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use std::borrow::Borrow;
use std::collections::HashMap;
use std::hash::Hash;
use std::mem;
use std::rc::Rc;
use super::Term;
#[derive(Debug, Default)]
pub struct Context {
bindings: Vec<String>,
variables: HashMap<String, Term>,
functions: HashMap<String, (Rc<dyn Convert>, Vec<String>)>,
}
impl Context {
/// # Examples
/// ```
/// use chomp::ast::convert::Context;
///
/// let context = Context::new();
/// assert_eq!(context.get("x"), None);
/// assert_eq!(context.get("y"), None);
/// assert_eq!(context.get("z"), None);
/// ```
pub fn new() -> Self {
Self::default()
}
/// # Errors
/// Returns [`None`] if `name.is_empty()` or if `name` is unbound.
///
/// # Examples
/// ```
/// use chomp::ast::convert::Context;
///
/// let context = Context::new();
/// assert_eq!(context.get("x"), None);
///
/// context.push("x".to_owned(), |c| {
/// assert_eq!(c.get("x"), Some(0));
///
/// c.push("y".to_owned(), |c| {
/// assert_eq!(c.get("x"), Some(1));
/// })
/// });
///
/// assert_eq!(context.get("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
}
/// # Panics
/// If `name.is_empty()`.
///
/// # Examples
/// ```
/// use chomp::ast::convert::Context;
///
/// let context = Context::new();
/// assert_eq!(context.get("x"), None);
///
/// context.push("x".to_owned(), |c| {
/// assert_eq!(c.get("x"), Some(0));
/// });
///
/// assert_eq!(context.get("x"), None);
/// ```
pub fn push_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
}
/// # Errors
/// If `name == "".to_owned().borrow()` or `name` is unbound.
pub fn get_variable<T: ?Sized + Hash + Eq>(&self, name: &T) -> Option<&Term>
where
String: Borrow<T>,
{
if name == "".to_owned().borrow() {
return None
}
self.variables.get(name)
}
/// # Panics
/// If any variable name is empty.
pub fn add_function(&mut self, name: String, source: Rc<dyn Convert>, variables: Vec<String>) {
if variables.iter().any(|s| s.is_empty()) {
panic!()
}
self.functions.insert(name, (source, variables));
}
/// This uses dynamic scope for bindings.
/// # Errors
/// If `name` is unbound or has been called with the wrong number of arguments.
pub fn call_function<I: IntoIterator<Item = Term>, T: ?Sized + Hash + Eq>(
&mut self,
name: &T,
args: I,
) -> Option<Term>
where
String: Borrow<T>,
<I as IntoIterator>::IntoIter: ExactSizeIterator,
{
let (term, vars) = self.functions.get(name)?;
let args_iter = args.into_iter();
if vars.len() != args_iter.len() {
None
} else {
let mut old = Vec::new();
for (var, value) in vars.clone().into_iter().zip(args_iter) {
if let Some((old_name, old_value)) = self.variables.remove_entry(var.borrow()) {
let mut indices = Vec::new();
for (index, binding) in self.bindings.iter_mut().enumerate() {
if *binding == old_name {
indices.push((index, mem::take(binding)));
}
}
old.push((old_name, old_value, indices))
}
self.variables.insert(var, value);
}
let res = Some(term.clone().convert(self));
for (name, value, indices) in old {
for (index, binding) in indices {
self.bindings[index] = binding
}
self.variables.insert(name, value);
}
res
}
}
}
pub trait Convert: std::fmt::Debug {
fn convert(&self, context: &mut Context) -> Term;
}
|
