base and extension fully compiles, host in good shape

orchid-host/src/expr_store.rs

@@ -0,0 +1,35 @@
+use std::cell::RefCell;
+use std::fmt;
+
+use hashbrown::HashMap;
+use hashbrown::hash_map::Entry;
+
+use crate::api;
+use crate::expr::Expr;
+
+#[derive(Default)]
+pub struct ExprStore(RefCell<HashMap<api::ExprTicket, (u32, Expr)>>);
+impl ExprStore {
+	pub fn give_expr(&self, expr: Expr) {
+		match self.0.borrow_mut().entry(expr.id()) {
+			Entry::Occupied(mut oe) => oe.get_mut().0 += 1,
+			Entry::Vacant(v) => {
+				v.insert((1, expr));
+			},
+		}
+	}
+	pub fn take_expr(&self, ticket: api::ExprTicket) {
+		(self.0.borrow_mut().entry(ticket))
+			.and_replace_entry_with(|_, (rc, rt)| (1 < rc).then_some((rc - 1, rt)));
+	}
+	pub fn get_expr(&self, ticket: api::ExprTicket) -> Option<Expr> {
+		self.0.borrow().get(&ticket).map(|(_, expr)| expr.clone())
+	}
+}
+impl fmt::Display for ExprStore {
+	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+		let r = self.0.borrow();
+		let rc: u32 = r.values().map(|v| v.0).sum();
+		write!(f, "Store holding {rc} refs to {} exprs", r.len())
+	}
+}