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use std::cell::RefCell;
use std::collections::HashMap;
use std::fmt::{self, Debug, Formatter};
use std::iter;
use std::rc::Rc;
use super::Value;
/// A slot where a variable is stored.
pub type Slot = Rc<RefCell<Value>>;
/// A stack of scopes.
#[derive(Default, Debug, Clone, PartialEq)]
pub struct Scopes<'a> {
/// The active scope.
pub top: Scope,
/// The stack of lower scopes.
pub scopes: Vec<Scope>,
/// The base scope.
pub base: Option<&'a Scope>,
}
impl<'a> Scopes<'a> {
/// Create a new, empty hierarchy of scopes.
pub fn new() -> Self {
Self {
top: Scope::new(),
scopes: vec![],
base: None,
}
}
/// Create a new hierarchy of scopes with a base scope.
pub fn with_base(base: &'a Scope) -> Self {
Self {
top: Scope::new(),
scopes: vec![],
base: Some(base),
}
}
/// Enter a new scope.
pub fn enter(&mut self) {
self.scopes.push(std::mem::take(&mut self.top));
}
/// Exit the topmost scope.
///
/// # Panics
/// Panics if no scope was entered.
pub fn exit(&mut self) {
self.top = self.scopes.pop().expect("no pushed scope");
}
/// Define a constant variable with a value in the active scope.
pub fn def_const(&mut self, var: impl Into<String>, value: impl Into<Value>) {
self.top.def_const(var, value);
}
/// Define a mutable variable with a value in the active scope.
pub fn def_mut(&mut self, var: impl Into<String>, value: impl Into<Value>) {
self.top.def_mut(var, value);
}
/// Define a variable with a slot in the active scope.
pub fn def_slot(&mut self, var: impl Into<String>, slot: Slot) {
self.top.def_slot(var, slot);
}
/// Look up the slot of a variable.
pub fn get(&self, var: &str) -> Option<&Slot> {
iter::once(&self.top)
.chain(self.scopes.iter().rev())
.chain(self.base.into_iter())
.find_map(|scope| scope.get(var))
}
}
/// A map from variable names to variable slots.
#[derive(Default, Clone, PartialEq)]
pub struct Scope {
/// The mapping from names to slots.
values: HashMap<String, Slot>,
}
impl Scope {
/// Create a new empty scope.
pub fn new() -> Self {
Self::default()
}
/// Define a constant variable with a value.
pub fn def_const(&mut self, var: impl Into<String>, value: impl Into<Value>) {
let cell = RefCell::new(value.into());
// Make it impossible to write to this value again.
// FIXME: Use Ref::leak once stable.
std::mem::forget(cell.borrow());
self.values.insert(var.into(), Rc::new(cell));
}
/// Define a mutable variable with a value.
pub fn def_mut(&mut self, var: impl Into<String>, value: impl Into<Value>) {
self.values.insert(var.into(), Rc::new(RefCell::new(value.into())));
}
/// Define a variable with a slot.
pub fn def_slot(&mut self, var: impl Into<String>, slot: Slot) {
self.values.insert(var.into(), slot);
}
/// Look up the value of a variable.
pub fn get(&self, var: &str) -> Option<&Slot> {
self.values.get(var)
}
}
impl Debug for Scope {
fn fmt(&self, f: &mut Formatter) -> fmt::Result {
self.values.fmt(f)
}
}
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