Struct EvalSite 

pub struct EvalSite<'a> { /* private fields */ }

The site an evaluator is called from: the rule the reduction belongs to and the live parse context, and neither when evaluation is called on a finished tree.

The rule is a snapshot rather than the live rule, because the canonical port hands the evaluator the PARENT of the rule that is closing, which this engine exposes as a snapshot. Its state, its u flags and its node cell are all reachable through it.

Implementations

impl<'a> EvalSite<'a>

pub fn detached() -> Self

A site with no live parse behind it.

pub fn new(rule: Option<Rc<RuleSnapshot>>, context: &'a mut Context) -> Self

A site inside a parse.

pub fn rule(&self) -> Option<&RuleSnapshot>

The rule the reduction belongs to, when there is one.

pub fn token(&self) -> Option<&Token>

The token this OCCURRENCE of the operator was matched from.

The Op an evaluator receives is the shared description, one per entry in the operator table, so it cannot say which occurrence is being reduced. The canonical makeOp attaches the token to its copy of the description for exactly that reason; this port keeps the token beside the node instead, and hands it over here. The position is the engine’s Site triple: token.site.pos, .ri (row) and .ci (column).

It is None when the node was built without one, which is what prattify called directly produces.

pub fn context(&mut self) -> Option<&mut Context>

The live parse context, when there is one.

pub fn flag(&self, name: &str) -> bool

Whether the rule carries a u flag set to true. The paren_preval flag is what tells an evaluator that a paren operator’s first term is the preceding value.