diff --git a/include/bolt/Evaluator.hpp b/include/bolt/Evaluator.hpp
new file mode 100644
index 000000000..ae5127951
--- /dev/null
+++ b/include/bolt/Evaluator.hpp
@@ -0,0 +1,187 @@
+
+#pragma once
+
+#include <unordered_map>
+#include <functional>
+
+#include "bolt/ByteString.hpp"
+#include "bolt/CST.hpp"
+
+namespace bolt {
+
+  enum class ValueKind {
+    Empty,
+    String,
+    Integer,
+    Tuple,
+    SourceFunction,
+    NativeFunction,
+  };
+
+  class Value {
+
+    using NativeFunction = std::function<Value(std::vector<Value>)>;
+
+    using Tuple = std::vector<Value>;
+
+    ValueKind Kind;
+
+    union {
+      ByteString S;
+      Integer I;
+      LetDeclaration* D;
+      NativeFunction F;
+      Tuple T;
+    };
+
+  public:
+
+    Value():
+      Kind(ValueKind::Empty) {}
+
+    Value(ByteString S):
+      Kind(ValueKind::String), S(S) {}
+
+    Value(Integer I):
+      Kind(ValueKind::Integer), I(I) {}
+
+    Value(LetDeclaration* D):
+      Kind(ValueKind::SourceFunction), D(D) {}
+
+    Value(NativeFunction F):
+      Kind(ValueKind::NativeFunction), F(F) {}
+
+    Value(std::vector<Value> T):
+      Kind(ValueKind::Tuple), T(T) {}
+
+    Value(const Value& V):
+      Kind(V.Kind) {
+        switch (Kind) {
+          case ValueKind::String:
+            new (&S) ByteString(V.S);
+            break;
+          case ValueKind::Integer:
+            new (&I) Integer(V.I);
+            break;
+          case ValueKind::Tuple:
+            new (&I) Tuple(V.T);
+            break;
+          case ValueKind::SourceFunction:
+            new (&D) LetDeclaration*(V.D);
+            break;
+          case ValueKind::NativeFunction:
+            new (&F) NativeFunction(V.F);
+            break;
+          case ValueKind::Empty:
+            break;
+        }
+      }
+
+    Value& operator=(const Value& Other) noexcept {
+      Kind = Other.Kind;
+      switch (Kind) {
+        case ValueKind::String:
+          new (&S) ByteString(Other.S);
+          break;
+        case ValueKind::Integer:
+          new (&I) Integer(Other.I);
+          break;
+        case ValueKind::Tuple:
+          new (&I) Tuple(Other.T);
+          break;
+        case ValueKind::SourceFunction:
+          new (&D) LetDeclaration*(Other.D);
+          break;
+        case ValueKind::NativeFunction:
+          new (&F) NativeFunction(Other.F);
+          break;
+        case ValueKind::Empty:
+          break;
+      }
+      return *this;
+    }
+
+    // Add move constructor and move assignment methods
+
+    inline ValueKind getKind() const noexcept {
+      return Kind;
+    }
+
+    inline ByteString& asString() {
+      ZEN_ASSERT(Kind == ValueKind::String);
+      return S;
+    }
+
+    inline LetDeclaration* getDeclaration() {
+      ZEN_ASSERT(Kind == ValueKind::SourceFunction);
+      return D;
+    }
+
+    inline NativeFunction getBinding() {
+      ZEN_ASSERT(Kind == ValueKind::NativeFunction);
+      return F;
+    }
+
+    static Value binding(NativeFunction F) {
+      return Value(F);
+    }
+
+    static Value unit() {
+      return Value(Tuple {});
+    }
+
+    ~Value() {
+      switch (Kind) {
+        case ValueKind::String:
+          S.~ByteString();
+          break;
+        case ValueKind::Integer:
+          I.~Integer();
+          break;
+        case ValueKind::Tuple:
+          T.~Tuple();
+          break;
+        case ValueKind::SourceFunction:
+          break;
+        case ValueKind::NativeFunction:
+          F.~NativeFunction();
+          break;
+        case ValueKind::Empty:
+          break;
+      }
+    }
+
+  };
+
+  class Env {
+
+    std::unordered_map<ByteString, Value> Bindings;
+
+  public:
+
+    void add(const ByteString& Name, Value V) {
+      Bindings.emplace(Name, V);
+    }
+
+    Value& lookup(const ByteString& Name) {
+      auto Match = Bindings.find(Name);
+      ZEN_ASSERT(Match != Bindings.end());
+      return Match->second;
+    }
+
+  };
+
+  class Evaluator {
+
