use std::rc::Rc;
use super::CodeList;
use super::code_list::{ListTooLarge, PassedLimit};
use crate::core::{BindingId, Builtin, Keyword, Lambda};
use crate::reader::{Form, FormKind, NumberValue, Symbol};
#[derive(Clone, Debug, serde::Serialize, serde::Deserialize)]
pub enum Value {
Form(Form),
List(CodeList),
Bool(bool),
Unit,
Closure(Rc<Closure>),
Builtin(Builtin),
}
impl Value {
pub fn describe(&self) -> &'static str {
match self {
Value::Form(form) => Self::describe_form(form),
Value::List(_) => "a list",
Value::Bool(_) => "a boolean",
Value::Unit => "unit",
Value::Closure(_) | Value::Builtin(_) => "a function",
}
}
fn describe_form(form: &Form) -> &'static str {
match form.kind() {
FormKind::Symbol(symbol) if Keyword::field_name(symbol.name()).is_some() => "a keyword",
FormKind::Symbol(_) => "a symbol",
FormKind::String(_) => "a string",
FormKind::Number(number) => match number.value() {
NumberValue::Integer(_) => "an integer",
NumberValue::Float(_) => "a float",
},
FormKind::List(_) => "a list",
}
}
pub fn as_form(&self) -> Option<&Form> {
match self {
Value::Form(form) => Some(form),
_ => None,
}
}
pub fn to_form(&self) -> Result<Option<Form>, ListTooLarge> {
match self {
Value::Form(form) => Ok(Some(form.clone())),
Value::List(list) => list.to_form().map(Some),
_ => Ok(None),
}
}
pub fn to_form_within(
&self,
allowance: &mut usize,
enclosing_lists: usize,
) -> Result<Form, PassedLimit> {
match self {
Value::List(list) => list.to_form_within(allowance, enclosing_lists),
_ => {
*allowance = allowance.checked_sub(1).ok_or(PassedLimit::FormCount)?;
self.as_form().cloned().ok_or(PassedLimit::FormCount)
}
}
}
pub fn is_code(&self) -> bool {
matches!(self, Value::Form(_) | Value::List(_))
}
pub fn is_list(&self) -> bool {
self.as_code_list().is_some()
}
pub fn as_code_list(&self) -> Option<CodeList> {
match self {
Value::Form(form) => CodeList::of_form(form),
Value::List(list) => Some(list.clone()),
_ => None,
}
}
pub fn keyword_name(&self) -> Option<&str> {
self.as_form()
.and_then(Form::as_symbol)
.and_then(|symbol| Keyword::field_name(symbol.name()))
}
pub fn keyword_field(&self) -> Option<Form> {
let form = self.as_form()?;
let keyword = form.as_symbol()?;
let field_name = Keyword::field_name(keyword.name())?;
let field = Symbol::with_scopes(field_name, keyword.scopes().clone());
Some(Form::new(FormKind::Symbol(field), form.span()))
}
pub fn keyword_trim_end(&self) -> Option<Form> {
let form = self.as_form()?;
let keyword = form.as_symbol()?;
let trimmed = Keyword::trim_end(keyword.name())?;
let trimmed = Symbol::with_scopes(trimmed, keyword.scopes().clone());
Some(Form::new(FormKind::Symbol(trimmed), form.span()))
}
pub fn field_keyword(&self) -> Option<Form> {
let form = self.as_form()?;
let field = form.as_symbol()?;
let keyword_name = Keyword::of_field(field.name())?;
let keyword = Symbol::with_scopes(keyword_name, field.scopes().clone());
Some(Form::new(FormKind::Symbol(keyword), form.span()))
}
}
#[derive(Debug, serde::Serialize, serde::Deserialize)]
pub struct Closure {
pub lambda: Rc<Lambda>,
pub env: Env,
}
#[derive(Clone, Debug, Default, serde::Serialize, serde::Deserialize)]
pub struct Env(Option<Rc<Frame>>);
#[derive(Debug, serde::Serialize, serde::Deserialize)]
struct Frame {
binding: BindingId,
value: Value,
parent: Env,
}
impl Drop for Frame {
fn drop(&mut self) {
if self.owns_a_closure() || self.parent.is_a_sole_chain() {
ChainRelease::default().release_links_of(self);
}
}
}
impl Frame {
fn owns_a_closure(&self) -> bool {
matches!(&self.value, Value::Closure(closure) if Rc::strong_count(closure) == 1)
}
fn take_closure_env(&mut self) -> Option<Env> {
match std::mem::replace(&mut self.value, Value::Unit) {
