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use std::borrow::Cow;
use std::rc::Rc;
use dhall_syntax::context::Context as SimpleContext;
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)]
pub(crate) enum CtxItem<T> {
Kept(AlphaVar, T),
Replaced(Thunk, T),
}
#[derive(Debug, Clone)]
pub(crate) struct Context<T>(Rc<SimpleContext<Label, CtxItem<T>>>);
#[derive(Debug, Clone)]
pub(crate) struct NormalizationContext(Context<()>);
#[derive(Debug, Clone)]
pub(crate) struct TypecheckContext(Context<Type>);
impl<T> CtxItem<T> {
fn forget(&self) -> CtxItem<()> {
match self {
CtxItem::Kept(var, _) => CtxItem::Kept(var.clone(), ()),
CtxItem::Replaced(e, _) => CtxItem::Replaced(e.clone(), ()),
}
}
}
impl<T> Context<T> {
pub(crate) fn new() -> Self {
Context(Rc::new(SimpleContext::new()))
}
pub(crate) fn forget(&self) -> Context<()> {
let mut ctx = SimpleContext::new();
for (k, vs) in self.0.iter_keys() {
for v in vs.iter() {
ctx = ctx.insert(k.clone(), v.forget());
}
}
Context(Rc::new(ctx))
}
pub(crate) fn insert_kept(&self, x: &Label, t: T) -> Self
where
T: Shift + Clone,
{
Context(Rc::new(self.0.map(|_, e| e.shift(1, &x.into())).insert(
x.clone(),
CtxItem::Kept(x.into(), t.shift(1, &x.into())),
)))
}
pub(crate) fn insert_replaced(&self, x: &Label, e: Thunk, t: T) -> Self
where
T: Clone,
{
Context(Rc::new(self.0.insert(x.clone(), CtxItem::Replaced(e, t))))
}
pub(crate) fn lookup(&self, var: &V<Label>) -> Option<&CtxItem<T>> {
let V(x, n) = var;
self.0.lookup(x, *n)
}
}
impl NormalizationContext {
pub(crate) fn new() -> Self {
NormalizationContext(Context::new())
}
pub(crate) fn skip(&self, x: &Label) -> Self {
NormalizationContext(self.0.insert_kept(x, ()))
}
pub(crate) fn lookup(&self, var: &V<Label>) -> Value {
match self.0.lookup(var) {
Some(CtxItem::Replaced(t, ())) => t.to_value(),
Some(CtxItem::Kept(newvar, ())) => Value::Var(newvar.clone()),
// Free variable
None => Value::Var(AlphaVar::from_var(var.clone())),
}
}
}
impl TypecheckContext {
pub(crate) fn new() -> Self {
TypecheckContext(Context::new())
}
pub(crate) fn insert_type(&self, x: &Label, t: Type) -> Self {
TypecheckContext(self.0.insert_kept(x, t))
}
pub(crate) 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(crate) fn lookup(&self, var: &V<Label>) -> Option<Cow<'_, Type>> {
match self.0.lookup(var) {
Some(CtxItem::Kept(_, t)) => Some(Cow::Borrowed(&t)),
Some(CtxItem::Replaced(_, t)) => Some(Cow::Borrowed(&t)),
None => None,
}
}
pub(crate) fn to_normalization_ctx(&self) -> NormalizationContext {
NormalizationContext(self.0.forget())
}
}
impl<T: Shift> Shift for CtxItem<T> {
fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
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: Shift> Shift for Context<T> {
fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
Context(Rc::new(self.0.map(|_, e| e.shift(delta, var))))
}
}
impl Shift for NormalizationContext {
fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
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) if v == var => {
CtxItem::Replaced(val.to_thunk(), t.subst_shift(var, val))
}
CtxItem::Kept(v, t) => {
CtxItem::Kept(v.shift(-1, var), t.subst_shift(var, val))
}
}
}
}
impl<T: Subst<Typed>> Subst<Typed> for Context<T> {
fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
Context(Rc::new(self.0.map(|_, e| e.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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