+  public:
+
+    void assignPattern(Pattern* P, Value& V, Env& E);
+
+    Value apply(Value Op, std::vector<Value> Args);
+
+    Value evaluateExpression(Expression* N, Env& E);
+
+    void evaluate(Node* N, Env& E);
+
+  };
+}
diff --git a/src/Evaluator.cc b/src/Evaluator.cc
new file mode 100644
index 000000000..3ceffb252
--- /dev/null
+++ b/src/Evaluator.cc
@@ -0,0 +1,127 @@
+
+#include "zen/range.hpp"
+
+#include "bolt/CST.hpp"
+#include "bolt/Evaluator.hpp"
+
+namespace bolt {
+
+  Value Evaluator::evaluateExpression(Expression* X, Env& E) {
+    switch (X->getKind()) {
+      case NodeKind::ReferenceExpression:
+      {
+        auto RE = static_cast<ReferenceExpression*>(X);
+        return E.lookup(RE->Name->getCanonicalText());
+        // auto Decl = RE->getScope()->lookup(RE->getSymbolPath());
+        // ZEN_ASSERT(Decl && Decl->getKind() == NodeKind::FunctionDeclaration);
+        // return static_cast<FunctionDeclaration*>(Decl);
+      }
+      case NodeKind::ConstantExpression:
+      {
+        auto CE = static_cast<ConstantExpression*>(X);
+        switch (CE->Token->getKind()) {
+          case NodeKind::IntegerLiteral:
+            return static_cast<IntegerLiteral*>(CE->Token)->V;
+          case NodeKind::StringLiteral:
+            return static_cast<StringLiteral*>(CE->Token)->Text;
+          default:
+            ZEN_UNREACHABLE
+        }
+      }
+      case NodeKind::CallExpression:
+      {
+        auto CE = static_cast<CallExpression*>(X);
+        auto Op = evaluateExpression(CE->Function, E);
+        std::vector<Value> Args;
+        for (auto Arg: CE->Args) {
+          Args.push_back(evaluateExpression(Arg, E));
+        }
+        return apply(Op, Args);
+      }
+      default:
+        ZEN_UNREACHABLE
+    }
+  }
+
+  void Evaluator::assignPattern(Pattern* P, Value& V, Env& E) {
+    switch (P->getKind()) {
+      case NodeKind::BindPattern:
+      {
+        auto BP = static_cast<BindPattern*>(P);
+        E.add(BP->Name->getCanonicalText(), V);
+        break;
+      }
+      default:
+        ZEN_UNREACHABLE
+    }
+  }
+
+  Value Evaluator::apply(Value Op, std::vector<Value> Args) {
+    switch (Op.getKind()) {
+      case ValueKind::SourceFunction:
+      {
+        auto Fn = Op.getDeclaration();
+        Env NewEnv;
+        for (auto [Param, Arg]: zen::zip(Fn->Params, Args)) {
+          assignPattern(Param->Pattern, Arg, NewEnv);
+        }
+        switch (Fn->Body->getKind()) {
+          case NodeKind::LetExprBody:
+            return evaluateExpression(static_cast<LetExprBody*>(Fn->Body)->Expression, NewEnv);
+          default:
+            ZEN_UNREACHABLE
+        }
+      }
+      case ValueKind::NativeFunction:
+      {
+        auto Fn = Op.getBinding();
+        return Fn(Args);
+      }
+      default:
+        ZEN_UNREACHABLE
+    }
+  }
+
+  void Evaluator::evaluate(Node* N, Env& E) {
+    switch (N->getKind()) {
+      case NodeKind::SourceFile:
+      {
+        auto SF = static_cast<SourceFile*>(N);
+        for (auto Element: SF->Elements) {
+          evaluate(Element, E);
+        }
+        break;
+      }
+      case NodeKind::ExpressionStatement:
+      {
+        auto ES = static_cast<ExpressionStatement*>(N);
+        evaluateExpression(ES->Expression, E);
+        break;
+      }
+      case NodeKind::LetDeclaration:
+      {
+        auto Decl = static_cast<LetDeclaration*>(N);
+        if (Decl->isFunction()) {
+          E.add(Decl->getNameAsString(), Decl);
+        } else {
+          Value V;
+          if (Decl->Body) {
+            switch (Decl->Body->getKind()) {
+              case NodeKind::LetExprBody:
+              {
+                auto Body = static_cast<LetExprBody*>(Decl->Body);
+                V = evaluateExpression(Body->Expression, E);
+              }
+              default:
+                ZEN_UNREACHABLE
+            }
+          }
+        }
+        break;
+      }
+      default:
+        ZEN_UNREACHABLE
+    }
+  }
+
+}