Value::Closure(closure) => Rc::try_unwrap(closure).ok().map(|closure| closure.env),
_ => None,
}
}
}
#[derive(Default)]
struct ChainRelease {
closure_envs: Vec<Env>,
}
impl ChainRelease {
fn release_links_of(mut self, frame: &mut Frame) {
let mut link = self.next_link_of(frame);
loop {
link = match link.into_sole_frame() {
Some(mut linked) => self.next_link_of(&mut linked),
None => match self.closure_envs.pop() {
Some(env) => env,
None => return,
},
};
}
}
fn next_link_of(&mut self, frame: &mut Frame) -> Env {
if frame.owns_a_closure() {
self.closure_envs.extend(frame.take_closure_env());
}
std::mem::take(&mut frame.parent)
}
}
impl Env {
pub fn bind(&self, binding: BindingId, value: Value) -> Env {
Env(Some(Rc::new(Frame {
binding,
value,
parent: self.clone(),
})))
}
pub fn frame_count(&self) -> usize {
std::iter::successors(self.0.as_deref(), |frame| frame.parent.0.as_deref()).count()
}
fn is_sole_owner(&self) -> bool {
self.0
.as_ref()
.is_some_and(|frame| Rc::strong_count(frame) == 1)
}
fn is_a_sole_chain(&self) -> bool {
self.0
.as_ref()
.is_some_and(|frame| Rc::strong_count(frame) == 1 && frame.parent.is_sole_owner())
}
fn into_sole_frame(self) -> Option<Frame> {
self.0.and_then(|frame| Rc::try_unwrap(frame).ok())
}
pub fn lookup(&self, binding: BindingId) -> Option<&Value> {
let mut current = self.0.as_deref();
while let Some(frame) = current {
if frame.binding == binding {
return Some(&frame.value);
}
current = frame.parent.0.as_deref();
}
None
}
}
#[cfg(test)]
mod tests {
use std::rc::Rc;
use super::{Closure, Env, Value};
use crate::core::{BindingId, Lambda};
struct ChainFixture;
impl ChainFixture {
const LONG_CHAIN_LINKS: usize = 1_000_000;
fn binding() -> BindingId {
BindingId::from_index(0)
}
fn closure_over(env: Env) -> Rc<Closure> {
let lambda = Lambda::new(Vec::new(), Default::default());
Rc::new(Closure {
lambda: Rc::new(lambda),
env,
})
}
fn closure_chain(links: usize) -> Value {
(0..links).fold(Value::Unit, |previous, _| {
let env = Env::default().bind(Self::binding(), previous);
Value::Closure(Self::closure_over(env))
})
}
fn parent_chain(links: usize) -> Env {
(0..links).fold(Env::default(), |env, _| {
env.bind(Self::binding(), Value::Unit)
})
}
fn two_branches(links: usize) -> Env {
let closure = Value::Closure(Self::closure_over(Self::parent_chain(links)));
Self::parent_chain(links).bind(Self::binding(), closure)
}
}
#[test]
fn a_long_closure_chain_frees_without_recursion() {
drop(ChainFixture::closure_chain(ChainFixture::LONG_CHAIN_LINKS));
}
#[test]
fn a_long_parent_chain_frees_without_recursion() {
drop(ChainFixture::parent_chain(ChainFixture::LONG_CHAIN_LINKS));
}
#[test]
fn a_frame_with_two_long_branches_frees_without_recursion() {
drop(ChainFixture::two_branches(ChainFixture::LONG_CHAIN_LINKS));
}
#[test]
fn freeing_a_frame_keeps_a_closure_held_elsewhere() {
let kept = ChainFixture::closure_over(Env::default());
let env = Env::default().bind(ChainFixture::binding(), Value::Closure(Rc::clone(&kept)));
drop(env);
assert_eq!(Rc::strong_count(&kept), 1);
}
#[test]
fn freeing_a_frame_keeps_a_parent_held_elsewhere() {
let parent = Env::default().bind(ChainFixture::binding(), Value::Bool(true));
drop(parent.bind(ChainFixture::binding(), Value::Unit));
assert!(matches!(
parent.lookup(ChainFixture::binding()),
Some(Value::Bool(true))
));
}
#[test]
fn freeing_a_chain_frees_a_closure_it_owned() {
let held = ChainFixture::closure_over(Env::default());
let inner = Env::default().bind(ChainFixture::binding(), Value::Closure(Rc::clone(&held)));
let closure = ChainFixture::closure_over(inner);
drop(Env::default().bind(ChainFixture::binding(), Value::Closure(closure)));
assert_eq!(Rc::strong_count(&held), 1);
}
}