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use std::cell::RefCell;
use std::collections::HashMap;
use std::rc::Rc;
use crate::error::TypeError;
use crate::semantics::core::value::Value;
use crate::semantics::core::value::ValueKind;
use crate::semantics::core::var::{AlphaVar, Binder, Shift, Subst};
use crate::syntax::{Label, V};
#[derive(Debug, Clone)]
enum CtxItem {
Kept(AlphaVar, Value),
Replaced(Value),
}
#[derive(Debug, Clone)]
pub(crate) struct TyCtx {
ctx: Vec<(Binder, CtxItem)>,
/// Keeps track of the next free binder id to assign. Shared among all the contexts to ensure
/// unicity across the expression.
next_uid: Rc<RefCell<u64>>,
}
impl TyCtx {
pub fn new() -> Self {
TyCtx {
ctx: Vec::new(),
next_uid: Rc::new(RefCell::new(0)),
}
}
fn with_vec(&self, vec: Vec<(Binder, CtxItem)>) -> Self {
TyCtx {
ctx: vec,
next_uid: self.next_uid.clone(),
}
}
pub fn insert_type(&self, x: &Binder, t: Value) -> Self {
let mut vec = self.ctx.clone();
vec.push((x.clone(), CtxItem::Kept(x.into(), t.under_binder(x))));
self.with_vec(vec)
}
pub fn insert_value(
&self,
x: &Binder,
e: Value,
) -> Result<Self, TypeError> {
let mut vec = self.ctx.clone();
vec.push((x.clone(), CtxItem::Replaced(e)));
Ok(self.with_vec(vec))
}
pub fn lookup(&self, var: &V<Label>) -> Option<Value> {
let mut var = var.clone();
let mut shift_map: HashMap<Label, _> = HashMap::new();
for (b, i) in self.ctx.iter().rev() {
let l = b.to_label();
match var.over_binder(&l) {
None => {
let i = i.under_multiple_binders(&shift_map);
return Some(match i {
CtxItem::Kept(newvar, t) => {
Value::from_kind_and_type(ValueKind::Var(newvar), t)
}
CtxItem::Replaced(v) => v,
});
}
Some(newvar) => var = newvar,
};
if let CtxItem::Kept(_, _) = i {
*shift_map.entry(l).or_insert(0) += 1;
}
}
// Unbound variable
None
}
pub fn new_binder(&self, l: &Label) -> Binder {
let mut next_uid = self.next_uid.borrow_mut();
let uid = *next_uid;
*next_uid += 1;
Binder::new(l.clone(), uid)
}
/// 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) -> Result<CtxItem, E>,
) -> Result<Self, E> {
let mut vec = Vec::new();
vec.reserve(self.ctx.len());
let mut var = var.clone();
let mut iter = self.ctx.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(self.with_vec(vec))
}
fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
if delta < 0 {
Some(self.do_with_var(var, |var, i| Ok(i.shift(delta, &var)?))?)
} else {
Some(
self.with_vec(
self.ctx
.iter()
.map(|(l, i)| Ok((l.clone(), i.shift(delta, &var)?)))
.collect::<Result<_, _>>()?,
),
)
}
}
fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self {
self.do_with_var(var, |var, i| Ok::<_, !>(i.subst_shift(&var, val)))
.unwrap()
}
}
impl Shift for CtxItem {
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) => CtxItem::Replaced(e.shift(delta, var)?),
})
}
}
impl Shift for TyCtx {
fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
self.shift(delta, var)
}
}
impl Subst<Value> for CtxItem {
fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self {
match self {
CtxItem::Replaced(e) => CtxItem::Replaced(e.subst_shift(var, val)),
CtxItem::Kept(v, t) => match v.shift(-1, var) {
None => CtxItem::Replaced(val.clone()),
Some(newvar) => CtxItem::Kept(newvar, t.subst_shift(var, val)),
},
}
}
}
impl Subst<Value> for TyCtx {
fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self {
self.subst_shift(var, val)
}
}
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