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use std::collections::HashMap;
use std::fmt::{self, Debug, Formatter};
use std::iter;
use super::Value;
/// A hierarchy 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 }
}
/// Look up the value of a variable in the scopes.
pub fn get(&self, var: &str) -> Option<&Value> {
iter::once(&self.top)
.chain(&self.scopes)
.chain(iter::once(self.base))
.find_map(|scope| scope.get(var))
}
/// Define a variable in the active scope.
pub fn define(&mut self, var: impl Into<String>, value: impl Into<Value>) {
self.top.set(var, value);
}
}
/// 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()
}
/// Look up the value of a variable.
pub fn get(&self, var: &str) -> Option<&Value> {
self.values.get(var)
}
/// Store the value for a variable.
pub fn set(&mut self, var: impl Into<String>, value: impl Into<Value>) {
self.values.insert(var.into(), value.into());
}
}
impl Debug for Scope {
fn fmt(&self, f: &mut Formatter) -> fmt::Result {
self.values.fmt(f)
}
}
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