diff --git a/fix-builtins/src/lib.rs b/fix-builtins/src/lib.rs
index 8d649ba..7ada8c2 100644
--- a/fix-builtins/src/lib.rs
+++ b/fix-builtins/src/lib.rs
@@ -171,6 +171,10 @@ pub enum PrimOpPhase {
     FindFile,
     Floor,
     FoldlStrict,
+    FoldlStrictEmpty,
+    FoldlStrictCall1,
+    FoldlStrictCall2,
+    FoldlStrictUpdate,
     FromJSON,
     FromTOML,
     FunctionArgs,
diff --git a/fix-vm/src/instructions/misc.rs b/fix-vm/src/instructions/misc.rs
index 59895b8..4bb6a55 100644
--- a/fix-vm/src/instructions/misc.rs
+++ b/fix-vm/src/instructions/misc.rs
@@ -51,9 +51,7 @@ impl<'gc> crate::Vm<'gc> {
             }
         };
         let Some(attrs) = scope.as_gc::<AttrSet>() else {
-            return self.finish_err(Error::eval_error(
-                "internal: scope slot is not an attrset",
-            ));
+            return self.finish_err(Error::eval_error("internal: scope slot is not an attrset"));
         };
         match attrs.lookup(name) {
             Some(val) => {
@@ -152,8 +150,8 @@ fn resolve_path_str(current_dir: &str, path: &str) -> Result<String, Box<Error>>
         return Ok(path.to_owned());
     } else if let Some(rest) = path.strip_prefix("~/") {
         #[allow(deprecated)]
-        let mut dir = std::env::home_dir()
-            .ok_or_else(|| Error::eval_error("home dir not defined"))?;
+        let mut dir =
+            std::env::home_dir().ok_or_else(|| Error::eval_error("home dir not defined"))?;
         dir.push(rest);
         dir
     } else {
diff --git a/fix-vm/src/primops/list.rs b/fix-vm/src/primops/list.rs
index ce1eb45..ca17b6b 100644
--- a/fix-vm/src/primops/list.rs
+++ b/fix-vm/src/primops/list.rs
@@ -70,4 +70,100 @@ impl<'gc> Vm<'gc> {
         reader.set_pc(PrimOpPhase::FilterCallPred.ip() as usize);
         Step::Continue(())
     }
+
+    // foldl' op nul list
+    //
+    // Stack layouts across phases:
+    //   Entry:  [op, nul, list]
+    //   Empty:  [op, nul]
+    //   Call1:  [op, list, idx, acc]
+    //   Call2:  [op, list, idx, acc, intermediate]
+    //   Update: [op, list, idx, acc, result]
+    pub(crate) fn primop_foldl_strict_entry(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.force_slot(0, reader, mc)?;
+        let list_val = self.peek_forced(0);
+        let Some(list) = list_val.as_gc::<List>() else {
+            return self.finish_type_err(NixType::List, list_val.ty());
+        };
+        if list.inner.borrow().is_empty() {
+            let _ = self.pop(); // list
+            reader.set_pc(PrimOpPhase::FoldlStrictEmpty.ip() as usize);
+            return Step::Continue(());
+        }
+        let list_val = self.pop();
+        let nul_val = self.pop();
+        self.push(list_val);
+        self.push(Value::new_inline(0i32));
+        self.push(nul_val);
+        reader.set_pc(PrimOpPhase::FoldlStrictCall1.ip() as usize);
+        Step::Continue(())
+    }
+
+    pub(crate) fn primop_foldl_strict_empty(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let nul = self.force_and_retry::<StrictValue>(reader, mc)?;
+        let _ = self.pop(); // op
+        self.return_from_primop(nul.relax(), reader)
+    }
+
+    pub(crate) fn primop_foldl_strict_call1(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.force_slot(3, reader, mc)?;
+        let op = self.peek_forced(3);
+        let acc = self.peek(0);
+        self.push(op.relax());
+        self.call(reader, mc, acc, PrimOpPhase::FoldlStrictCall2.ip() as usize)
+    }
+
+    pub(crate) fn primop_foldl_strict_call2(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        #[allow(clippy::unwrap_used)]
+        let idx = self.peek(2).as_inline::<i32>().unwrap();
+        #[allow(clippy::unwrap_used)]
+        let list = self.peek_forced(3).as_gc::<List>().unwrap();
+        let elem = list.inner.borrow()[idx as usize];
+        self.call(
+            reader,
+            mc,
+            elem,
+            PrimOpPhase::FoldlStrictUpdate.ip() as usize,
+        )
+    }
+
+    pub(crate) fn primop_foldl_strict_update(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        _mc: &Mutation<'gc>,
+    ) -> Step {
+        let result = self.pop();
+        self.replace(0, result);
+        #[allow(clippy::unwrap_used)]
+        let idx = self.peek(1).as_inline::<i32>().unwrap();
+        #[allow(clippy::unwrap_used)]
+        let list = self.peek_forced(2).as_gc::<List>().unwrap();
+        let len = list.inner.borrow().len();
+        if (idx as usize) + 1 == len {
+            let acc = self.pop();
+            let _ = self.pop(); // idx
+            let _ = self.pop(); // list
+            let _ = self.pop(); // op
+            return self.return_from_primop(acc, reader);
+        }
+        self.replace(1, Value::new_inline(idx + 1));
+        reader.set_pc(PrimOpPhase::FoldlStrictCall1.ip() as usize);
+        Step::Continue(())
+    }
 }
diff --git a/fix-vm/src/primops/mod.rs b/fix-vm/src/primops/mod.rs
index a0689d8..90e7cf0 100644
--- a/fix-vm/src/primops/mod.rs
+++ b/fix-vm/src/primops/mod.rs
@@ -41,6 +41,12 @@ impl<'gc> Vm<'gc> {
             FilterCallPred => self.primop_filter_call_pred(reader, mc),
             FilterCheck => self.primop_filter_check(reader, mc),
 
+            FoldlStrict => self.primop_foldl_strict_entry(reader, mc),
+            FoldlStrictEmpty => self.primop_foldl_strict_empty(reader, mc),
+            FoldlStrictCall1 => self.primop_foldl_strict_call1(reader, mc),
+            FoldlStrictCall2 => self.primop_foldl_strict_call2(reader, mc),
+            FoldlStrictUpdate => self.primop_foldl_strict_update(reader, mc),
+
             ForceResultShallow => self.primop_force_result_shallow(ctx, reader, mc),
             ForceResultShallowPush => self.primop_force_result_shallow_push(ctx, reader, mc),
             ForceResultShallowLoop => self.primop_force_result_shallow_loop(reader, mc),
diff --git a/fix/src/lib.rs b/fix/src/lib.rs
index 80cb3a5..42ea6af 100644
--- a/fix/src/lib.rs
+++ b/fix/src/lib.rs
@@ -636,7 +636,10 @@ enum Scope<'ctx, 'id, 'ir> {
         slot_id: u32,
     },
     Let(HashMap<StringId, GhostMaybeThunkRef<'id, 'ir>>),
-    Param { sym: StringId, abs_layer: u8 },
+    Param {
+        sym: StringId,
+        abs_layer: u8,
+    },
 }
 
 pub enum ExtraScope<'ctx> {