diff --git a/include/tvm/relay/base.h b/include/tvm/relay/base.h
index 4ae35f585c6f..b7621e20cf6a 100644
--- a/include/tvm/relay/base.h
+++ b/include/tvm/relay/base.h
@@ -22,8 +22,15 @@ namespace tvm {
  * You can find more about Relay by reading the language reference.
  */
 namespace relay {
+
+#define RELAY_DEBUG(...) \
+{ auto fdebug = runtime::Registry::Get("relay.debug"); \
+  CHECK(fdebug) << "Could not find Relay Python debugger function."; \
+  (*fdebug)("RELAY_DEBUG", __FILE__, __LINE__, __VA_ARGS__); \
+}
+
 /*!
- * \brief we always used NodeRef for referencing nodes.
+ * \brief We always used NodeRef for referencing nodes.
  *
  *  By default, NodeRef is a std::shared_ptr of node
  */
diff --git a/include/tvm/relay/build_module.h b/include/tvm/relay/build_module.h
new file mode 100644
index 000000000000..ed889eba0bd0
--- /dev/null
+++ b/include/tvm/relay/build_module.h
@@ -0,0 +1,76 @@
+/*!
+ *  Copyright (c) 2018 by Contributors
+ * \file tvm/relay/build_module.h
+ * \brief The passes and data structures needed to build a
+ * tvm::Module from a Relay program.
+ */
+#ifndef TVM_RELAY_BUILD_MODULE_H_
+#define TVM_RELAY_BUILD_MODULE_H_
+
+#include <tvm/lowered_func.h>
+#include <tvm/relay/environment.h>
+#include <tvm/relay/expr.h>
+#include <string>
+
+namespace tvm {
+namespace relay {
+
+/*! \brief A lowered Relay operation.
+ *
+ * A lowered operation is a pair containing the "primitive" function used
+ * to produce the lowered function as well as the lowered function itself.
+ */
+class LoweredOp;
+/*! \brief Call container. */
+class LoweredOpNode : public Node {
+ public:
+  /*!
+   * \brief The primitive function to be lowered.
+   *
+   * A primitive function consists only of calls to relay::Op which
+   * can be fused.
+   */
+  Function func;
+
+  /*!
+   * \brief The lowered function.
+   */
+  LoweredFunc lowered_func;
+
+  void VisitAttrs(tvm::AttrVisitor* v) final {
+    v->Visit("func", &func);
+    v->Visit("lowered_func", &lowered_func);
+  }
+
+  TVM_DLL static LoweredOp make(
+      Function func,
+      LoweredFunc lowered_func);
+
+  static constexpr const char* _type_key = "relay.LoweredOp";
+  TVM_DECLARE_NODE_TYPE_INFO(LoweredOpNode, Node);
+};
+
+RELAY_DEFINE_NODE_REF(LoweredOp, LoweredOpNode, NodeRef);
+
+/*!
+ * \brief Lower the operations contained in a Relay expression.
+ *
+ * The lowering pass will only lower functions marked as primitive,
+ * the FuseOps pass will provide this behavior, if run before LowerOps.
+ *
+ * \note This will do a reachability analysis and lower all definitions
+ * reachable from the provided expression.
+ *
+ * \param env  The environment.
+ * \param expr The expression with operations to be lowered.
+ * \param target The target to lower the functions to.
+ *
+ * \return The set of lowered operations.
+ */
+Array<LoweredOp> LowerOps(const Environment& env, const Expr& expr,
+                          const std::string& target = "llvm");
+
+}  // namespace relay
+}  // namespace tvm
+
+#endif  // TVM_RELAY_BUILD_MODULE_H_
diff --git a/include/tvm/relay/expr.h b/include/tvm/relay/expr.h
index 2e3bbadb7841..029470c067ce 100644
--- a/include/tvm/relay/expr.h
+++ b/include/tvm/relay/expr.h
@@ -213,12 +213,18 @@ class FunctionNode : public ExprNode {
    */
   tvm::Array<TypeVar> type_params;
 
+  /*!
+   * \brief The attributes which store metadata about functions.
+   */
+  tvm::Attrs attrs;
+
   void VisitAttrs(tvm::AttrVisitor* v) final {
     v->Visit("params", &params);
     v->Visit("body", &body);
     v->Visit("ret_type", &ret_type);
     v->Visit("type_params", &type_params);
     v->Visit("span", &span);
+    v->Visit("attrs", &attrs);
     v->Visit("_checked_type_", &checked_type_);
   }
 
@@ -233,7 +239,8 @@ class FunctionNode : public ExprNode {
   TVM_DLL static Function make(tvm::Array<Var> params,
                                Expr body,
                                Type ret_type,
-                               tvm::Array<TypeVar> ty_params);
+                               tvm::Array<TypeVar> ty_params,
+                               tvm::Attrs attrs = Attrs());
 
   static constexpr const char* _type_key = "relay.Function";
   TVM_DECLARE_NODE_TYPE_INFO(FunctionNode, ExprNode);
@@ -241,6 +248,11 @@ class FunctionNode : public ExprNode {
 
 RELAY_DEFINE_NODE_REF(Function, FunctionNode, Expr);
 
+
+TVM_DLL NodeRef FunctionGetAttr(const Function& func, const std::string& key);
+TVM_DLL Function FunctionSetAttr(const Function& func, const std::string& key, const NodeRef& data);
+
+
 /*!
  * \brief Call corresponds to operator invocation.
  *  Corresponds to the operator in computational graph terminology.
diff --git a/include/tvm/relay/interpreter.h b/include/tvm/relay/interpreter.h
new file mode 100644
index 000000000000..1c382faaef04
--- /dev/null
+++ b/include/tvm/relay/interpreter.h
@@ -0,0 +1,140 @@
+/*!
+ *  Copyright (c) 2018 by Contributors
+ * \file tvm/relay/interpreter.h
+ * \brief An interpreter for Relay.
+ *
+ * This file implements a simple reference interpreter for Relay programs.
+ * Given a Relay environment, and a Relay expression it produces a value.
+ *
+ * The interpreter's values are a naive representation of the values that
+ * can be produced by a Relay program and are exposed via tvm::Node's
+ * system to Python for introspection and debugging.
+ *
+ * The interpreter's intent is to serve as a reference semantics for the Relay IR,
+ * as well as for debugging and testing.
+ */
+#ifndef TVM_RELAY_INTERPRETER_H_
+#define TVM_RELAY_INTERPRETER_H_
+
+#include <tvm/relay/environment.h>
+#include <tvm/relay/expr.h>
+
+namespace tvm {
+namespace relay {
+
+/*!
+ * \brief A Relay value.
+ */
+class Value;
+
+/*! \brief Evaluate an expression using the interpreter producing a value.
+ *
+ * The resulting value can be passed to Python, making it easy to use
+ * for testing and debugging.
+ *
+ * The interpreter interprets the program fragments not supported by the
+ * TVM runtime, although the interpreter is naively implemented it uses
+ * TVM operators for evaluating all operators.
+ *
+ * Our intent is that this will never be the most efficient implementation of
+ * Relay's semantics, but a readable and clear one.
+ */
+Value Evaluate(Environment env, Expr e);
+
+/*! \brief The base container type of Relay values. */
+class ValueNode : public RelayNode {
+ public:
+  static constexpr const char* _type_key = "relay.Value";
+  TVM_DECLARE_BASE_NODE_INFO(ValueNode, RelayNode);
+};
+
+class Value : public NodeRef {
+ public:
+  Value() {}
+  explicit Value(NodePtr<Node> n) : NodeRef(n) {}
+  const ValueNode* operator->() const {
+    return static_cast<const ValueNode*>(node_.get());
+  }
+
+  using ContainerType = ValueNode;
+};
+
+/*! \brief A Relay closure, i.e a scope and a function. */
+class Closure;
+
+/*! \brief The container type of Closures. */
+class ClosureNode : public ValueNode {
+ public:
+  /*! \brief The set of free variables in the closure.
+   *
+   * These are the captured variables which are required for
+   * evaluation when we call the closure.
+   */
+  tvm::Map<Var, Value> env;
+  /*! \brief The function which implements the closure.
+   *
+   * \note May reference the variables contained in the env.
+   */
+  Function func;
+
+  ClosureNode() {}
+
+  void VisitAttrs(tvm::AttrVisitor* v) final {
+    v->Visit("env", &env);
+    v->Visit("func", &func);
+  }
+
+  TVM_DLL static Closure make(tvm::Map<Var, Value> env, Function func);
+
+  static constexpr const char* _type_key = "relay.Closure";
+  TVM_DECLARE_NODE_TYPE_INFO(ClosureNode, ValueNode);
+};
+
+RELAY_DEFINE_NODE_REF(Closure, ClosureNode, Value);
+
+/*! \brief A tuple value. */
+class TupleValue;
+
+/*! \brief Tuple (x, ... y). */
+struct TupleValueNode : ValueNode {
+  tvm::Array<Value> fields;
+
+  TupleValueNode() {}
+
+  void VisitAttrs(tvm::AttrVisitor* v) final { v->Visit("fields", &fields); }
+
+  TVM_DLL static TupleValue make(tvm::Array<Value> value);
+
+  static constexpr const char* _type_key = "relay.TupleValue";
+  TVM_DECLARE_NODE_TYPE_INFO(TupleValueNode, ValueNode);
+};
+
+RELAY_DEFINE_NODE_REF(TupleValue, TupleValueNode, Value);
+
+/*! \brief A tensor value. */
+class TensorValue;
+
+/*! \brief The tensor value container, wrapping an NDArray. */
+struct TensorValueNode : ValueNode {
+  runtime::NDArray data;
+
+  TensorValueNode() {}
+
+  void VisitAttrs(tvm::AttrVisitor* v) final { v->Visit("data", &data); }
+
+  /*! \brief Build a value from an NDArray. */
+  TVM_DLL static TensorValue make(runtime::NDArray data);
+
+  /*! \brief Construct an empty tensor value from t. */
+  TVM_DLL static TensorValue FromType(const Type& t);
+
+  static constexpr const char* _type_key = "relay.TensorValue";
+  TVM_DECLARE_NODE_TYPE_INFO(TensorValueNode, ValueNode);
+};
+
+RELAY_DEFINE_NODE_REF(TensorValue, TensorValueNode, Value);
+
+
+}  // namespace relay
+}  // namespace tvm
+#endif  // TVM_RELAY_INTERPRETER_H_
diff --git a/include/tvm/relay/pass.h b/include/tvm/relay/pass.h
index bf16c7ed8e33..b29678106d21 100644
--- a/include/tvm/relay/pass.h
+++ b/include/tvm/relay/pass.h
@@ -8,6 +8,7 @@
 
 #include <tvm/relay/environment.h>
 #include <tvm/relay/expr.h>
+#include <string>
 
 namespace tvm {
 namespace relay {
@@ -20,7 +21,8 @@ namespace relay {
  * populated with the result type.
  *
  * \param expr The expression to type check.
- * \param env The environment used for referencing global functions, can be None.
+ * \param env The environment used for referencing global functions, can be
+ * None.
  *
  * \return A type checked expression with its checked_type field populated.
  */
@@ -35,7 +37,8 @@ Expr InferType(const Expr& expr, const Environment& env);
  * \return A type checked Function with its checked_type field populated.
  * \note this function mutates env and is not thread-safe.
  */
-Function InferType(const Function& f, const Environment& env, const GlobalVar& var);
+Function InferType(const Function& f, const Environment& env,
+                   const GlobalVar& var);
 
