Decorators

Decorators provide compile-time metadata attached to definitions.

Policy (Constraints)

Decorators are intentionally narrow:

• Decorators MUST NOT be used to model domain semantics (e.g. database schemas/ORM, SQL, HTTP, validation rules).
• Integration behavior belongs in typed values (e.g. Source configurations) and types (decoders), not hidden in decorators.
• Only the standard decorators listed here are allowed in v0.1. Unknown decorators are a compile error.
• User-defined decorators are not supported in v0.1.

14.1 Syntax

@decorator_name
@decorator_name value
@decorator_name { key: value }

Decorators appear before the binding they annotate.

14.2 Standard Decorators

Compile-Time

Decorator	Usage	Meaning
@static	@static x = file.read "..."	Embed at compile time
@inline	@inline f = ...	Always inline function
@deprecated	@deprecated msg	Emit warning on use

Tooling (MCP)

Decorator	Usage	Meaning
@mcp_tool	@mcp_tool fetchData = ...	Expose as MCP tool
@mcp_resource	@mcp_resource config = ...	Expose as MCP resource

Testing

Decorator	Usage	Meaning
@test	@test add_is_commutative = ...	Mark a definition as a test case

Pragmas (Module-level)

Decorator	Usage	Meaning
@no_prelude	@no_prelude module M	Skip implicit prelude import

14.3 Decorator Desugaring

Decorators desugar to compile-time metadata:

Surface	Desugared
@static x = file.read ...	Compile-time evaluation
@mcp_tool f = ...	Register in MCP manifest

14.4 Usage Examples

Compile-Time Embedding

@static
version : Text
version = file.read "./VERSION"

@static
schema : JsonSchema
schema = file.json "./schema.json"

MCP Tools

@mcp_tool
searchDocs : Query -> Effect Http (List Document)
searchDocs query = http.get "https://api.example.com/search?q={query}"

@mcp_resource
appConfig : Source File Config
appConfig = file.json "./config.json"