diff --git a/fix-runtime/src/machine.rs b/fix-runtime/src/machine.rs
index 93dc3cf..84194ee 100644
--- a/fix-runtime/src/machine.rs
+++ b/fix-runtime/src/machine.rs
@@ -75,6 +75,7 @@ pub trait Machine<'gc> {
             pc: ret_pc,
             thunk: _,
             env,
+            depth: None,
         }) = self.pop_call_frame()
         else {
             unreachable!()
diff --git a/fix-runtime/src/state.rs b/fix-runtime/src/state.rs
index 189bc4a..dba96d5 100644
--- a/fix-runtime/src/state.rs
+++ b/fix-runtime/src/state.rs
@@ -59,8 +59,9 @@ pub struct ErrorFrame {
 #[collect(no_drop)]
 pub struct CallFrame<'gc> {
     pub pc: usize,
-    pub thunk: Option<Gc<'gc, Thunk<'gc>>>,
     pub env: GcEnv<'gc>,
+    pub thunk: Option<Gc<'gc, Thunk<'gc>>>,
+    pub depth: Option<usize>,
 }
 
 #[derive(Debug)]
diff --git a/fix-runtime/src/value.rs b/fix-runtime/src/value.rs
index 7945ebb..61e5287 100644
--- a/fix-runtime/src/value.rs
+++ b/fix-runtime/src/value.rs
@@ -26,11 +26,11 @@ pub trait ValueVariant<'gc>: private::Cealed {
         private_bounds,
         reason = "Storable is a sealed implementation detail of the value system"
     )]
-    type Ty: Storable + 'gc;
+    type Ty: Storable<'gc>;
     const TYPE: NixType;
 }
 
-trait Storable: private::Cealed {
+trait Storable<'gc>: TryFrom<Value<'gc>> + Into<Value<'gc>> + private::Cealed + 'gc {
     fn is(raw: &RawBox) -> bool;
 
     fn to_raw_box(self) -> RawBox;
@@ -46,7 +46,7 @@ macro_rules! define_value_types {
         gc { $($gtype:ty => $gtag:path, $gty:path, $gname:literal;)* }
     ) => {
         $(
-        impl Storable for $itype {
+        impl Storable<'_> for $itype {
             #[inline(always)]
             fn is(value: &RawBox) -> bool {
                 value.tag() == Some($itag)
@@ -80,7 +80,7 @@ macro_rules! define_value_types {
         }
         )*
         $(
-        impl Storable for Gc<'_, $gtype> {
+        impl<'gc> Storable<'gc> for Gc<'gc, unelide_lifetimes!('gc; $gtype)> {
             #[inline(always)]
             fn is(value: &RawBox) -> bool {
                 value.tag() == Some($gtag)
@@ -202,7 +202,7 @@ define_value_types! {
 
 impl private::Cealed for f64 {}
 
-impl Storable for f64 {
+impl Storable<'_> for f64 {
     #[inline(always)]
     fn is(value: &RawBox) -> bool {
         value.is_float()
@@ -224,7 +224,14 @@ impl<'gc> ValueVariant<'gc> for f64 {
     const TYPE: NixType = NixType::Float;
 }
 
-impl<'gc, T: Storable + 'gc> From<T> for Value<'gc> {
+impl<'gc> TryFrom<Value<'gc>> for f64 {
+    type Error = ();
+    fn try_from(value: Value<'gc>) -> Result<Self, Self::Error> {
+        value.downcast::<f64>().ok_or(())
+    }
+}
+
+impl<'gc, T: Storable<'gc>> From<T> for Value<'gc> {
     fn from(value: T) -> Self {
         Value::new(value)
     }
@@ -260,7 +267,7 @@ impl<'gc> Value<'gc> {
         private_bounds,
         reason = "Storable is a sealed implementation detail of the value system"
     )]
-    pub fn new<T: Storable>(val: T) -> Self {
+    pub fn new<T: Storable<'gc>>(val: T) -> Self {
         Self {
             raw: val.to_raw_box(),
             _marker: PhantomData,
@@ -380,7 +387,7 @@ impl StaticValue {
         private_bounds,
         reason = "Storable is a sealed implementation detail of the value system"
     )]
-    pub fn new<T: Storable + 'static>(val: T) -> Self {
+    pub fn new<T: Storable<'static>>(val: T) -> Self {
         Self(Value::new(val))
     }
 
@@ -597,14 +604,6 @@ pub struct Env<'gc> {
 }
 pub type GcEnv<'gc> = GcRefLock<'gc, Env<'gc>>;
 
-#[derive(Collect, Debug)]
-#[collect(no_drop)]
-pub struct WithEnv<'gc> {
-    pub env: Value<'gc>,
-    pub prev: Option<GcWithEnv<'gc>>,
-}
-pub type GcWithEnv<'gc> = Gc<'gc, WithEnv<'gc>>;
-
 impl<'gc> Env<'gc> {
     pub fn empty() -> Self {
         Env {
@@ -722,6 +721,13 @@ impl<'gc> From<StrictValue<'gc>> for Value<'gc> {
     }
 }
 
