around one goal: every concept in the language is a Plugin, and every tool is a Host that composes plugins.

Crate layers ​

text
handl-host-cli, handl-host-lsp     # executable hosts
handl-ext-fmt, handl-ext-lint,    # concrete operations
  handl-ext-lexer, handl-ext-parser,
  hnl-engine-typecheck, handl-ext-cli,
  handl-ext-lsp, handl-ext-doc,
  handl-ext-eval
handl-plugin-*                    # rule and library plugins
handl-kit-*                       # curated kit manifests
handl-target-*                    # runtime targets
handl-platform                    # Plugin, Host, and composition primitives
LayerResponsibility
handl-platformHost, Plugin, RuleAcceptor, Operation, Behavior, ContributionContext, Options, AstNode, and resolution.
handl-ext-*Concrete operations such as Format, Lint, Parser, Lexer, Typecheck, Eval, Cli, Lsp, and Doc.
handl-plugin-*Rule plugins that contribute Behaviors and OptionSchemas, and library plugins that register more plugins.
handl-kit-*Curated manifests of plugins and default option values. A kit is not executable.
handl-target-*Target plugins that register runtime backends.
handl-host-*Executable hosts that load kits and execute Cli or Lsp capabilities.

Why this split ​

The platform crate intentionally stays small. It defines the composition primitives and nothing else. Concrete operations, library rules, and targets live in separate crates because they can be added, swapped, or excluded without changing the core. This lets a host be as small as a formatter or as large as a language server.

The host as composer ​

A Host starts empty and ends as a fully composed tool. It does this by:

  1. Loading HostConfig from a HostApplier.
  2. Merging kit manifests into PluginRegistry.
  3. Resolving requires and optional dependencies.
  4. Running Plugin::contribute in topological order.
  5. Repeating steps 3–4 until no new plugins appear.
  6. Resolving Options from merged schemas and overrides.

After this, Host::execute dispatches a CapabilityRequest to the plugin that provides the requested capability.

Adding a new operation ​

To add a new operation such as Hover:

  1. Create handl-ext-hover.
  2. Define a Hover marker type implementing Operation.
  3. Define HoverBehavior implementing Behavior<Hover>.
  4. Provide BasicHover as a RuleAcceptor<Rule = HoverBehavior>.
  5. Register BasicHover in the host.

No handl-platform change is required.