 /*!
  * \brief Check that types are well kinded by applying "kinding rules".
@@ -94,28 +97,30 @@ bool AlphaEqual(const Type& t1, const Type& t2);
  *
  * For example, the expression `let x = 1 in let x = 2 in 3` bound x twice.
  *
- * `let f = (\x -> x) in let g = (\x -> x + 1) in f(g(2))` also bound x twice, although x is not shadowed.
+ * `let f = (\x -> x) in let g = (\x -> x + 1) in f(g(2))` also bound x twice,
+ * although x is not shadowed.
  *
- * \param e the expression to check.
+  * \param expr the expression to check.
  *
- * \return true iff all Var in e is bound at most once.
+  * \return true iff all Var in expr is bound at most once.
  */
-bool WellFormed(const Expr& e);
+bool WellFormed(const Expr& expr);
 
-/*! \brief Get free Vars from expr in PostDFS order.
+/*! \brief Get free type parameters from expression expr.
  *
  * Free variables are variables that are not bound by a
  * let or a function parameter in the context.
  *
  * \param expr the expression.
  *
- * \return List of free vars, in the PostDFS order visited by expr.
+ * \return List of free vars, in the PostDFS order in the expression.
  */
 tvm::Array<Var> FreeVars(const Expr& expr);
 
 /*! \brief Get free TypeVars from expression expr.
  *
- * Free type parameters are type parameters that are not bound by a function type in the context.
+ * Free type parameters are type parameters that are not bound by a function
+ * type in the context.
  *
  * \param expr the expression.
  *
@@ -125,10 +130,12 @@ tvm::Array<TypeVar> FreeTypeVars(const Expr& expr);
 
 /*! \brief Remove expressions which does not effect the program result.
  *
- * It will remove let binding that are not referenced, and if branch that are not entered.
+ * It will remove let bindings which are not referenced, and branches that will
+ * not be entered.
  *
- * For example, this pass should turn `let a = 1 in 2` into `2`, as the value of the expression does not depend on a.
- * Another example is `if (true) then 1 else 2` will be optimized into 1.
+ * For example, this pass should turn `let a = 1 in 2` into `2`, as the value of
+ * the expression does not depend on a. Another example is `if (true) then 1
+ * else 2` will be optimized into 1.
  *
  * \param e the expression to optimize.
  *
@@ -136,27 +143,30 @@ tvm::Array<TypeVar> FreeTypeVars(const Expr& expr);
  */
 Expr DeadCodeElimination(const Expr& e);
 
-/*! \brief Hash a Relay type.
- *
- * Implements structural hashing of a Relay type.
- *
- *  \param type the type to hash.
- *
- *  \return the hash value.
- */
-size_t StructuralHash(const Type& type);
-
-/*! \brief Hash a Relay expression.
- *
- * Implements structural hashing of a Relay expression.
- *
- * \param expr the expression to hash.
- *
- * \return the hash value.
- */
-size_t StructuralHash(const Expr& expr);
+/*! \brief A hashing structure in the style of std::hash. */
+struct StructuralHash {
+  /*! \brief Hash a Relay type.
+   *
+   * Implements structural hashing of a Relay type.
+   *
+   *  \param type the type to hash.
+   *
+   *  \return the hash value.
+   */
+  size_t operator()(const Type& type) const;
 
+  /*! \brief Hash a Relay expression.
+   *
+   * Implements structural hashing of a Relay expression.
+   *
+   * \param expr the expression to hash.
+   *
+   * \return the hash value.
+   */
+  size_t operator()(const Expr& expr) const;
+};
 
 }  // namespace relay
 }  // namespace tvm
+
 #endif  // TVM_RELAY_PASS_H_
diff --git a/python/tvm/relay/__init__.py b/python/tvm/relay/__init__.py
index 731a816460ee..d3b60c1174fa 100644
--- a/python/tvm/relay/__init__.py
+++ b/python/tvm/relay/__init__.py
@@ -1,5 +1,7 @@
 # pylint: disable=wildcard-import, redefined-builtin, invalid-name
 """The Relay IR namespace containing the IR definition and compiler."""
+from __future__ import absolute_import
+from ..api import register_func
 from . import base
 from . import ty
 from . import expr
@@ -15,6 +17,7 @@
 from . import vision
 from . import image
 
+
 from .scope_builder import ScopeBuilder
 
 # Span
@@ -46,6 +49,21 @@
 If = expr.If
 TupleGetItem = expr.TupleGetItem
 
+
 # helper functions
 var = expr.var
 const = expr.const
+
+@register_func("relay._tensor_value_repr")
+def _tensor_value_repr(tv):
+    return str(tv.data.asnumpy())
+
+@register_func("relay._constant_repr")
+def _tensor_constant_repr(tv):
+    return str(tv.data.asnumpy())
+
+# pylint: disable=unused-argument
+@register_func("relay.debug")
+def _debug(*args):
+    import pdb
+    pdb.set_trace()
diff --git a/python/tvm/relay/_interpreter.py b/python/tvm/relay/_interpreter.py
new file mode 100644
index 000000000000..d04319c17a99
--- /dev/null
+++ b/python/tvm/relay/_interpreter.py
@@ -0,0 +1,4 @@
+"""The interface to the Evaluator exposed from C++."""
+from tvm._ffi.function import _init_api
+
+_init_api("relay._interpreter", __name__)
diff --git a/python/tvm/relay/env.py b/python/tvm/relay/env.py
index 9c3241e18ef8..37e0999dce9e 100644
--- a/python/tvm/relay/env.py
+++ b/python/tvm/relay/env.py
@@ -45,9 +45,12 @@ def __setitem__(self, var, func):
         func: Function
             The function.
         """
+        return self._add(var, func)
+
+    def _add(self, var, func, update=False):
         if isinstance(var, _base.string_types):
             var = _expr.GlobalVar(var)
-        _env.Environment_Add(self, var, func)
+        return _env.Environment_Add(self, var, func, update)
 