+impl<'gc> TryFrom<Value<'gc>> for StrictValue<'gc> {
+    type Error = Gc<'gc, Thunk<'gc>>;
+    fn try_from(value: Value<'gc>) -> Result<Self, Self::Error> {
+        value.restrict()
+    }
+}
+
 impl fmt::Debug for StrictValue<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Debug::fmt(&self.0, f)
diff --git a/fix-vm/src/instructions/calls.rs b/fix-vm/src/instructions/calls.rs
index 3a67345..e4b009a 100644
--- a/fix-vm/src/instructions/calls.rs
+++ b/fix-vm/src/instructions/calls.rs
@@ -34,6 +34,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
                 pc: resume_pc,
                 thunk: None,
                 env: m.env(),
+                depth: None,
             });
             reader.set_pc(Continuation::CallPattern.ip() as usize);
             return Step::Continue(());
@@ -47,6 +48,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
             pc: resume_pc,
             thunk: None,
             env: m.env(),
+            depth: None,
         });
         reader.set_pc(ip as usize);
         m.set_env(new_env);
@@ -57,6 +59,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
                 pc: resume_pc,
                 thunk: None,
                 env: m.env(),
+                depth: None,
             });
             reader.set_pc(primop.dispatch_ip as usize)
         } else {
@@ -77,6 +80,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
                 pc: resume_pc,
                 thunk: None,
                 env: m.env(),
+                depth: None,
             });
             reader.set_pc(app.primop.dispatch_ip as usize)
         } else {
@@ -101,6 +105,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
             pc: resume_pc,
             thunk: None,
             env: m.env(),
+            depth: None,
         });
         m.push(arg);
         m.push(func.relax());
@@ -140,6 +145,7 @@ pub(crate) fn op_return<'gc, M: Machine<'gc>>(
         pc: ret_pc,
         thunk,
         env,
+        depth,
     }) = m.pop_call_frame()
     else {
         match m.force_mode() {
@@ -156,6 +162,7 @@ pub(crate) fn op_return<'gc, M: Machine<'gc>>(
                     pc: Continuation::ForceResultDeepFinish.ip() as usize,
                     thunk: None,
                     env: m.env(),
+                    depth: None,
                 });
                 m.inc_call_depth();
                 reader.set_pc(Continuation::PDeepSeq.ip() as usize);
@@ -166,6 +173,9 @@ pub(crate) fn op_return<'gc, M: Machine<'gc>>(
     reader.set_pc(ret_pc);
     if let Some(outer_thunk) = thunk {
         *outer_thunk.borrow_mut(mc) = ThunkState::Evaluated(val);
+        if let Some(depth) = depth {
+            m.replace(depth, val.relax());
+        }
     } else {
         m.dec_call_depth();
         m.push(val.relax())
diff --git a/fix-vm/src/instructions/with_scope.rs b/fix-vm/src/instructions/with_scope.rs
index 510785d..aac8eb4 100644
--- a/fix-vm/src/instructions/with_scope.rs
+++ b/fix-vm/src/instructions/with_scope.rs
@@ -41,6 +41,7 @@ pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
                         thunk: Some(thunk),
                         pc: resume_pc,
                         env: m.env(),
+                        depth: None,
                     });
                     m.set_env(env);
                     reader.set_pc(ip);
@@ -52,6 +53,7 @@ pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
                         thunk: Some(thunk),
                         pc: resume_pc,
                         env: m.env(),
+                        depth: None,
                     });
                     m.push(func);
                     return m.call(reader, mc, arg, resume_pc);
diff --git a/fix-vm/src/lib.rs b/fix-vm/src/lib.rs
index d105113..09524f7 100644
--- a/fix-vm/src/lib.rs
+++ b/fix-vm/src/lib.rs
@@ -211,6 +211,7 @@ impl<'gc> Machine<'gc> for Vm<'gc> {
                     thunk: Some(thunk),
                     pc: resume_pc,
                     env: self.env,
+                    depth: Some(depth),
                 });
                 self.env = env;
                 reader.set_pc(ip);
@@ -225,6 +226,7 @@ impl<'gc> Machine<'gc> for Vm<'gc> {
                     thunk: Some(thunk),
                     pc: resume_pc,
                     env: self.env,
+                    depth: Some(depth),
                 });
                 self.push(func);
                 self.call(reader, mc, arg, resume_pc)
diff --git a/fix-vm/src/primops/eq.rs b/fix-vm/src/primops/eq.rs
index 25ae70b..f87fbe5 100644
--- a/fix-vm/src/primops/eq.rs
+++ b/fix-vm/src/primops/eq.rs
@@ -166,6 +166,7 @@ fn enter_eq_machine<'gc, M: Machine<'gc>>(
         pc: resume_pc,
         thunk: None,
         env: m.env(),
+        depth: None,
     });
     m.inc_call_depth();
     m.push(Value::new(negate));
diff --git a/fix-vm/src/primops/io.rs b/fix-vm/src/primops/io.rs
index 40e58bc..2173167 100644
--- a/fix-vm/src/primops/io.rs
+++ b/fix-vm/src/primops/io.rs
@@ -46,6 +46,7 @@ pub fn import<'gc, M: Machine<'gc>>(
         pc: Continuation::PImportFinalize.ip() as usize,
         thunk: None,
         env,
+        depth: None,
     });
 
     m.set_pending_load(PendingLoad {
@@ -79,6 +80,7 @@ pub fn import_finalize<'gc, M: Machine<'gc>>(
         pc: ret_pc,
         thunk: _,
         env,
+        depth: None,
     }) = m.pop_call_frame()
     else {
         unreachable!()
@@ -120,6 +122,7 @@ pub fn scoped_import<'gc, M: Machine<'gc>>(
         pc: Continuation::PScopedImportFinalize.ip() as usize,
         thunk: None,
         env,
+        depth: None,
     });
 
     m.set_pending_load(PendingLoad {