diff --git a/components/milkshake/src/python/milkshake/__init__.py b/components/milkshake/src/python/milkshake/__init__.py
index 3aa544d..b0828f3 100644
--- a/components/milkshake/src/python/milkshake/__init__.py
+++ b/components/milkshake/src/python/milkshake/__init__.py
@@ -3,7 +3,7 @@
 
 from importlib.resources import files
 
-from attrs import define, field
+from attrs import define
 from lark import Lark, Tree, Token, Transformer, v_args
 
 
@@ -11,7 +11,7 @@ with files(__package__).joinpath("grammar.lark").open("r", encoding="utf-8") as
     GRAMMAR = fp.read()
 
 
-@define
+@define(frozen=True)
 class Symbol:
     name: str
 
diff --git a/components/typhon/src/python/typhon/evaluator.py b/components/typhon/src/python/typhon/evaluator.py
index 1e04309..e31f4d7 100644
--- a/components/typhon/src/python/typhon/evaluator.py
+++ b/components/typhon/src/python/typhon/evaluator.py
@@ -8,6 +8,8 @@ to implement a flat, stackless, serializable interpreter.
 
 import typing as t
 
+from milkshake import Symbol
+
 from .models import *
 from .util import *
 
@@ -18,24 +20,24 @@ class Operator:
     """Stack operators."""
 
 
-class Task:
+class Op:
     @attrs.define()
     class Complete:
         """Signals program termination."""
 
-        pass
+    @attrs.define()
+    class Drop:
+        """Drop or void the top of the data stack."""
 
     @attrs.define()
     class Eval:
         """Evaluate the current term."""
 
-        pass
-
     @attrs.define()
-    class Apply:
-        """Apply an operator to the stack."""
+    class Invoke:
+        """Consuming the top N items of the stack of the format [... <fn>, <... args>] invoke fn with args."""
 
-        operator: "Operator" = attrs.field()
+        n: int
 
     @attrs.define()
     class Next:
@@ -67,19 +69,64 @@ def step(vm: Vm, cont: Cont, frame: Frame):
 
     """
 
+    if frame.op_stack:
+        expr = frame.op_stack.pop()
+
+    else:
+        expr = get_in(vm.log, frame.pc)
+
     match expr:
-        case ["native", native_fn, arg_exprs, vararg_expr]:
+        # AST entries
+        case ["py", native_expr, arg_exprs, vararg_expr]:
             pass
 
-        case ["invoke", fn_expr, arg_exprs, vararg_expr]:
+        case ["lambda", arg_expr, body_expr]:
+            # "now this one;s hard"
             pass
 
-        case ["var", name]:
+        case ["do", *body_exprs]:
             pass
 
-        case int() | float() | str() | bool():
+        case ["if", test_expr, then_expr, else_expr]:
             pass
 
+        case ["if", test_expr, then_expr]:
+            pass
+
+        # Generalized "simple" invoke expression
+        case [fn_expr, *arg_exprs]:
+            pass
+
+        # Literals/terminals
+        case Symbol(name):
+            # Resolve a value from the scope(s)
+            for frame in reversed(cont.frames):
+                if name in frame.frame_ns:
+                    frame.data_stack.append(frame.frame_ns[name])
+                    break
+            else:
+                raise NameError(f"{name!r} is not bound")
+
+        case int() | float() | str() | bool() | dict() | set():
+            # Literals push
+            frame.data_stack.append(expr)
+
+        # Semi-VM instructions
+        case Op.Drop():
+            frame.data_stack.pop()
+
+        case Op.Invoke(n):
+            data = [frame.data_stack.pop() for _ in range(n)]
+            fn = data[-1]
+            args = data[-1::]
+
+            # Need to trampoline the call through the wrapping loop
+            return Op.Frame(fn, args)
+
+        # FIXME: Do we still need this?
+        case Op.Complete():
+            return expr
+
 
 def run(program, state=None):
     vm = state or Vm([], {}, [])
diff --git a/components/typhon/src/python/typhon/models.py b/components/typhon/src/python/typhon/models.py
index f334909..8371a11 100644
--- a/components/typhon/src/python/typhon/models.py
+++ b/components/typhon/src/python/typhon/models.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 
+from collections import deque
 import typing as t
 
 import attrs
@@ -40,5 +41,5 @@ class Frame:
 
     pc: list = attrs.field(factory=lambda: [0])
     frame_ns: dict = attrs.field(factory=dict)
-    op_stack: list = attrs.field(factory=list)
-    data_stack: list = attrs.field(factory=list)
+    op_stack: deque = attrs.field(factory=deque)
+    data_stack: deque = attrs.field(factory=deque)