Trait DecoratorPlugin 

pub trait DecoratorPlugin: Send + Sync {
    // Provided methods
    fn pre_eval(
        &self,
        _eval: &dyn Evaluator,
        _node: &Node,
        _scope: &Arc<Scope>,
        _args: &[CallArg],
        _range: TokenRange,
    ) -> Result<PreEvalOutcome, RuntimeError> { ... }
    fn wrap(
        &self,
        _eval: &dyn Evaluator,
        value: Value,
        _scope: &Arc<Scope>,
        _args: &[EvaluatedArg],
        _range: TokenRange,
    ) -> Result<Value, RuntimeError> { ... }
    fn wrap_with_ast(
        &self,
        _eval: &dyn Evaluator,
        _node: &Node,
        _value: &Value,
        _scope: &Arc<Scope>,
        _ast_args: &[CallArg],
        _range: TokenRange,
    ) -> Result<Option<Value>, RuntimeError> { ... }
    fn schema_field_meta(
        &self,
        _eval: &dyn Evaluator,
        _field: &mut SchemaField,
        _scope: &Arc<Scope>,
        _args: &[EvaluatedArg],
        _range: TokenRange,
    ) -> Result<(), RuntimeError> { ... }
}

Hosts extend Relon’s @name(...) syntax by implementing this trait and registering an instance under the decorator’s full dotted path name (e.g. "import", "ensure.int", "my_org.audit").

Three independent hooks are exposed:

• pre_eval runs before the decorated node is evaluated. Use it to inject locals into scope (#import) or take over the value entirely (#schema).
• wrap runs after the node is evaluated. Use it to validate or transform the value (@ensure.int, @currency("USD")).
• schema_field_meta runs while extracting fields from a #schema-annotated dict. Use it to attach per-field metadata such as defaults or custom error messages (#expect, #default).

All hooks default to no-op / identity, so plugins only override what they actually need.

Provided Methods

fn pre_eval( &self, _eval: &dyn Evaluator, _node: &Node, _scope: &Arc<Scope>, _args: &[CallArg], _range: TokenRange, ) -> Result<PreEvalOutcome, RuntimeError>

fn wrap( &self, _eval: &dyn Evaluator, value: Value, _scope: &Arc<Scope>, _args: &[EvaluatedArg], _range: TokenRange, ) -> Result<Value, RuntimeError>

fn wrap_with_ast( &self, _eval: &dyn Evaluator, _node: &Node, _value: &Value, _scope: &Arc<Scope>, _ast_args: &[CallArg], _range: TokenRange, ) -> Result<Option<Value>, RuntimeError>

AST-level wrap hook. Called before Self::wrap: receives the decorator’s raw CallArg AST nodes (un-evaluated) along with the host Node so plugins that need to inspect type expressions, paths, or sibling decorators / type hints can do so without losing them to evaluation.

Returns Ok(None) to fall through to the standard wrap path. Returning Ok(Some(val)) short-circuits: wrap is not called and val becomes the decorator’s output. @brand(Type) uses this to extract the type name from the un-evaluated AST so a bareword like Weather doesn’t get resolved to a Value::Schema first.

fn schema_field_meta( &self, _eval: &dyn Evaluator, _field: &mut SchemaField, _scope: &Arc<Scope>, _args: &[EvaluatedArg], _range: TokenRange, ) -> Result<(), RuntimeError>

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors