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use std::collections::HashMap;
use std::rc::Rc;
use dhall_syntax::{Label, V};
use crate::core::thunk::Thunk;
use crate::core::value::Value;
use crate::core::var::{AlphaVar, Shift, Subst};
use crate::error::TypeError;
use crate::phase::{Type, Typed};
#[derive(Debug, Clone)]
enum CtxItem<T> {
Kept(AlphaVar, T),
Replaced(Thunk, T),
}
#[derive(Debug, Clone)]
struct Context<T>(Rc<Vec<(Label, CtxItem<T>)>>);
#[derive(Debug, Clone)]
pub(crate) struct NormalizationContext(Context<()>);
#[derive(Debug, Clone)]
pub(crate) struct TypecheckContext(Context<Type>);
impl<T> Context<T> {
pub fn new() -> Self {
Context(Rc::new(Vec::new()))
}
pub fn insert_kept(&self, x: &Label, t: T) -> Self
where
T: Shift + Clone,
{
let mut vec = self.0.as_ref().clone();
vec.push((x.clone(), CtxItem::Kept(x.into(), t.under_binder(x))));
Context(Rc::new(vec))
}
pub fn insert_replaced(&self, x: &Label, th: Thunk, t: T) -> Self
where
T: Clone,
{
let mut vec = self.0.as_ref().clone();
vec.push((x.clone(), CtxItem::Replaced(th, t)));
Context(Rc::new(vec))
}
pub fn lookup(&self, var: &V<Label>) -> Result<CtxItem<T>, V<Label>>
where
T: Clone + Shift,
{
let mut var = var.clone();
let mut shift_map: HashMap<Label, _> = HashMap::new();
for (l, i) in self.0.iter().rev() {
match var.over_binder(l) {
None => return Ok(i.under_multiple_binders(&shift_map)),
Some(newvar) => var = newvar,
};
if let CtxItem::Kept(_, _) = i {
*shift_map.entry(l.clone()).or_insert(0) += 1;
}
}
// Free variable
Err(var)
}
/// Given a var that makes sense in the current context, map the given function in such a way
/// that the passed variable always makes sense in the context of the passed item.
/// Once we pass the variable definition, the variable doesn't make sense anymore so we just
/// copy the remaining items.
fn do_with_var<E>(
&self,
var: &AlphaVar,
mut f: impl FnMut(&AlphaVar, &CtxItem<T>) -> Result<CtxItem<T>, E>,
) -> Result<Self, E>
where
T: Clone,
{
let mut vec = Vec::new();
vec.reserve(self.0.len());
let mut var = var.clone();
let mut iter = self.0.iter().rev();
for (l, i) in iter.by_ref() {
vec.push((l.clone(), f(&var, i)?));
if let CtxItem::Kept(_, _) = i {
match var.over_binder(l) {
None => break,
Some(newvar) => var = newvar,
};
}
}
for (l, i) in iter {
vec.push((l.clone(), (*i).clone()));
}
vec.reverse();
Ok(Context(Rc::new(vec)))
}
fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self>
where
T: Clone + Shift,
{
if delta < 0 {
Some(self.do_with_var(var, |var, i| Ok(i.shift(delta, &var)?))?)
} else {
Some(Context(Rc::new(
self.0
.iter()
.map(|(l, i)| Ok((l.clone(), i.shift(delta, &var)?)))
.collect::<Result<_, _>>()?,
)))
}
}
fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self
where
T: Clone + Subst<Typed>,
{
self.do_with_var(var, |var, i| Ok::<_, !>(i.subst_shift(&var, val)))
.unwrap()
}
}
impl NormalizationContext {
pub fn new() -> Self {
NormalizationContext(Context::new())
}
pub fn skip(&self, x: &Label) -> Self {
NormalizationContext(self.0.insert_kept(x, ()))
}
pub fn lookup(&self, var: &V<Label>) -> Value {
match self.0.lookup(var) {
Ok(CtxItem::Replaced(t, ())) => t.to_value(),
Ok(CtxItem::Kept(newvar, ())) => Value::Var(newvar.clone()),
Err(var) => Value::Var(AlphaVar::from_var(var)),
}
}
}
impl TypecheckContext {
pub fn new() -> Self {
TypecheckContext(Context::new())
}
pub fn insert_type(&self, x: &Label, t: Type) -> Self {
TypecheckContext(self.0.insert_kept(x, t))
}
pub fn insert_value(&self, x: &Label, e: Typed) -> Result<Self, TypeError> {
Ok(TypecheckContext(self.0.insert_replaced(
x,
e.to_thunk(),
e.get_type()?.into_owned(),
)))
}
pub fn lookup(&self, var: &V<Label>) -> Option<Typed> {
match self.0.lookup(var) {
Ok(CtxItem::Kept(newvar, t)) => Some(Typed::from_thunk_and_type(
Thunk::from_value(Value::Var(newvar.clone())),
t.clone(),
)),
Ok(CtxItem::Replaced(th, t)) => {
Some(Typed::from_thunk_and_type(th.clone(), t.clone()))
}
Err(_) => None,
}
}
}
impl<T: Shift> Shift for CtxItem<T> {
fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
Some(match self {
CtxItem::Kept(v, t) => {
CtxItem::Kept(v.shift(delta, var)?, t.shift(delta, var)?)
}
CtxItem::Replaced(e, t) => {
CtxItem::Replaced(e.shift(delta, var)?, t.shift(delta, var)?)
}
})
}
}
impl<T: Clone + Shift> Shift for Context<T> {
fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
self.shift(delta, var)
}
}
impl Shift for NormalizationContext {
fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
Some(NormalizationContext(self.0.shift(delta, var)?))
}
}
impl<T: Subst<Typed>> Subst<Typed> for CtxItem<T> {
fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
match self {
CtxItem::Replaced(e, t) => CtxItem::Replaced(
e.subst_shift(var, val),
t.subst_shift(var, val),
),
CtxItem::Kept(v, t) => match v.shift(-1, var) {
None => {
CtxItem::Replaced(val.to_thunk(), t.subst_shift(var, val))
}
Some(newvar) => CtxItem::Kept(newvar, t.subst_shift(var, val)),
},
}
}
}
impl<T: Clone + Subst<Typed>> Subst<Typed> for Context<T> {
fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
self.subst_shift(var, val)
}
}
impl Subst<Typed> for NormalizationContext {
fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
NormalizationContext(self.0.subst_shift(var, val))
}
}
impl PartialEq for TypecheckContext {
fn eq(&self, _: &Self) -> bool {
// don't count contexts when comparing stuff
// this is dirty but needed for now
true
}
}
impl Eq for TypecheckContext {}
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