     def __getitem__(self, var):
         """Lookup a global function by name or by variable.
diff --git a/python/tvm/relay/graph_runtime_codegen.py b/python/tvm/relay/graph_runtime_codegen.py
new file mode 100644
index 000000000000..d0ce239fa7fd
--- /dev/null
+++ b/python/tvm/relay/graph_runtime_codegen.py
@@ -0,0 +1,551 @@
+"""
+A compiler from a Relay expression to TVM's graph runtime.
+
+The compiler is built from a few pieces.
+
+First we define a compiler from a single Relay expression to the
+graph langauge. We require the expression to be a function.
+The function's parameters correpond to the placeholder/inputs
+and model parameters found in the computation graph representation.
+The body of the function represents the computation graph.
+
+The compiler's output is a program in the graph language, which is composed of
+graph langauge is composed of Node, NodeRef, InputNode, OpNode.
+This "little language" represents programs in TVM's graph format.
+
+To connect to the graph runtime, we use a printer that converts our graph format
+into TVM's JSON format. The resulting string can be loaded by
+contrib.graph_runtime or any other TVM runtime comptatible system.
+
+We expose this functionality in compile_to_tvm.
+"""
+
+from __future__ import absolute_import
+import json
+import attr
+from . import ir_pass
+from .op import Op
+from .expr import Var, Function, Call, If, GlobalVar, Constant, Let, Tuple
+from ..build_module import build as tvm_build_module
+from .. contrib import graph_runtime
+from .ir_pass import infer_type
+from .. import cpu
+
+class AbstractExprVisitor(object):
+    """A visitor over Expr in Python."""
+
+    def __init__(self):
+        self.memo_map = {}
+
+    # pylint: disable=no-else-return
+    def visit(self, expr):
+        """Apply the visitor to an expression."""
+        found = self.memo_map.get(expr)
+        if found:
+            return found
+
+        if isinstance(expr, Function):
+            res = self.visit_function(expr)
+        elif isinstance(expr, Call):
+            res = self.visit_call(expr)
+        elif isinstance(expr, Let):
+            res = self.visit_let(expr)
+        elif isinstance(expr, Var):
+            res = self.visit_var(expr)
+        elif isinstance(expr, GlobalVar):
+            res = self.visit_global_var(expr)
+        elif isinstance(expr, If):
+            res = self.visit_if(expr)
+        elif isinstance(expr, Tuple):
+            res = self.visit_tuple(expr)
+        elif isinstance(expr, Constant):
+            res = self.visit_constant(expr)
+        else:
+            raise Exception("warning unhandled case: {0}".format(type(expr)))
+
+        self.memo_map[expr] = res
+        return res
+
+    def visit_function(self, _):
+        raise Exception("Abstract method please implement me.")
+
+    def visit_let(self, _):
+        raise Exception("Abstract method please implement me.")
+
+    def visit_call(self, _):
+        raise Exception("Abstract method please implement me.")
+
+    def visit_var(self, _):
+        raise Exception("Abstract method please implement me.")
+
+    def visit_type(self, typ):
+        return typ
+
+    def visit_if(self, _):
+        raise Exception("Abstract method please implement me.")
+
+    def visit_tuple(self, _):
+        raise Exception("Abstract method please implement me.")
+
+    def visit_constant(self, _):
+        raise Exception("Abstract method please implement me.")
+
+    def visit_global_var(self, _):
+        raise Exception("Abstract method please implement me.")
+
+
+class ExprMutator(AbstractExprVisitor):
+    """A functional visitor over Expr in Python."""
+
+    def visit_function(self, fn):
+        new_body = self.visit(fn.body)
+        return Function(
+            list(fn.params),
+            fn.ret_type, new_body,
+            fn.type_params)
+
+    def visit_let(self, let):
+        new_var = self.visit(let.var)
+        new_val = self.visit(let.value)
+        new_body = self.visit(let.body)
+        return Let(new_var, new_val, new_body)
+
+    def visit_call(self, call):
+        new_fn = self.visit(call.op)
+        new_args = [self.visit(arg) for arg in call.args]
+        return Call(new_fn, new_args, call.attrs)
+
+    def visit_var(self, var):
+        return var
+
+    def visit_global_id(self, global_var):
+        return global_var
+
+    def visit_if(self, ite):
+        return If(
+            self.visit(ite.guard),
+            self.visit(ite.true_b),
+            self.visit(ite.false_b))
+
+    def visit_tuple(self, tup):
+        return Tuple([self.visit(field) for field in tup.fields])
+
+    def visit_constant(self, const):
+        return const
+
+
+@attr.s
+class NodeRef(object):
+    """A reference to a node, used for constructing the graph."""
+    ident = attr.ib()
+    index = attr.ib(default=0)
+    version = attr.ib(default=0)
+
+    def to_json(self):
+        return [self.ident, self.index, self.version]
+
+
+@attr.s
+class Node(object):
+    """The base class for nodes in the TVM runtime system graph input."""
+    name = attr.ib()
+    attrs = attr.ib()
+    is_output = attr.ib()
+
+    def to_json(self):
+        raise Exception("Abstract method, please implement me.")
+
+
+@attr.s
+class InputNode(Node):
+    """An input node in the TVM runtime system graph input."""
+    name = attr.ib()
+    attrs = attr.ib()
+    is_output = attr.ib(default=False)
+
+    def to_json(self):
+        return {
+            "op": "null",
+            "name": self.name,
+            "inputs": []
+        }
+
+
+@attr.s
+class OpNode(Node):
+    """An operator node in the TVM runtime system's graph input."""
+    op_name = attr.ib()
+    inputs = attr.ib()
+    op_attrs = attr.ib()
+    is_output = attr.ib(default=False)
+
+    def to_json(self):
+        attrs = dict.copy(self.op_attrs)
+        # Extend ops with extra info.
+        attrs['func_name'] = self.op_name
+        # When do we flatten?
+        attrs['flatten_data'] = "0"
+        # Fix me!
+        attrs['num_inputs'] = str(len(self.inputs))
+        attrs['num_outputs'] = "1"
+
+        return {
+            "op": "tvm_op",
+            "name": self.name,
+            "attrs": attrs,
+            "inputs": self.inputs
+        }
+
+
+def shape_to_json(shape):
+    return [sh.value for sh in shape]
+
+
+def from_tensor(typ):
+    return (typ.dtype, shape_to_json(typ.shape))
+
+
+class GraphRuntimeCodegen(ExprMutator):
+    """The compiler from Relay to the TVM runtime system."""
+    nodes = attr.ib()
+    id_map = attr.ib()
+
+    def __init__(self, env):
+        ExprMutator.__init__(self)
+        self.nodes = []
+        self.id_map = {}
+        self.env = env
+
+    def add_node(self, node):
+        """
+        Add a node to the graph.
+
+        Parameters
+        ----------
+        node: Node
+            The node to add to the graph.
+
+        Returns
+        -------
+        node_ref: NodeRef
+            A reference to the node.
+
+        """
+        self.nodes.append(node)
+        ident = len(self.nodes) - 1
+        return NodeRef(ident)
+
+    def add_binding(self, ident, ref):
+        """
+        Add a identifier to node mapping.
+
+        Parameters
+        ----------
+        ident: relay.Var
+            The variable to map
+
+        ref: NodeRef
+            The node the identifier points.
+        """
+        self.id_map[ident] = ref
+
+    def let_bind(self, ident, node):
+        """
+        Let bind node to ident.
+
+        Parameters
+        ----------
+        ident: relay.Var
+            The variable to map.
+
+        ref: NodeRef
+            The node the identifier points.
+
+        Returns
+        -------
+        ref: NodeRef
+            Return reference to the node.
+        """
+        ref = self.add_node(node)
+        self.add_binding(ident, ref)
+        return ref
+
+    def get_node(self, ref):
+        """
+        Lookup a node by a node reference.
+
+        Parameters
+        ----------
+        ref: NodeRef
+            The reference to lookup.
+
+        Returns
+        -------
+        node: Node
+            The node.
+        """
+        return self.nodes[ref.ident]
+
+    def lookup(self, ident):
+        """
+        Lookup a node by identifier.
+
+        Parameters
+        ----------
+        ident: relay.Var
+            The reference to lookup.
+
+        Returns
+        -------
+        node: Node
+            The node.
+        """
+        return self.id_map[ident]
+
+    def codegen(self, func):
+        """Compile a single function into a graph.
+
+        Parameters
+        ----------
+        func: tvm.relay.Expr
+            The function to compile.
+        """
+        # First we convert all the parameters into input nodes.
+        params = func.params
+
+        for param in params:
+            dtype, shape = from_tensor(param.type_annotation)
+            node = InputNode("{0}".format(param.name_hint), {
+                "shape": shape,
+                "dtype": dtype,
+            })
+            self.let_bind(param, node)
+
+        # Then we compile the body into a graph which can depend
+        # on input variables.
+        output_ref = self.visit(func.body)
+
+        # Finally we retreive return value of program, which will
+        # become our output node.
+        self.get_node(output_ref).is_output = True
+
+    def visit_let(self, let):
+        """
+        Visit the let binding, by first traversing its value,
+        then setting the metadata on the returned NodeRef.
+
+        Finally visit the body, and return the NodeRef corresponding
+        to it.
+
+        Parameters
+        ----------
+        let: tvm.relay.Expr
+            The let binding to transform.
+
+        Returns
+        -------
+        ref: NodeRef
+            The node reference to the body.
+        """
+        ident = let.var
+        val = let.value
+        body = let.body
+
+        val_ref = self.visit(val)
+        dtype, shape = from_tensor(val.checked_type())
+        val_node = self.get_node(val_ref)
+        val_node.attrs["dtype"] = dtype
+        val_node.attrs["shape"] = shape
+        self.add_binding(ident, val_ref)
+        return self.visit(body)
+
+    def visit_var(self, var):
+        return self.lookup(var)
+
+    def visit_call(self, call):
+        """Transform a ::tvm.relay.Call into an operator in the TVM graph."""
+        inputs = []
+        for arg in call.args:
+            inputs.append(self.visit(arg).to_json())
+
+        if isinstance(call.op, Op):
+            raise Exception(
+                "Operators should be transformed away; try applying" +
+                "the fuse_ops transformation to the expression.")
+        elif isinstance(call.op, GlobalVar):
+            func = self.env[call.op]
+        elif isinstance(call.op, Function):
+            func = call.op
+        else:
+            raise Exception(
+                "TVM runtime does not support calls to {0}".format(type(call.op)))
+
+        if int(func.attrs.Primitive) != 1:
+            raise Exception(
+                "TVM only support calls to primitive functions " +
+                "(i.e functions composed of fusable operator invocations)")
+
+        op_name = func.attrs.LoweredFunc.name
+
+        attrs = {'shape': shape_to_json(call.checked_type.shape),
+                 'dtype': call.checked_type.dtype}
+        call_hash = str(ir_pass.structural_hash(call))
+        op_node = OpNode("call_" + call_hash, attrs, op_name, inputs, {})
+        return self.add_node(op_node)
+
+    def to_json(self):
+        """
+        Convert the sequence of nodes stored by the compiler into the
