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use std::collections::HashMap;
use std::fmt::{self, Debug, Formatter};
use std::iter;
use super::Value;
/// A stack of scopes.
#[derive(Debug, Clone, PartialEq)]
pub struct Scopes<'a> {
/// The active scope.
top: Scope,
/// The stack of lower scopes.
scopes: Vec<Scope>,
/// The base scope.
base: &'a Scope,
}
impl<'a> Scopes<'a> {
/// Create a new hierarchy of scopes.
pub fn new(base: &'a Scope) -> Self {
Self { top: Scope::new(), scopes: vec![], base }
}
/// Push a new scope.
pub fn push(&mut self) {
self.scopes.push(std::mem::take(&mut self.top));
}
/// Pop the topmost scope.
///
/// # Panics
/// Panics if no scope was pushed.
pub fn pop(&mut self) {
self.top = self.scopes.pop().expect("no pushed scope");
}
/// Define a variable in the active scope.
pub fn define(&mut self, var: impl Into<String>, value: impl Into<Value>) {
self.top.define(var, value);
}
/// Look up the value of a variable.
pub fn get(&self, var: &str) -> Option<&Value> {
iter::once(&self.top)
.chain(self.scopes.iter().rev())
.chain(iter::once(self.base))
.find_map(|scope| scope.get(var))
}
/// Get a mutable reference to a variable.
pub fn get_mut(&mut self, var: &str) -> Option<&mut Value> {
iter::once(&mut self.top)
.chain(self.scopes.iter_mut().rev())
.find_map(|scope| scope.get_mut(var))
}
/// Return whether the variable is constant (not writable).
///
/// Defaults to `false` if the variable does not exist.
pub fn is_const(&self, var: &str) -> bool {
self.base.get(var).is_some()
}
}
/// A map from variable names to values.
#[derive(Default, Clone, PartialEq)]
pub struct Scope {
values: HashMap<String, Value>,
}
impl Scope {
/// Create a new empty scope.
pub fn new() -> Self {
Self::default()
}
/// Define a new variable.
pub fn define(&mut self, var: impl Into<String>, value: impl Into<Value>) {
self.values.insert(var.into(), value.into());
}
/// Look up the value of a variable.
pub fn get(&self, var: &str) -> Option<&Value> {
self.values.get(var)
}
/// Get a mutable reference to a variable.
pub fn get_mut(&mut self, var: &str) -> Option<&mut Value> {
self.values.get_mut(var)
}
}
impl Debug for Scope {
fn fmt(&self, f: &mut Formatter) -> fmt::Result {
self.values.fmt(f)
}
}
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