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use std::rc::Rc;
use super::{Scope, Scopes, Value};
use crate::syntax::visit::{immutable::visit_expr, Visit};
use crate::syntax::{Expr, Ident};
/// A visitor that captures variable slots.
#[derive(Debug)]
pub struct CapturesVisitor<'a> {
external: &'a Scopes<'a>,
internal: Scopes<'a>,
captures: Scope,
}
impl<'a> CapturesVisitor<'a> {
/// Create a new visitor for the given external scopes.
pub fn new(external: &'a Scopes) -> Self {
Self {
external,
internal: Scopes::new(None),
captures: Scope::new(),
}
}
/// Return the scope of captured variables.
pub fn finish(self) -> Scope {
self.captures
}
}
impl<'ast> Visit<'ast> for CapturesVisitor<'_> {
fn visit_expr(&mut self, node: &'ast Expr) {
if let Expr::Ident(ident) = node {
// Find out whether the name is not locally defined and if so if it
// can be captured.
if self.internal.get(ident).is_none() {
if let Some(slot) = self.external.get(ident) {
self.captures.def_slot(ident.as_str(), Rc::clone(slot));
}
}
} else {
visit_expr(self, node);
}
}
fn visit_binding(&mut self, id: &'ast Ident) {
self.internal.def_mut(id.as_str(), Value::None);
}
fn visit_enter(&mut self) {
self.internal.enter();
}
fn visit_exit(&mut self) {
self.internal.exit();
}
}
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