+        TVM graph runtime format.
+
+        Returns
+        -------
+        graph_json : str
+            The generated JSON as a string.
+        """
+        nodes = []
+        # First we compute "nodes" field.
+        for node in self.nodes:
+            nodes.append(node.to_json())
+
+        arg_nodes = []
+        heads = []
+        # Compute "arg_nodes" and "heads" fields.
+        for i, node in enumerate(self.nodes):
+            if isinstance(node, InputNode):
+                arg_nodes.append(i)
+
+            if node.is_output:
+                # Need to fix this.
+                heads.append(NodeRef(i).to_json())
+
+        def compute_node_row_ptr(nodes):
+            """Calculate the node_row_ptr field by doing a DFS backwards
+               from the output and reversing the path.
+            """
+            row_ptr = [len(nodes)]
+            discovered = set()
+            stack = []
+            stack.append(len(nodes) - 1)
+            while stack:
+                i = stack.pop()
+                if i not in discovered:
+                    discovered.add(i)
+                    row_ptr.append(i)
+                    node = nodes[i]
+                    if isinstance(node, OpNode):
+                        for inp in node.inputs:
+                            stack.append(inp[0])
+            row_ptr.reverse()
+            return row_ptr
+
+        # Compute "node_row_ptr".
+        node_row_ptr = compute_node_row_ptr(self.nodes)
+
+        # Compute "attrs" field.
+        attrs = {}
+
+        # These fields are mandatory.
+        shapes = []
+        storage_ids = []
+        dtype = []
+        dltype = []
+
+        for i, node in enumerate(self.nodes):
+            storage_ids.append(i)
+            shapes.append(node.attrs['shape'])
+            if node.attrs['dtype'] == 'float32':
+                dtype.append(0)
+                dltype.append('float32')
+
+        attrs["shape"] = ["list_shape", shapes]
+        attrs["storage_id"] = ["list_int", storage_ids]
+        attrs["dtype"] = ["list_int", dtype]
+        attrs["dltype"] = ["list_str", dltype]
+
+        json_dict = {
+            "nodes": nodes,
+            "arg_nodes": arg_nodes,
+            "heads": heads,
+            "attrs": attrs,
+            "node_row_ptr":  node_row_ptr
+        }
+
+        return json.dumps(json_dict)
+
+
+def build(env, func, target=None):
+    """
+    Compile a single function to the components needed by the
+    TVM RTS.
+
+    Parameters
+    ----------
+    func: relay.Expr
+        The function to build.
+
+    target: optional str
+        The target platform.
+
+    Returns
+    -------
+    (graph_json, mod, params): tuple of (str, tvm.Module, dict)
+        The outputs of building a Relay function for the TVM runtime.
+
+    """
+    if target is None:
+        target = 'llvm'
+
+    comp = GraphRuntimeCodegen(env)
+    # NB(@jroesch) This creates lowered functions, and generates names for them
+    #
+    # We need these names to emit the correct graph as these are names of the
+    # functions contained in the module.
+    lowered_ops = ir_pass.lower_ops(env, func)
+    mod = tvm_build_module([lf.lowered_func for lf in lowered_ops], target)
+
+    # Therefore the call to compile must come after.
+    comp.codegen(func)
+    graph_json = comp.to_json()
+    return graph_json, mod, None  # params currently isn't supported by API
+
+
+def graph_evaluate(env, func, *args):
+    """
+    Corresponding function to tvm.relay.eval.evaluate.
+
+    This function evaluates a Relay expression on the
+    TVM graph_runtime.
+
+    Parameters
+    ----------
+    env: tvm.relay.Environment
+        The global environment used.
+
+    expr: tvm.relay.Expr
+        The expression to evaluate.
+
+    args: list of tvm.relay.Expr
+        The arguments to apply to the expression, only works
+        if the expression has a function type.
+
+    Returns
+    -------
+    value: tvm.NDArray
+        The output Tensor produced by evaluating the expression.
+    """
+    func = infer_type(func, env)
+    func = ir_pass.fuse_ops(env, func)
+    func = infer_type(func, env)
+    graph_json, mod, params = build(env, func)
+    assert params is None
+    gmodule = graph_runtime.create(graph_json, mod, cpu(0))
+    # Create map of inputs.
+    inputs = {}
+    for i, arg in enumerate(args):
+        inputs[func.params[i].name_hint] = arg
+    # Set the inputs here.
+    gmodule.set_input(**inputs)
+    # Run the module, and fetch the output.
+    gmodule.run()
+    return gmodule.get_output(0)
diff --git a/python/tvm/relay/interpreter.py b/python/tvm/relay/interpreter.py
new file mode 100644
index 000000000000..06dc3c79fba4
--- /dev/null
+++ b/python/tvm/relay/interpreter.py
@@ -0,0 +1,130 @@
+#pylint: disable=no-else-return
+"""An interface to the Realy interpreter."""
+from __future__ import absolute_import
+import numpy as np
+from .. import register_func, nd
+from .base import NodeBase, register_relay_node
+from . import _make
+from . import _interpreter
+from . import ir_pass
+from .expr import Call, Constant, GlobalVar
+from . import const
+from .._ffi.base import integer_types
+
+class Value(NodeBase):
+    """Base class of all values.
+    """
+
+    @staticmethod
+    @register_func("relay.from_scalar")
+    def from_scalar(i, dtype=None):
+        """Convert a Python scalar to a Relay scalar."""
+        if dtype is None:
+            if isinstance(i, integer_types):
+                dtype = 'int32'
+            elif isinstance(i, float):
+                dtype = 'float32'
+            elif isinstance(i, bool):
+                dtype = 'uint8'
+            else:
+                raise Exception("unable to infer dtype {0}".format(type(i)))
+
+        return TensorValue(nd.array(np.array(i, dtype=dtype)))
+
+
+@register_relay_node
+class TupleValue(Value):
+    def __init__(self, *fields):
+        self.__init_handle_by_constructor__(
+            _make.TupleValue, fields)
+
+    def __getitem__(self, field_no):
+        return self.fields[field_no]
+
+
+@register_relay_node
+class Closure(Value):
+    pass
+
+
+@register_relay_node
+class TensorValue(Value):
+    """A Tensor value produced by the evaluator."""
+
+    def __init__(self, data):
+        """Allocate a new TensorValue and copy the data from `array` into
+           the new array.
+        """
+        if isinstance(data, np.ndarray):
+            data = nd.array(data)
+
+        self.__init_handle_by_constructor__(
+            _make.TensorValue, data)
+
+    def as_ndarray(self):
+        """Convert a Relay TensorValue into a tvm.ndarray."""
+        return self.data
+
+    def asnumpy(self):
+        """Convert a Relay TensorValue into a numpy.ndarray."""
+        return self.data.asnumpy()
+
+    def __eq__(self, other):
+        return self.data == other.data
+
+
+def _arg_to_ast(arg):
+    if isinstance(arg, TensorValue):
+        return Constant(arg.data)
+    elif isinstance(arg, np.ndarray):
+        return Constant(nd.array(arg))
+    elif isinstance(arg, Constant):
+        return arg
+    else:
+        return const(arg)
+
+
+def apply_passes(expr, env=None):
+    ck_expr = ir_pass.infer_type(expr, env=env)
+    fused_expr = ir_pass.fuse_ops(env, ck_expr)
+    return fused_expr
+
+
+def evaluate(env, expr, *args):
+    """
+    Evaluate a Relay expression on the interpreter.
+
+    Parameters
+    ----------
+    env: tvm.relay.Environment
+        The global environment used.
+
+    expr: tvm.relay.Expr
+        The expression to evaluate.
+
+    args: list of tvm.relay.Expr
+        The arguments to apply to the expression, only works
+        if the expression has a function type.
+
+    Returns
+    -------
+    value: tvm.relay.eval.Value
+        The value produced by evaluating the expression.
+    """
+    # assert len(args) == 0
+    relay_args = []
+    for arg in args:
+        relay_args.append(_arg_to_ast(arg))
+
+    # TODO: We need to move this optimization code into the optimizer/pass manager
+    if isinstance(expr, GlobalVar):
+        func = env[expr]
+        func = apply_passes(func, env)
+        env._add(expr, func, True)
+        opt_expr = Call(expr, relay_args)
+        # import pdb; pdb.set_trace()
+        return _interpreter.evaluate(env, opt_expr)
+    else:
+        expr = Call(expr, relay_args)
+        opt_expr = apply_passes(expr, env)
+        return _interpreter.evaluate(env, opt_expr)
diff --git a/python/tvm/relay/ir_pass.py b/python/tvm/relay/ir_pass.py
index 6adfaacdc86d..1940c8d60d7f 100644
--- a/python/tvm/relay/ir_pass.py
+++ b/python/tvm/relay/ir_pass.py
@@ -211,3 +211,9 @@ def structural_hash(value):
         msg = ("found value of type {0} expected" +
                "relay.Expr or relay.Type").format(type(value))
         raise TypeError(msg)
+
+def fuse_ops(expr, env):
+    return _ir_pass.FuseOps(env, expr)
+
+def lower_ops(env, expr, target='llvm'):
+    return _ir_pass.LowerOps(env, expr, target)
diff --git a/python/tvm/relay/op/_tensor.py b/python/tvm/relay/op/_tensor.py
index 0bc2054cebdf..6ccb394ef8db 100644
--- a/python/tvm/relay/op/_tensor.py
+++ b/python/tvm/relay/op/_tensor.py
@@ -1,2 +1,49 @@
-#pylint: disable=invalid-name
+#pylint: disable=invalid-name, unused-argument
 """Backend compiler related feature registration"""
+import tvm
+import topi
+from . import register
+
+def add_compute(attrs, inputs, output_type, target):
+    assert len(inputs) == 2
+    return [topi.add(inputs[0], inputs[1])]
+
+def add_schedule(outputs, target):
+    assert len(outputs) == 1
+    return tvm.create_schedule(outputs[0].op)
+
+register("add", "FTVMCompute", add_compute)
+register("add", "FTVMSchedule", add_schedule)
+
+def subtract_compute(attrs, inputs, output_type, target):
+    assert len(inputs) == 2
+    return [topi.subtract(inputs[0], inputs[1])]
+
+def subtract_schedule(outputs, target):
+    assert len(outputs) == 1
+    return tvm.create_schedule(outputs[0].op)
+
+register("subtract", "FTVMCompute", subtract_compute)
+register("subtract", "FTVMSchedule", subtract_schedule)
+
+def multiply_compute(attrs, inputs, output_type, target):
+    assert len(inputs) == 2
+    return [topi.multiply(inputs[0], inputs[1])]
+
+def multiply_schedule(outputs, target):
+    assert len(outputs) == 1
+    return tvm.create_schedule(outputs[0].op)
+
+register("multiply", "FTVMCompute", multiply_compute)
+register("multiply", "FTVMSchedule", multiply_schedule)
+
+def equal_compute(attrs, inputs, output_type, target):
+    assert len(inputs) == 2
+    return [topi.equal(inputs[0], inputs[1])]
+
+def equal_schedule(outputs, target):
+    assert len(outputs) == 1
+    return tvm.create_schedule(outputs[0].op)
+
+register("equal", "FTVMCompute", equal_compute)
+register("equal", "FTVMSchedule", equal_schedule)
diff --git a/python/tvm/relay/op/nn/_nn.py b/python/tvm/relay/op/nn/_nn.py
new file mode 100644
index 000000000000..4f5dcd4dd08b
--- /dev/null
+++ b/python/tvm/relay/op/nn/_nn.py
@@ -0,0 +1,16 @@
+#pylint: disable=invalid-name, unused-argument
+"""Backend compiler related feature registration"""
+import tvm
+import topi
+from .. import register
+
+def dense_compiler(attrs, inputs, output_type):
+    assert len(inputs) == 2
+    return [topi.nn.dense(inputs[0], inputs[1])]
+
+def dense_schedule(outputs, target):
+    assert len(outputs) == 1
+    return tvm.create_schedule(outputs[0].op)
+
+register("nn.dense", "FTVMCompute", dense_compiler)
+register("nn.dense", "FTVMSchedule", dense_schedule)
diff --git a/python/tvm/relay/op/op.py b/python/tvm/relay/op/op.py
index f1130b52e7ce..0c09f39a3c83 100644
--- a/python/tvm/relay/op/op.py
+++ b/python/tvm/relay/op/op.py
@@ -3,7 +3,8 @@
 
