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use std::borrow::Borrow;
use std::collections::HashMap;
use std::hash::Hash;
use std::mem;
/// A lexical environment
#[derive(Debug, PartialEq, Eq)]
pub struct Env<K: Eq + Hash, V>(Vec<HashMap<K, V>>);
impl<K, V> Default for Env<K, V>
where
K: Eq + Hash,
{
fn default() -> Self {
Self::new()
}
}
impl<K, V> Env<K, V>
where
K: Eq + Hash,
{
pub fn new() -> Self {
Self(vec![Default::default()])
}
pub fn push(&mut self) {
self.0.push(Default::default());
}
pub fn pop(&mut self) {
self.0.pop();
}
pub fn save(&mut self) -> Self {
mem::take(self)
}
pub fn restore(&mut self, saved: Self) {
*self = saved;
}
pub fn set(&mut self, k: K, v: V) {
self.0.last_mut().unwrap().insert(k, v);
}
pub fn resolve<'a, Q>(&'a self, k: &Q) -> Option<&'a V>
where
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
for ctx in self.0.iter().rev() {
if let Some(res) = ctx.get(k) {
return Some(res);
}
}
None
}
}
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