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use std::borrow::Borrow;
use std::collections::HashMap;
use std::hash::Hash;
use super::Term;
#[derive(Debug, Default)]
/// The variable context for converting a concrete syntax tree to an abstract
/// one.
///
/// There are two name scopes in a context. Bindings are used by fixed points.
/// Variables are formal parameters of macros.
pub struct Context {
bindings: Vec<String>,
variables: HashMap<String, usize>,
}
impl Context {
/// Creates a new variable context. No names are bound.
pub fn new() -> Self {
Self::default()
}
/// Returns [`Some`] index of a binding `name`.
///
/// # Errors
/// Returns [`None`] if `name.is_empty()` or if `name` is unbound.
///
/// # Examples
/// ```
/// use chomp::ast::convert::Context;
///
/// let mut context = Context::new();
/// assert_eq!(context.get_binding("x"), None);
///
/// context.with_binding("x".to_owned(), |c| {
/// assert_eq!(c.get_binding("x"), Some(0));
///
/// c.with_binding("y".to_owned(), |c| {
/// assert_eq!(c.get_binding("x"), Some(1));
/// })
/// });
///
/// assert_eq!(context.get_binding("x"), None);
/// ```
pub fn get_binding<T: ?Sized + PartialEq<str>>(&self, name: &T) -> Option<usize> {
let mut iter = self.bindings.iter();
let mut pos = 0;
if name == "" {
return None;
}
while let Some(var) = iter.next_back() {
if T::eq(&name, &var) {
return Some(pos);
} else {
pos += 1;
}
}
None
}
/// Adds a binding `name` for the duration of the function `f`.
///
/// # Panics
/// If `name.is_empty()`.
///
/// # Examples
/// ```
/// use chomp::ast::convert::Context;
///
/// let mut context = Context::new();
/// assert_eq!(context.get_binding("x"), None);
///
/// context.with_binding("x".to_owned(), |c| {
/// assert_eq!(c.get_binding("x"), Some(0));
/// });
///
/// assert_eq!(context.get_binding("x"), None);
/// ```
pub fn with_binding<F: FnOnce(&mut Self) -> T, T>(&mut self, name: String, f: F) -> T {
if name.is_empty() {
panic!()
}
self.bindings.push(name);
let res = f(self);
self.bindings.pop();
res
}
/// Returns [`Some`] index of a variable `name`.
///
/// # Errors
/// If `name == "".to_owned().borrow()` or `name` is unbound.
///
/// # Examples
/// ```
/// use chomp::ast::convert::Context;
///
/// let mut ctx = Context::new();
/// assert_eq!(ctx.get_variable("x"), None);
///
/// ctx.set_variables(vec!["x".to_owned(), "y".to_owned()]);
/// assert_eq!(ctx.get_variable("x"), Some(0));
/// assert_eq!(ctx.get_variable("y"), Some(1));
///
/// ctx.set_variables(vec![]);
/// assert_eq!(ctx.get_variable("x"), None);
/// ```
pub fn get_variable<T: ?Sized + Hash + Eq>(&self, name: &T) -> Option<usize>
where
String: Borrow<T>,
{
if name == "".to_owned().borrow() {
return None;
}
self.variables.get(name).copied()
}
/// Reassigns all variable indices based off of their position in `args`.
///
/// # Examples
/// ```
/// use chomp::ast::convert::Context;
///
/// let mut ctx = Context::new();
/// assert_eq!(ctx.get_variable("x"), None);
///
/// ctx.set_variables(vec!["x".to_owned(), "y".to_owned()]);
/// assert_eq!(ctx.get_variable("x"), Some(0));
/// assert_eq!(ctx.get_variable("y"), Some(1));
///
/// ctx.set_variables(vec![]);
/// assert_eq!(ctx.get_variable("x"), None);
/// ```
pub fn set_variables<I: IntoIterator<Item = String>>(&mut self, args: I) {
self.variables = args
.into_iter()
.enumerate()
.map(|(index, name)| (name, index))
.collect();
}
}
/// Used to convert a concrete term into an abstract term.
pub trait Convert {
/// Performs the conversion.
fn convert(&self, context: &mut Context) -> Term;
}
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