 from ..base import register_relay_node
 from ..expr import Expr
-
+from ...api import register_func
+from ...build_module import lower, build
 
 @register_relay_node
 class Op(Expr):
@@ -75,3 +76,11 @@ def _register(v):
 
 
 _init_api("relay.op", __name__)
+
+@register_func("relay.op.compiler._lower")
+def _lower(name, schedule, inputs, outputs):
+    return lower(schedule, list(inputs) + list(outputs), name=name)
+
+@register_func("relay.op.compiler._build")
+def _build(lowered_funcs):
+    return build(lowered_funcs, target="llvm")
diff --git a/python/tvm/relay/testing/mlp.py b/python/tvm/relay/testing/mlp.py
index 67fa0d90c643..7d7d984f7526 100644
--- a/python/tvm/relay/testing/mlp.py
+++ b/python/tvm/relay/testing/mlp.py
@@ -17,6 +17,7 @@
 """
 a simple multilayer perceptron
 """
+from __future__ import absolute_import
 from tvm import relay
 from .init import create_workload
 
diff --git a/src/relay/interpreter.cc b/src/relay/interpreter.cc
new file mode 100644
index 000000000000..534a2a980e4a
--- /dev/null
+++ b/src/relay/interpreter.cc
@@ -0,0 +1,432 @@
+/*!
+ *  Copyright (c) 2018 by Contributors
+ * \file src/tvm/relay/interpreter.cc
+ * \brief An interpreter for the Relay IR.
+ */
+
+#include <tvm/codegen.h>
+#include <tvm/packed_func_ext.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/interpreter.h>
+#include <tvm/relay/logging.h>
+#include <tvm/relay/pass.h>
+#include <tvm/relay/build_module.h>
+#include "./ir/type_functor.h"
+
+namespace tvm {
+namespace relay {
+
+using namespace runtime;
+
+inline const PackedFunc& GetPackedFunc(const std::string& name) {
+  const PackedFunc* pf = tvm::runtime::Registry::Get(name);
+  CHECK(pf != nullptr) << "Cannot find function " << name << " in registry";
+  return *pf;
+}
+
+/* Value Implementation */
+Closure ClosureNode::make(tvm::Map<Var, Value> env, Function func) {
+  NodePtr<ClosureNode> n = make_node<ClosureNode>();
+  n->env = std::move(env);
+  n->func = std::move(func);
+  return Closure(n);
+}
+
+TVM_REGISTER_API("relay._make.Closure")
+    .set_body([](TVMArgs args, TVMRetValue* ret) {
+      *ret = ClosureNode::make(args[0], args[1]);
+    });
+
+TVM_STATIC_IR_FUNCTOR_REGISTER(IRPrinter, vtable)
+    .set_dispatch<ClosureNode>([](const ClosureNode* node, tvm::IRPrinter* p) {
+      p->stream << "ClosureNode(" << node->func << ")";
+    });
+
+TupleValue TupleValueNode::make(tvm::Array<Value> value) {
+  NodePtr<TupleValueNode> n = make_node<TupleValueNode>();
+  n->fields = value;
+  return TupleValue(n);
+}
+
+TVM_REGISTER_API("relay._make.TupleValue")
+    .set_body([](TVMArgs args, TVMRetValue* ret) {
+      *ret = TupleValueNode::make(args[0]);
+    });
+
+TVM_STATIC_IR_FUNCTOR_REGISTER(IRPrinter, vtable)
+    .set_dispatch<TupleValueNode>([](const TupleValueNode* node,
+                                     tvm::IRPrinter* p) {
+      p->stream << "TupleValueNode(" << node->fields << ")";
+    });
+
+TensorValue TensorValueNode::make(runtime::NDArray data) {
+  NodePtr<TensorValueNode> n = make_node<TensorValueNode>();
+  n->data = std::move(data);
+  return TensorValue(n);
+}
+
+TVM_STATIC_IR_FUNCTOR_REGISTER(IRPrinter, vtable)
+    .set_dispatch<TensorValueNode>([](const TensorValueNode* node,
+                                      tvm::IRPrinter* p) {
+      auto to_str = GetPackedFunc("relay._tensor_value_repr");
+      std::string data_str = to_str(GetRef<TensorValue>(node));
+      p->stream << "TensorValueNode(" << data_str << ")";
+    });
+
+TensorValue TensorValueNode::FromType(const Type& t) {
+  if (auto tt_node = t.as<TensorTypeNode>()) {
+    std::vector<int64_t> dims;
+
+    for (auto dim : tt_node->shape) {
+      auto int_node = dim.as<tvm::ir::IntImm>();
+      CHECK(int_node) << "expected concrete dimensions";
+      dims.push_back(int_node->value);
+    }
+
+    DLDataType dtype;
+    DLContext context;
+
+    switch (tt_node->dtype.code()) {
+      case halideir_type_int:
+        dtype.code = kDLInt;
+        break;
+      case halideir_type_uint:
+        dtype.code = kDLUInt;
+        break;
+      case halideir_type_float:
+        dtype.code = kDLFloat;
+        break;
+      default:
+        throw dmlc::Error("can not convert HalideIR type into DLTensor dtype");
+    }
+
+    dtype.bits = tt_node->dtype.bits();
+    dtype.lanes = tt_node->dtype.lanes();
+
+    // TODO(@jroesch): Is this the right place to place the tensor?
+    context.device_type = DLDeviceType::kDLCPU;
+    context.device_id = 0;
+    runtime::NDArray data = NDArray::Empty(dims, dtype, context);
+    return TensorValueNode::make(data);
+  } else {
+    LOG(FATAL) << "expected a tensor type";
+    return TensorValue();
+  }
+}
+
+TVM_REGISTER_API("relay._make.TensorValue")
+    .set_body([](TVMArgs args, TVMRetValue* ret) {
+      runtime::NDArray data = args[0];
+      *ret = TensorValueNode::make(data);
+    });
+
+/* Evaluator Implementation. */
+struct EvalError : dmlc::Error {
+  explicit EvalError(const std::string& msg) : Error(msg) {}
+};
+
+/*!
+ * \brief A stack frame in the Relay interpreter.
+ *
+ * Contains a mapping from relay::Var to relay::Value.
+ */
+struct Frame {
+  /*! \brief The set of local variables and arguments for the frame. */
+  tvm::Map<Var, Value> locals;
+
+  explicit Frame(tvm::Map<Var, Value> locals) : locals(locals) {}
+};
+
+/*!
+ * \brief The call stack in the Relay interpreter.
+ *
+ * Contains a stack of frames; each corresponding to
+ * a function call.
+ */
+struct Stack {
+  /*! \brief The stack frames. */
+  std::vector<Frame> frames;
+  Stack() : frames() { frames.push_back(Frame({})); }
+
+  Frame& current_frame() { return frames.back(); }
+
+  Value Lookup(const Var& local) {
+    for (auto frame = frames.rbegin(); frame != frames.rend(); frame++) {
+      auto elem = frame->locals.find(local);
+      if (elem != frame->locals.end()) {
+        return (*elem).second;
+      }
+    }
+
+    LOG(FATAL) << "could not find variable binding for " << local
+               << "address= " << local.operator->();
+    return Value();
+  }
+  /*!
+   * A wrapper around Frame to add RAII semantics to pushing and popping
+   * stack frames.
+   */
+  struct LocalFrame {
+    Stack& st;
+    explicit LocalFrame(Stack& st, const Frame& fr) : st(st) {
+      st.frames.push_back(fr);
+    }
+    ~LocalFrame() { st.frames.pop_back(); }
+  };
+};
+
+/*! \brief The equal comparator for expressions. */
+struct ExprEqual {
+  bool operator()(const Expr& a, const Expr& b) const {
+    return AlphaEqual(a, b);
+  }
+};
+
+struct Interpreter : ExprFunctor<Value(const Expr& n)> {
+  Environment env;
+  Stack stack;
+  using JitKey = Function;
+
+  using OpMap = std::unordered_map<JitKey, PackedFunc, StructuralHash, ExprEqual>;
+
+  OpMap operator_map_;
+
+  template <typename T>
+  T with_frame(const Frame& fr, const std::function<T()>& f) {
+    Stack::LocalFrame lf(stack, fr);
+    return f();
+  }
+
+  Interpreter(Environment env) : env(env), operator_map_() {}
+  Interpreter(Environment env, OpMap operator_map) : env(env), operator_map_(operator_map) {}
+
+  void extend(const Var& id, Value v) {
+    this->stack.current_frame().locals.Set(id, v);
+  }
+
+  inline Value Lookup(const Var& local) {
+    return this->stack.Lookup(local);
+  }
+
+  Value Eval(const Expr& expr) {
+    return (*this)(expr);
+  }
+
+  Value VisitExpr(const Expr& expr) override {
+    RELAY_LOG(INFO) << "VisitExpr: " << expr << std::endl;
+    auto ret = ExprFunctor<Value(const Expr& n)>::VisitExpr(expr);
+    return ret;
+  }
+
+  Value VisitExpr_(const VarNode* var_node) override {
+    return Lookup(GetRef<Var>(var_node));
+  }
+
+  Value VisitExpr_(const GlobalVarNode* op) override {
+    return Eval(this->env->Lookup(GetRef<GlobalVar>(op)));
+  }
+
+  Value VisitExpr_(const OpNode* id) override {
+    // TODO(@jroesch): Eta-expand and return in this case.
+    throw EvalError(
+        "internal error, need to wrap intrinsic into call synthetic call node "
+        "in "
+        "this case, eta expand");
+  }
+
+  Value VisitExpr_(const ConstantNode* op) override {
+    return TensorValueNode::make(op->data);
+  }
+
+  Value VisitExpr_(const TupleNode* op) override {
+    std::vector<Value> values;
+
+    for (const auto& field : op->fields) {
+      Value field_value = Eval(field);
+      values.push_back(field_value);
+    }
+
+    return TupleValueNode::make(values);
+  }
+
+  Value VisitExpr_(const FunctionNode* func_node) override {
+    auto func = GetRef<Function>(func_node);
+    tvm::Map<Var, Value> captured_env;
+    Array<Var> free_vars = FreeVars(func);
+
+    for (const auto& var : free_vars) {
+      captured_env.Set(var, Eval(var));
+    }
+
+    return ClosureNode::make(captured_env, func);
+  }
+
+  inline Value InvokeCompiledOp(PackedFunc func, const Array<Value>& args,
+                                Type ret_type) {
+    // Marshal the arguments.
+    auto arg_len = args.size() + 1;
+    std::vector<TVMValue> values(arg_len);
+    std::vector<int> codes(arg_len);
+    TVMArgsSetter setter(values.data(), codes.data());
+    TVMRetValue ret;
+
+    // We need real type information to properly allocate the structure.
+    for (size_t i = 0; i < args.size(); i++) {
+      if (const TensorValueNode* tv = args[i].as<TensorValueNode>()) {
+        setter(i, tv->data);
+      }
+    }
+
+    // TVM's calling convention is that the final argument is the output
+    // buffer. To preserve the illusion of being a functional language
+    // we need to allocate space for the output buffer based on the
+    // return type.
+    CHECK(ret_type.as<TensorTypeNode>());
+
+    auto out_tensor = TensorValueNode::FromType(ret_type);
+
+    setter(arg_len - 1, out_tensor->data);
+    func.CallPacked(TVMArgs(values.data(), codes.data(), arg_len), &ret);
+    return out_tensor;
+  }
+
+  Value Invoke(const Closure& closure, const tvm::Array<Value>& args) {
+    // Get a reference to the function inside the closure.
+    auto func = closure->func;
+    auto compiled = operator_map_.find(func);
+    tvm::Array<Function> funcs;
+    for (auto op : operator_map_) {
+      funcs.push_back(op.first);
+    }
+
+    // This case we know we have precompiled the operator.
+    if (compiled != operator_map_.end()) {
+      auto func_ty = func->func_type_annotation();
+      return InvokeCompiledOp(compiled->second, args, func_ty->ret_type);
+    }
+
+    // Allocate a frame with the parameters and free variables.
+    tvm::Map<Var, Value> locals;
+
+    CHECK_EQ(func->params.size(), args.size());
+
+    for (size_t i = 0; i < func->params.size(); i++) {
+      CHECK_EQ(locals.count(func->params[i]), 0);
+      locals.Set(func->params[i], args[i]);
+    }
+
+    // Add the var to value mappings from the Closure's environment.
+    for (auto it = closure->env.begin(); it != closure->env.end(); ++it) {
+      CHECK_EQ(locals.count((*it).first), 0);
+      locals.Set((*it).first, (*it).second);
+    }
+
+    return with_frame<Value>(Frame(locals), [&]() { return Eval(func->body); });
+  }
+
+  Value VisitExpr_(const CallNode* call) override {
+    tvm::Array<Value> args;
+    for (auto arg : call->args) {
+      args.push_back(Eval(arg));
+    }
+
+    // We should not find operators after running fusion,
+    // and operator lowering.
+    //
+    // We have some functions cotaining chunks of operators
+    // which will be loaded into operator map.
+    if (auto op_node = call->op.as<OpNode>()) {
+      LOG(FATAL) << "found " << op_node->name
+                 << "; operators should be removed by future passes; try "
+                    "fusing and lowering";
+    }
+
+    // Now we just evaluate and expect to find a closure.
+    Value fn_val = Eval(call->op);
+    if (const ClosureNode* closure_node = fn_val.as<ClosureNode>()) {
+      auto closure = GetRef<Closure>(closure_node);
+      return this->Invoke(closure, args);
+    } else {
+      throw EvalError(
+          "internal error: type error, expected function value in the call "
+          "position");
+    }
+  }
+
+  Value VisitExpr_(const LetNode* op) override {
+    auto value = Eval(op->value);
+    this->extend(op->var, value);
+    return Eval(op->body);
+  }
+
+  Value VisitExpr_(const TupleGetItemNode* op) override {
+    Value val = Eval(op->tuple);
+    auto product_node = val.as<TupleValueNode>();
+    CHECK(product_node)
+      << "interal error: when evaluating TupleGetItem expected a tuple value";
+    CHECK_LT(static_cast<size_t>(op->index), product_node->fields.size())
+      << "internal error: index out of bounds";
+    return product_node->fields[op->index];
+  }
+
+  Value VisitExpr_(const IfNode* op) override {
+    Value v = Eval(op->cond);
+    if (const TensorValueNode* bv = v.as<TensorValueNode>()) {
+      // TODO(@jroesch, @MK): Refactor code into helper from DCE.
+      if (reinterpret_cast<uint8_t*>(bv->data->data)[0]) {
+        return Eval(op->true_branch);
+      } else {
+        return Eval(op->false_branch);
+      }
+    } else {
+      throw EvalError("type error, type system should have caught this");
+    }
+  }
+};
+
+Interpreter::OpMap CompileOperators(const Environment& env, const Expr& e) {
+  Interpreter::OpMap op_map;
+  auto lowered_ops = LowerOps(env, e);
+  RELAY_LOG(INFO) << "LoweredFuncs: " << lowered_ops << std::endl;
+  if (lowered_ops.size()) {
+    const PackedFunc* fbuild_ptr = Registry::Get("relay.op.compiler._build");
+    CHECK(fbuild_ptr) << "Could not find registered function: relay.op.compiler._build";
+    auto fbuild = *fbuild_ptr;
+
+    // Collect the set of lowered functions to build a module.
+    Array<LoweredFunc> lowered_funcs;
+    for (auto lop : lowered_ops) {
+      lowered_funcs.push_back(lop->lowered_func);
+    }
+
+    Module module = fbuild(lowered_funcs);
+
+    // Loop over the lowered operations to map them into the operator map.
+    for (auto lop : lowered_ops) {
+      Function func = lop->func;
+      LoweredFunc lf = lop->lowered_func;
+
+      RELAY_LOG(INFO) << "LoweredFunc: " << lf->name << std::endl;
+      auto op_impl = module.GetFunction(lf->name);
+      op_map.insert({func, op_impl});
+    }
+  }
+
+  return op_map;
+}
+
+Value Evaluate(Environment env, Expr e) {
+  auto op_map = CompileOperators(env, e);
+  Interpreter interp(env, op_map);
+  return interp.Eval(e);
+}
+
+TVM_REGISTER_API("relay._interpreter.evaluate")
+    .set_body([](TVMArgs args, TVMRetValue* ret) {
+      Environment env = args[0];
+      Expr expr = args[1];
+      *ret = Evaluate(env, expr);
+    });
+
+}  // namespace relay
+}  // namespace tvm
diff --git a/src/relay/ir/base.cc b/src/relay/ir/base.cc
index a68910e56b71..1f73f297f99a 100644
--- a/src/relay/ir/base.cc
+++ b/src/relay/ir/base.cc
@@ -66,3 +66,5 @@ TVM_STATIC_IR_FUNCTOR_REGISTER(IRPrinter, vtable)
 
 }  // namespace relay
 }  // namespace tvm
+
+
diff --git a/src/relay/ir/environment.cc b/src/relay/ir/environment.cc
index dddad82c8afc..262758ba0478 100644
--- a/src/relay/ir/environment.cc
+++ b/src/relay/ir/environment.cc
@@ -49,9 +49,16 @@ void EnvironmentNode::Add(const GlobalVar& var,
         << "Environment#update changes type, not possible in this mode.";
   }
   this->functions.Set(var, checked_func);
-  // set gloval var map
-  CHECK(!global_var_map_.count(var->name_hint))
-      << "Duplicate global function name " << var->name_hint;
+
+  auto it = global_var_map_.find(var->name_hint);
+  if (it != global_var_map_.end()) {
+    CHECK_EQ((*it).second, var);
+  } else {
+    // set global var map
+    CHECK(!global_var_map_.count(var->name_hint))
+        << "Duplicate global function name " << var->name_hint;
+  }
+
   global_var_map_.Set(var->name_hint, var);
 }
 
