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use std::collections::HashMap;
use std::hash::Hash;
pub struct Environment<'a, T: 'a, U: 'a> {
pub parent: Option<&'a Environment<'a, T, U>>,
pub bindings: HashMap<T, U>,
}
impl<'a, T: 'a, U: 'a> Environment<'a, T, U>
where T: Eq + Hash {
pub fn new(parent: Option<&'a Environment<'a, T, U>>) -> Environment<'a, T, U> {
Environment {
parent: parent,
bindings: HashMap::new(),
}
}
pub fn set_parent(&mut self, parent: &'a Environment<'a, T, U>) {
self.parent = Some(parent);
}
pub fn add_binding(&mut self, key: T, value: U) {
self.bindings.insert(key, value);
}
pub fn lookup(&self, key: &T) -> Option<&U> {
if let Some(v) = self.bindings.get(key) {
Some(v)
}
else if let Some(p) = self.parent {
p.lookup(key)
}
else {
None
}
}
}
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