Correctly halts

orchid-api/src/expr.rs

@@ -1,3 +1,4 @@
+use std::fmt;
 use std::num::NonZeroU64;
 
 use orchid_api_derive::{Coding, Hierarchy};
@@ -10,8 +11,13 @@ use crate::{Atom, ExtHostNotif, ExtHostReq, Location, OrcError, SysId, TStrv};
 /// [Acquire].
 ///
 /// The ID is globally unique within its lifetime, but may be reused.
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord, Coding)]
+#[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Coding)]
 pub struct ExprTicket(pub NonZeroU64);
+impl fmt::Debug for ExprTicket {
+	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+		write!(f, "ExprTicket({:x})", self.0.get())
+	}
+}
 
 /// Acquire a strong reference to an expression. This keeps it alive until a
 /// corresponding [Release] is emitted. The number of times a system has
@@ -62,7 +68,7 @@ pub enum ExpressionKind {
 	Arg(u64),
 	/// Insert the specified host-expression in the template here. When the clause
 	/// is used in the const tree, this variant is forbidden.
-	Slot(ExprTicket),
+	Slot { tk: ExprTicket, by_value: bool },
 	/// The lhs must be fully processed before the rhs can be processed.
 	/// Equivalent to Haskell's function of the same name
 	Seq(Box<Expression>, Box<Expression>),