@@ -94,7 +101,7 @@ TVM_REGISTER_API("relay._make.Environment")
 TVM_REGISTER_API("relay._env.Environment_Add")
 .set_body([](TVMArgs args, TVMRetValue *ret) {
     Environment env = args[0];
-    env->Add(args[1], args[2], false);
+    env->Add(args[1], args[2], args[3]);
   });
 
 TVM_REGISTER_API("relay._env.Environment_GetGlobalVar")
diff --git a/src/relay/ir/expr.cc b/src/relay/ir/expr.cc
index c75c414c8ce9..993892a94861 100644
--- a/src/relay/ir/expr.cc
+++ b/src/relay/ir/expr.cc
@@ -26,7 +26,10 @@ TVM_REGISTER_API("relay._make.Constant")
 
 TVM_STATIC_IR_FUNCTOR_REGISTER(IRPrinter, vtable)
 .set_dispatch<ConstantNode>([](const ConstantNode* node, tvm::IRPrinter* p) {
-    p->stream << "Constant(TODO)";
+    const PackedFunc* fprint = Registry::Get("relay._constant_repr");
+    CHECK(fprint) << "unable to find printing function for constants";
+    std::string data = (*fprint)(GetRef<Constant>(node));
+    p->stream << "Constant(" << data << ")";
   });
 
 TensorType ConstantNode::tensor_type() const {
@@ -104,12 +107,14 @@ TVM_STATIC_IR_FUNCTOR_REGISTER(IRPrinter, vtable)
 Function FunctionNode::make(tvm::Array<Var> params,
                             Expr body,
                             Type ret_type,
-                            tvm::Array<TypeVar> type_params) {
+                            tvm::Array<TypeVar> type_params,
+                            tvm::Attrs attrs) {
   NodePtr<FunctionNode> n = make_node<FunctionNode>();
   n->params = std::move(params);
   n->body = std::move(body);
   n->ret_type = std::move(ret_type);
   n->type_params = std::move(type_params);
+  n->attrs = std::move(attrs);
   return Function(n);
 }
 
@@ -121,6 +126,39 @@ FuncType FunctionNode::func_type_annotation() const {
   return FuncTypeNode::make(param_types, this->ret_type, this->type_params, {});
 }
 
+NodeRef FunctionGetAttr(const Function& func, const std::string& key) {
+  if (!func->attrs.defined()) { return NodeRef(); }
+
+  const DictAttrsNode* dict_attrs = func->attrs.as<DictAttrsNode>();
+  CHECK(dict_attrs);
+  auto it = dict_attrs->dict.find(key);
+  if (it != dict_attrs->dict.end()) {
+    return (*it).second;
+  } else {
+    return NodeRef();
+  }
+}
+
+Function FunctionSetAttr(const Function& func, const std::string& key, const NodeRef& data) {
+  const DictAttrsNode* dattrs = func->attrs.as<DictAttrsNode>();
+  Attrs func_attrs;
+  if (dattrs) {
+    Map<std::string, NodeRef> dict = dattrs->dict;
+    dict.Set(key, data);
+    func_attrs = DictAttrsNode::make(dict);
+  } else {
+    Map<std::string, NodeRef> dict = {{key, data}};
+    func_attrs = DictAttrsNode::make(dict);
+  }
+
+  return FunctionNode::make(
+    func->params,
+    func->body,
+    func->ret_type,
+    func->type_params,
+    func_attrs);
+}
+
 TVM_REGISTER_NODE_TYPE(FunctionNode);
 
 TVM_REGISTER_API("relay._make.Function")
@@ -132,7 +170,8 @@ TVM_STATIC_IR_FUNCTOR_REGISTER(IRPrinter, vtable)
 .set_dispatch<FunctionNode>([](const FunctionNode* node,
                                    tvm::IRPrinter* p) {
       p->stream << "FunctionNode(" << node->params << ", " << node->ret_type
-                << ", " << node->body << ", " << node->type_params << ")";
+                << ", " << node->body << ", " << node->type_params << ", "
+                << node->attrs << ")";
 });
 
 Call CallNode::make(Expr op, Array<Expr> args, Attrs attrs,
diff --git a/src/relay/ir/expr_functor.cc b/src/relay/ir/expr_functor.cc
index b7a752d43a5c..d0151f870f05 100644
--- a/src/relay/ir/expr_functor.cc
+++ b/src/relay/ir/expr_functor.cc
@@ -92,7 +92,7 @@ Expr ExprMutator::VisitExpr_(const FunctionNode* op) {
       body.same_as(op->body)) {
     return GetRef<Expr>(op);
   } else {
-    return FunctionNode::make(params, body, ret_type, ty_params);
+    return FunctionNode::make(params, body, ret_type, ty_params, op->attrs);
   }
 }
 
@@ -194,6 +194,7 @@ void ExprVisitor::ExprVisitor::VisitExpr_(const FunctionNode* op) {
 
 void ExprVisitor::VisitExpr_(const CallNode* op) {
   this->VisitExpr(op->op);
+
   for (auto ty_arg : op->type_args) {
     this->VisitType(ty_arg);
   }
diff --git a/src/relay/ir/hash.cc b/src/relay/ir/hash.cc
index ce2049f269df..4fd91256db9c 100644
--- a/src/relay/ir/hash.cc
+++ b/src/relay/ir/hash.cc
@@ -285,11 +285,11 @@ class RelayHashHandler:
   int var_counter = 0;
 };
 
-size_t StructuralHash(const Type& type) {
+size_t StructuralHash::operator()(const Type& type) const {
   return RelayHashHandler().TypeHash(type);
 }
 
-size_t StructuralHash(const Expr& expr) {
+size_t StructuralHash::operator()(const Expr& expr) const {
   return RelayHashHandler().ExprHash(expr);
 }
 
