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use crate::semantics::{AlphaVar, Nir, NirKind};
use crate::Ctxt;
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum NzVar {
/// Reverse-debruijn index: counts number of binders from the bottom of the stack.
Bound(usize),
/// Fake fresh variable generated for expression equality checking.
Fresh(usize),
}
#[derive(Debug, Clone)]
enum EnvItem<'cx, T> {
// Variable is bound with given type
Kept(T),
// Variable has been replaced by corresponding value
Replaced(Nir<'cx>, T),
}
#[derive(Debug, Clone)]
pub struct ValEnv<'cx, T> {
cx: Ctxt<'cx>,
items: Vec<EnvItem<'cx, T>>,
}
pub type NzEnv<'cx> = ValEnv<'cx, ()>;
impl NzVar {
pub fn new(idx: usize) -> Self {
NzVar::Bound(idx)
}
pub fn fresh() -> Self {
use std::sync::atomic::{AtomicUsize, Ordering};
// Global counter to ensure uniqueness of the generated id.
static FRESH_VAR_COUNTER: AtomicUsize = AtomicUsize::new(0);
let id = FRESH_VAR_COUNTER.fetch_add(1, Ordering::SeqCst);
NzVar::Fresh(id)
}
/// Get index of bound variable.
/// Panics on a fresh variable.
pub fn idx(&self) -> usize {
match self {
NzVar::Bound(i) => *i,
NzVar::Fresh(_) => panic!(
"Trying to use a fresh variable outside of equality checking"
),
}
}
}
impl<'cx, T: Clone> ValEnv<'cx, T> {
pub fn new(cx: Ctxt<'cx>) -> Self {
ValEnv {
cx,
items: Vec::new(),
}
}
pub fn cx(&self) -> Ctxt<'cx> {
self.cx
}
pub fn discard_types(&self) -> ValEnv<'cx, ()> {
let items = self
.items
.iter()
.map(|i| match i {
EnvItem::Kept(_) => EnvItem::Kept(()),
EnvItem::Replaced(val, _) => EnvItem::Replaced(val.clone(), ()),
})
.collect();
ValEnv { cx: self.cx, items }
}
pub fn insert_type(&self, ty: T) -> Self {
let mut env = self.clone();
env.items.push(EnvItem::Kept(ty));
env
}
pub fn insert_value(&self, e: Nir<'cx>, ty: T) -> Self {
let mut env = self.clone();
env.items.push(EnvItem::Replaced(e, ty));
env
}
pub fn lookup_val(&self, var: AlphaVar) -> NirKind<'cx> {
let idx = self.items.len() - 1 - var.idx();
match &self.items[idx] {
EnvItem::Kept(_) => NirKind::Var(NzVar::new(idx)),
EnvItem::Replaced(x, _) => x.kind().clone(),
}
}
pub fn lookup_ty(&self, var: AlphaVar) -> T {
let idx = self.items.len() - 1 - var.idx();
match &self.items[idx] {
EnvItem::Kept(ty) | EnvItem::Replaced(_, ty) => ty.clone(),
}
}
}
impl<'cx, 'a> From<&'a NzEnv<'cx>> for NzEnv<'cx> {
fn from(x: &'a NzEnv<'cx>) -> Self {
x.clone()
}
}
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