diff --git a/src/relay/pass/fuse_ops.cc b/src/relay/pass/fuse_ops.cc
new file mode 100644
index 000000000000..3aea12931649
--- /dev/null
+++ b/src/relay/pass/fuse_ops.cc
@@ -0,0 +1,86 @@
+/*!
+ * Copyright (c) 2018 by Contributors
+ *
+ * \file src/tvm/relay/pass/fuse_ops.cc
+ *
+ * \brief Fuse Relay eligble sequences of Relay operators into a single one.
+ *
+ */
+#include <tvm/relay/pass.h>
+#include <tvm/runtime/module.h>
+#include <tvm/lowered_func.h>
+#include <tvm/operation.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/logging.h>
+#include "../ir/type_functor.h"
+
+namespace tvm {
+namespace relay {
+
+using namespace runtime;
+
+struct AbstractFusableOps : ExprMutator {
+  Environment env;
+  Array<GlobalVar> fusable_funcs;
+  int counter = 0;
+  size_t expr_hash;
+
+  AbstractFusableOps(Environment env, size_t expr_hash) : env(env), expr_hash(expr_hash) {}
+
+  Expr VisitExpr_(const CallNode* call) {
+    if (auto op_node = call->op.as<OpNode>()) {
+      // Placeholder fusion algorithm which abstracts
+      // single definitions into functions only.
+      Array<Var> params;
+      Array<Expr> inner_args;
+      Array<Expr> args;
+
+      int param_number = 0;
+      for (auto arg : call->args) {
+        auto name = std::string("p") + std::to_string(param_number++);
+        auto type = arg->checked_type();
+        auto var = VarNode::make(name, type);
+        params.push_back(var);
+        inner_args.push_back(var);
+        args.push_back(VisitExpr(arg));
+      }
+
+      auto body = CallNode::make(call->op, inner_args, call->attrs);
+      auto func = FunctionNode::make(params, body, call->checked_type(), {});
+      func = FunctionSetAttr(func, "Primitive", tvm::Integer(1));
+      std::string func_name = "fused_";
+      func_name += op_node->name;
+      func_name += "_";
+      func_name += std::to_string(counter++);
+      func_name += "_";
+      func_name += std::to_string(expr_hash);
+      auto gv = GlobalVarNode::make(func_name);
+      env->Add(gv, func);
+      fusable_funcs.push_back(gv);
+      return CallNode::make(gv, args, Attrs());
+    } else {
+      return ExprMutator::VisitExpr_(call);
+    }
+  }
+};
+
+Expr FuseOps(const Environment& env, const Expr& e) {
+  // First we convert all chains of fusable ops into
+  // abstracted functions which we mark as primtive
+  // then we convert these primtive functions into
+  // new operators.
+  auto abstract = AbstractFusableOps(env, StructuralHash()(e));
+  auto abstracted_e = abstract.VisitExpr(e);
+  RELAY_LOG(INFO) << "FuseOps: before=" << e
+                  << "Fuse: after=" << abstracted_e;
+  return abstracted_e;
+}
+
+TVM_REGISTER_API("relay._ir_pass.FuseOps")
+.set_body([](TVMArgs args, TVMRetValue *ret) {
+    *ret = FuseOps(args[1], args[0]);
+});
+
+
+}  // namespace relay
+}  // namespace tvm
diff --git a/src/relay/pass/lower_ops.cc b/src/relay/pass/lower_ops.cc
new file mode 100644
index 000000000000..6bab9a924269
--- /dev/null
+++ b/src/relay/pass/lower_ops.cc
@@ -0,0 +1,222 @@
+/*!
+ * Copyright (c) 2018 by Contributors
+ *
+ * \file src/tvm/relay/pass/lower_ops.cc
+ *
+ * \brief Lower a Relay program to set of TVM operators.
+ *
+ */
+#include <tvm/lowered_func.h>
+#include <tvm/operation.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/logging.h>
+#include <tvm/relay/pass.h>
+#include <tvm/runtime/module.h>
+#include <tvm/relay/build_module.h>
+#include "../ir/type_functor.h"
+
+namespace tvm {
+namespace relay {
+
+using namespace runtime;
+
+LoweredOp LoweredOpNode::make(Function func, LoweredFunc lowered_func) {
+  auto node = make_node<LoweredOpNode>();
+  node->func = func;
+  node->lowered_func = lowered_func;
+  return LoweredOp(node);
+}
+
+struct AbstractLocalFunctions : ExprMutator {
+  Environment env;
+  size_t expr_hash;
+  int counter = 0;
+  std::unordered_set<GlobalVar, NodeHash, NodeEqual> visited_funcs;
+  explicit AbstractLocalFunctions(Environment env)
+      : env(env), expr_hash(0), counter(0), visited_funcs() {}
+
+  Expr Abstract(const Expr& e) {
+    expr_hash = StructuralHash()(e);
+    return VisitExpr(e);
+  }
+
+  Expr VisitExpr_(const GlobalVarNode* gvar_node) final {
+    auto gvar = GetRef<GlobalVar>(gvar_node);
+    auto it = visited_funcs.find(gvar);
+    if (it == visited_funcs.end()) {
+      auto func = env->Lookup(gvar);
+      visited_funcs.insert(gvar);
+      auto new_func = FunctionNode::make(
+        func->params,
+        VisitExpr(func->body),
+        func->ret_type,
+        func->type_params,
+        func->attrs);
+      env->Update(gvar, new_func);
+    }
+    return gvar;
+  }
+
+  Expr VisitExpr_(const FunctionNode* func_node) final {
+    Function func = GetRef<Function>(func_node);
+    auto free_vars = FreeVars(func);
+    Array<Var> params;
+    for (auto free_var : free_vars) {
+      auto var = VarNode::make("free_var", free_var->checked_type());
+      params.push_back(var);
+    }
+    std::string abs_func = "abstracted_func_";
+    abs_func += std::to_string(counter++);
+    abs_func += std::to_string(expr_hash);
+    auto gv = GlobalVarNode::make(abs_func);
+    auto lifted_func = FunctionNode::make(params, func, Type(), {}, {});
+    env->Add(gv, lifted_func);
+    Array<Expr> args;
+    for (auto free_var : free_vars) {
+      args.push_back(free_var);
+    }
+    return CallNode::make(gv, args, {});
+  }
+};
+
+struct LiveFunctions : ExprVisitor {
+  Environment env;
+  explicit LiveFunctions(Environment env) : env(env), global_funcs() {}
+
+  std::unordered_set<GlobalVar, NodeHash, NodeEqual> visited_funcs;
+  std::unordered_set<GlobalVar, NodeHash, NodeEqual> global_funcs;
+
+  void Live(const Expr& e) {
+    CHECK(!e.as<FunctionNode>())
+        << "functions should of been transformed away by previous pass";
+    VisitExpr(e);
+  }
+
+  void VisitExpr_(const FunctionNode* func_node) {
+    LOG(FATAL) << "functions should of been transformed away by previous pass";
+  }
+
+  void VisitExpr_(const GlobalVarNode* var_node) final {
+    GlobalVar var = GetRef<GlobalVar>(var_node);
+    auto it = visited_funcs.find(var);
+    if (it == visited_funcs.end()) {
+      auto func = env->Lookup(var);
+      visited_funcs.insert(var);
+      // The last pass has trasnformed functions of the form:
+      //
+      // let x = fn (p_1, ..., p_n) { ... };
+      // ...
+      //
+      // into, a top-level declaration:
+      //
+      // def abs_f(fv_1, ..., fv_n) {
+      //    return (fn (p_1...,p_N) { ... };)
+      // }
+      //
+      // and:
+      //
+      // let x = abs_f(fv_1, ... fv_n);
+      //
+      // The only other case we can handle is
+      //
+      // fn foo(...) { body }
+      //
+      // We just search through the body in this case.
+      if (auto inner_func = func->body.as<FunctionNode>()) {
+        return VisitExpr(inner_func->body);
+      } else {
+        return VisitExpr(func->body);
+      }
+    }
+  }
+
+  void VisitExpr_(const CallNode* call) final {
+    RELAY_LOG(INFO) << "LiveOps: CallNode=" << GetRef<Call>(call);
+    if (auto gv_node = call->op.as<GlobalVarNode>()) {
+      GlobalVar gvar = GetRef<GlobalVar>(gv_node);
+      Function func = env->Lookup(gvar);
+
+      auto attr = FunctionGetAttr(func, "Primitive");
+
+      if (attr.defined() && Downcast<Integer>(attr)->value == 1) {
+        global_funcs.insert(gvar);
+      } else {
+         VisitExpr(gvar);
+      }
+
+      // Finally we need to ensure to visit all the args no matter what.
+      for (auto arg : call->args) {
+        VisitExpr(arg);
+      }
+    } else {
+      return ExprVisitor::VisitExpr_(call);
+    }
+  }
+};
+
+using FCompute = TypedPackedFunc<Array<Tensor>(
+    const Attrs&, const Array<Tensor>&, Type, std::string)>;
+using FSchedule = TypedPackedFunc<Schedule(const Array<Tensor>&, std::string)>;
+
+/*! \brief Return the set of operators in their TVM format. */
+Array<LoweredOp> LowerOps(const Environment& env, const Expr& e,
+                          const std::string& target) {
+  RELAY_LOG(INFO) << "LowerOps: e=" << e;
+  auto flower_ptr = Registry::Get("relay.op.compiler._lower");
+  CHECK(flower_ptr);
+  PackedFunc flower = *flower_ptr;
+
+  auto abstracted_e = AbstractLocalFunctions(env).Abstract(e);
+  auto live_funcs = LiveFunctions(env);
+  live_funcs.VisitExpr(abstracted_e);
+
+  auto schedule_reg = Op::GetAttr<FSchedule>("FTVMSchedule");
+  auto compute_reg = Op::GetAttr<FCompute>("FTVMCompute");
+
+  Array<LoweredOp> lowered_funcs;
+
+  for (auto func_name : live_funcs.global_funcs) {
+    auto func = env->Lookup(func_name);
+    auto call = Downcast<Call>(func->body);
+    auto op_node = call->op.as<OpNode>();
+    CHECK(op_node) << "violated invariant that primtiive calls contain a single op call";
+    auto op = GetRef<Op>(op_node);
+    RELAY_LOG(INFO) << "LowerOps: Lowering " << op->name;
+
+    CHECK(IsPrimitiveOp(op)) << "failed to lower "
+      << op->name << "can only lower primitve operations";
+
+    Array<Tensor> inputs;
+    std::string input_name = "in";
+    int i = 0;
+    for (auto type_arg : call->type_args) {
+      auto tt = Downcast<TensorType>(type_arg);
+      inputs.push_back(PlaceholderOpNode::make(input_name + std::to_string(i),
+                                               tt->shape, tt->dtype)
+                           .output(0));
+      i++;
+    }
+
+    auto output_tt = op->op_type->ret_type;
+    Array<Tensor> outputs =
+        compute_reg[op](call->attrs, inputs, output_tt, target);
+    auto schedule = schedule_reg[op](outputs, target);
+    size_t hash = StructuralHash()(func);
+    LoweredFunc lf =
+        flower(op->name + std::to_string(hash), schedule, inputs, outputs);
+    func = FunctionSetAttr(func, "LoweredFunc", lf);
+    env->Add(func_name, func, true);
+    lowered_funcs.push_back(LoweredOpNode::make(func, lf));
+  }
+
+  return lowered_funcs;
+}
+
+TVM_REGISTER_API("relay._ir_pass.LowerOps")
+.set_body([](TVMArgs args, TVMRetValue *ret) {
+    *ret = LowerOps(args[0], args[1], args[2]);
+});
+
+
+}  // namespace relay
+}  // namespace tvm
diff --git a/src/relay/pass/type_infer.cc b/src/relay/pass/type_infer.cc
index c0f1db97b538..6aed93e511ed 100644
--- a/src/relay/pass/type_infer.cc
+++ b/src/relay/pass/type_infer.cc
@@ -272,8 +272,8 @@ class TypeInferencer : private ExprFunctor<Type(const Expr&)> {
     auto* fn_ty_node = ftype.as<FuncTypeNode>();
 
     CHECK(fn_ty_node != nullptr)
-        << "only expressions with function types can be called, at "
-        << call->span;
+        << "only expressions with function types can be called, found "
+        << ftype << " at " << call->span;
 
     Array<Type> type_args;
     FuncType fn_ty = Instantiate(fn_ty_node, &type_args);
@@ -479,12 +479,16 @@ Expr TypeInferencer::Infer(Expr expr) {
   // Step 1: Solve the constraints.
   solver_.Solve();
   // Step 2: Attach resolved types to checked_type field.
-  return Resolver(type_map_, &solver_).VisitExpr(expr);
+  auto resolved_expr = Resolver(type_map_, &solver_).VisitExpr(expr);
+  CHECK(WellFormed(resolved_expr));
+  return resolved_expr;
 }
 
 
 Expr InferType(const Expr& expr, const Environment& env) {
-  return TypeInferencer(env).Infer(expr);
+  auto e = TypeInferencer(env).Infer(expr);
+  CHECK(WellFormed(e));
+  return e;
 }
 
 Function InferType(const Function& func,
@@ -496,6 +500,7 @@ Function InferType(const Function& func,
   Expr func_ret = TypeInferencer(env).Infer(func_copy);
   auto map_node = env->functions.CopyOnWrite();
   map_node->data.erase(var.node_);
+  CHECK(WellFormed(func_ret));
   return Downcast<Function>(func_ret);
 }
 
diff --git a/src/relay/pass/util.cc b/src/relay/pass/util.cc
index c1f00c7b65e0..51ef0377868f 100644
--- a/src/relay/pass/util.cc
+++ b/src/relay/pass/util.cc
@@ -3,7 +3,7 @@
  *
  * \file util.cc
  *
- * \brief simple util for relay.
+ * \brief Utility functions for Relay.
  */
 #include <tvm/relay/pass.h>
 #include <tvm/relay/expr_functor.h>
diff --git a/tests/python/relay/test_graph_runtime.py b/tests/python/relay/test_graph_runtime.py
new file mode 100644
index 000000000000..1e55f890e514
--- /dev/null
+++ b/tests/python/relay/test_graph_runtime.py
@@ -0,0 +1,80 @@
+import numpy as np
+
+from tvm import relay
+from tvm.relay.ir_pass import infer_type
+from tvm.relay.interpreter import evaluate
+from tvm.relay.graph_runtime_codegen import graph_evaluate
+from tvm.relay.scope_builder import ScopeBuilder
+from tvm.relay.op import add
+from tvm.relay.env import Environment
+
+# @tq, @jr should we put this in testing ns?
+def check_rts(env, expr, args, expected_result):
+    """
+    Check that evaluating `expr` applied to the arguments produces
+    `result` on both the evaluator and TVM runtime.
+
+    Parameters
+    ----------
+    expr:
+        The expression to evaluate
+
+    args: list of Expr
+        The arguments to supply the expr.
+
+    expected_result:
+        The expected result of running the expression.
+    """
+    eval_result = evaluate(env, expr, *args)
+    rts_result = graph_evaluate(env, expr, *args)
+    np.testing.assert_allclose(eval_result.asnumpy(), rts_result.asnumpy())
+
+def test_add_op_scalar():
+    """
+    Program:
+        fn (x, y) {
+            return x + y;
+        }
+    """
+    env = Environment()
+    x = relay.var('x', shape=())
+    y = relay.var('y', shape=())
+    func = relay.Function([x, y], add(x, y))
+    x_data = np.array(10.0, dtype='float32')
+    y_data = np.array(1.0, dtype='float32')
+    check_rts(env, func, [x_data, y_data], x_data + y_data)
+
+def test_add_op_tensor():
+    """
+    Program:
+        fn (x, y) {
+            return x + y;
+        }
+    """
+    env = Environment()
+    x = relay.var('x', shape=(10, 5))
+    y = relay.var('y', shape=(10, 5))
+    func = relay.Function([x, y], add(x, y))
+    x_data = np.random.rand(10, 5).astype('float32')
+    y_data = np.random.rand(10, 5).astype('float32')
+    check_rts(env, func, [x_data, y_data], x_data + y_data)
+
+def test_add_op_broadcast():
+    """
+    Program:
+        fn (x, y) {
+            return x + y;
+        }
+    """
+    env = Environment()
+    x = relay.var('x', shape=(10, 5))
+    y = relay.var('y', shape=(1, 5))
+    func = relay.Function([x, y], add(x, y))
+    x_data = np.random.rand(10, 5).astype('float32')
+    y_data = np.random.rand(1, 5).astype('float32')
+    check_rts(env, func, [x_data, y_data], x_data + y_data)
+
+if __name__ == "__main__":
+    test_add_op_scalar()
+    test_add_op_tensor()
+    test_add_op_broadcast()
diff --git a/tests/python/relay/test_interpreter.py b/tests/python/relay/test_interpreter.py
new file mode 100644
index 000000000000..9a431b4c9524
--- /dev/null
+++ b/tests/python/relay/test_interpreter.py
@@ -0,0 +1,142 @@
+import numpy as np
+import tvm
+from tvm import relay
+from tvm.relay.interpreter import Value, TupleValue, evaluate
+from tvm.relay import op
+from tvm.relay.scope_builder import ScopeBuilder
+from tvm.relay import testing
+
+
+def check_eval(expr, args, expected_result, env=None, rtol=1e-07):
+    if env is None:
+        env = relay.env.Environment({})
+
+    result = evaluate(env, expr, *args)
+    np.testing.assert_allclose(result.asnumpy(), expected_result, rtol=rtol)
+
+
+def test_from_scalar():
+    np.testing.assert_allclose(Value.from_scalar(1, 'int32').asnumpy(), 1)
+    np.testing.assert_allclose(Value.from_scalar(10.0, 'float32').asnumpy(), 10.0)
+    np.testing.assert_allclose(Value.from_scalar(True).asnumpy(), True)
+
+
+def test_tuple_value():
+    tv = TupleValue(Value.from_scalar(
+        1), Value.from_scalar(2), Value.from_scalar(3))
+    np.testing.assert_allclose(tv[0].asnumpy(), 1)
+    np.testing.assert_allclose(tv[1].asnumpy(), 2)
+    np.testing.assert_allclose(tv[2].asnumpy(), 3)
+
+
+def test_id():
+    x = relay.var('x', 'float32')
+    ident = relay.Function([x], x)
+    env = relay.env.Environment({})
+    res = evaluate(env, ident, 1.0)
+    check_eval(ident, [1.0], 1.0)
+
+
+def test_add_const():
+    two = op.add(relay.const(1), relay.const(1))
+    func = relay.Function([], two)
+    check_eval(func, [], 2)
+
+
+def test_mul_param():
+    x = relay.var('x', shape=(10, 10))
+    y = relay.var('y', shape=(1, 10))
+    func = relay.Function([x, y], op.multiply(x, y))
+    x_data = np.random.rand(10, 10).astype('float32')
+    y_data = np.random.rand(1, 10).astype('float32')
+    check_eval(func, [x_data, y_data], x_data * y_data)
+
+
+# failing due to numeric issues
+
+# def test_dense():
+#     x = relay.var('x', shape=(10, 10))
+#     w = relay.var('w', shape=(10, 10))
+#     y = op.nn.dense(x, w)
+#     func = relay.Function([x, w], y)
+#     x_data = np.random.rand(10, 10).astype('float32')
+#     w_data = np.random.rand(10, 10).astype('float32')
+#     check_eval(func, [x_data, w_data], x_data @ w_data, rtol=0.1)
+
+# def test_linear():
+#     x = relay.var('x', shape=(10, 10))
+#     w = relay.var('w', shape=(10, 10))
+#     b = relay.var('b', shape=(10,))
+#     y = op.add(op.nn.dense(x, w), b)
+#     func = relay.Function([x, w, b], y)
+#     x_data = np.random.rand(10, 10).astype('float32')
+#     w_data = np.random.rand(10, 10).astype('float32')
+#     b_data = np.random.rand(10).astype('float32')
+#     check_eval(func, [x_data, w_data, b_data], x_data @ w_data + b_data)
+
+def test_equal():
+    i = relay.var('i', shape=[], dtype='int32')
+    j = relay.var('i', shape=[], dtype='int32')
+    z = op.equal(i, j)
+    func = relay.Function([i, j], z, ret_type=relay.TensorType([], 'bool'))
+    i_data = relay.const(0)
+    j_data = relay.const(0)
+    check_eval(func, [i_data, j_data], True)
+
+def test_subtract():
+    i = relay.var('i', shape=[], dtype='int32')
+    sub = op.subtract(i, relay.const(1, dtype='int32'))
+    func = relay.Function([i], sub, ret_type=relay.TensorType([], 'int32'))
+    i_data = np.array(1, dtype='int32')
+    check_eval(func, [i_data], 0)
+
+def test_simple_loop():
+    env = relay.env.Environment({})
+    sum_up = relay.GlobalVar('sum_up')
+    i = relay.var('i', shape=[], dtype='int32')
+    sb = ScopeBuilder()
+    with sb.if_scope(op.equal(i, relay.const(0, dtype='int32'))):
+        sb.ret(i)
+    with sb.else_scope():
+        one_less = op.subtract(i, relay.const(1, dtype='int32'))
+        rec_call = relay.Call(sum_up, [one_less])
+        sb.ret(op.add(rec_call, i))
+    func = relay.Function([i], sb.get(), ret_type=relay.TensorType([], 'int32'))
+    env[sum_up] = func
+    i_data = np.array(10, dtype='int32')
+    check_eval(sum_up, [i_data], sum(range(1, 11)), env=env)
+
+def test_loop():
+    env = relay.env.Environment({})
+    sum_up = relay.GlobalVar('sum_up')
+    i = relay.var('i', shape=[], dtype='int32')
+    accum = relay.var('accum', shape=[], dtype='int32')
+    sb = ScopeBuilder()
+    with sb.if_scope(op.equal(i, relay.const(0))):
+        sb.ret(accum)
+    with sb.else_scope():
+        one_less = op.subtract(i, relay.const(1))
+        new_accum = op.add(accum, i)
+        sb.ret(relay.Call(sum_up, [one_less, new_accum]))
+    func = relay.Function([i, accum], sb.get())
+    env[sum_up] = func
+    i_data = np.array(10, dtype='int32')
+    accum_data = np.array(0, dtype='int32')
+    check_eval(sum_up, [i_data, accum_data], sum(range(1, 11)), env=env)
+
+def test_mlp():
+    pass
+    # net = testing.mlp.get_workload(1)
+    # import pdb; pdb.set_trace()
+
+if __name__ == "__main__":
+    test_id()
+    test_add_const()
+    # test_dense()
+    # test_linear()
+    test_equal()
+    test_subtract()
+    test_simple_loop()
+    test_loop()
+    test_mlp()
+
diff --git a/tests/python/relay/test_type_infer.py b/tests/python/relay/test_type_infer.py
index b1823004022c..31d350dc7ff7 100644
--- a/tests/python/relay/test_type_infer.py
+++ b/tests/python/relay/test_type_infer.py
@@ -5,6 +5,16 @@
 import numpy as np
 from tvm.relay.ir_pass import infer_type
 from tvm import relay
+from tvm.relay import op
+from tvm.relay.scope_builder import ScopeBuilder
+
+
+def assert_has_type(expr, typ, env=relay.env.Environment({})):
+    checked_expr = infer_type(expr, env)
+    checked_type = checked_expr.checked_type
+    if checked_type != typ:
+        raise RuntimeError("Type mismatch %s vs %s" % (
+            checked_type, typ))
 
 
 def test_monomorphic_let():
@@ -16,6 +26,31 @@ def test_monomorphic_let():
     assert xchecked.checked_type == relay.scalar_type("float64")
 
 
+def test_single_op():
+    "Program: fn (x : float32) { let t1 = f(x); t1 }"
+    x = relay.var('x', shape=[])
+    func = relay.Function([x], op.log(x))
+    ttype = relay.TensorType([], dtype='float32')
+    assert_has_type(func, relay.FuncType([ttype], ttype))
+
+
+def test_add_broadcast_op():
+    """
+    Program:
+        fn (x: Tensor[(10, 4), f32], y: Tensor[(5, 10, 1), f32]) -> Tensor[(5, 10, 4), f32] {
+            return x + y;
+        }
+    """
+    pass
+    # x = relay.var('x', shape=(10, 4))
+    # y = relay.var('y', shape=(5, 10, 1))
+    # z = x + y
+    # func = relay.Function([x, y], z)
+    # ttype = relay.TensorType((5, 5, 5), 'float32')
+    # expected_ty = relay.FuncType([ttype, ttype], ttype)
+    # assert_has_type(func.to_func(), expected_ty)
+
+
 def test_dual_op():
     """Program:
        fn (x : Tensor[f32, (10, 10)]) {
@@ -41,7 +76,6 @@ def f(x : Tensor[(10, 10), f32]) {
            return log(x);
        }
     """
-    sb = relay.ScopeBuilder()
     tp = relay.TensorType((10, 10))
     x = relay.var("x", tp)
     f = relay.Function([x], relay.log(x))
@@ -76,6 +110,24 @@ def f(n: i32, data: f32) -> f32 {
     assert "%3 = @f(%1, %2)" in env.astext()
     assert env[f].checked_type == relay.FuncType([ti32, tf32], tf32)
 
+# This currently fails and should pass under the type system.
+#
+# This test is to illustrate problem with our weak form of
+# unification.
+#
+
+
+def test_incomplete_call():
+    sb = ScopeBuilder()
+    x = relay.var('x', dtype='int32')
+    f = relay.var('f')
+    func = relay.Function([x, f], relay.Call(f, [x]))
+
+    try:
+        relay.ir_pass.infer_type(func)
+        assert False
+    except tvm.TVMError as e:
+        assert True
 
 def test_tuple():
     tp = relay.TensorType((10,))
@@ -84,13 +136,13 @@ def test_tuple():
     assert (relay.ir_pass.infer_type(res).checked_type ==
             relay.TupleType([tp, tp]))
 
-
 def test_free_expr():
     x = relay.var("x", "float32")
     y = relay.add(x, x)
     yy = relay.ir_pass.infer_type(y)
     assert yy.checked_type == relay.scalar_type("float32")
 
+
 def test_type_args():
     x = relay.var("x", shape=(10, 10))
     y = relay.var("y", shape=(1, 10))
@@ -107,6 +159,7 @@ def test_type_args():
     assert sh2[0].value == 1
     assert sh2[1].value == 10
 
+
 def test_self_reference():
     """
     Program:
@@ -117,31 +170,41 @@ def f(x) {
     a = relay.TypeVar("a")
     x = relay.var("x", a)
     sb = relay.ScopeBuilder()
+
     f = relay.Function([x], x)
     fx = relay.Call(f, [x])
     assert relay.ir_pass.infer_type(x).checked_type == a
     assert relay.ir_pass.infer_type(f).checked_type == relay.FuncType([a], a)
     assert relay.ir_pass.infer_type(fx).checked_type == a
 
+
 def test_global_var_cow_issue():
     env = relay.env.Environment({})
     gv = relay.GlobalVar("foo")
     x = relay.var('x', shape=[])
-    func = relay.Function([x], relay.Call(gv, [x]), relay.TensorType([], 'float32'))
+    func = relay.Function([x], relay.Call(gv, [x]),
+                          relay.TensorType([], 'float32'))
     env[gv] = func
-    # They should both point to the same global variable if global variables are
-    # stable across type checking.
-    assert gv == func.body.op
+
+
+def test_equal():
+    i = relay.var('i', shape=[], dtype='int32')
+    eq = op.equal(i, relay.const(0, dtype='int32'))
+    # This should fail ....
+    func = relay.Function([i], eq, ret_type=relay.TensorType([], 'int32'))
+
 
 if __name__ == "__main__":
     test_free_expr()
     test_dual_op()
+    test_single_op()
     test_recursion()
     test_monomorphic_let()
     test_decl()
     test_recursion()
     test_tuple()
+    test_incomplete_call()
     test_free_expr()
     test_type_args()
     test_self_reference()
-    test_global_var_cow_issue()
\ No newline at end of file
+    test_global_var_cow_issue()
diff --git a/tests/scripts/task_python_integration.sh b/tests/scripts/task_python_integration.sh
index 818376717176..d11dcd5da71a 100755
--- a/tests/scripts/task_python_integration.sh
+++ b/tests/scripts/task_python_integration.sh
@@ -1,5 +1,5 @@
 #!/bin/bash
-export PYTHONPATH=python:apps/extension/python
+export PYTHONPATH=python:topi/python:apps/extension/python
 export LD_LIBRARY_PATH=build:${LD_LIBRARY_PATH}
 
 rm -rf python/tvm/*.pyc python/tvm/*/*.pyc python/tvm/*/*/*.pyc