diff --git a/build.sbt b/build.sbt
index 060ed5f..c354fde 100644
--- a/build.sbt
+++ b/build.sbt
@@ -52,6 +52,7 @@ lazy val root = (project in file(".")).
     // Dependencies
     libraryDependencies ++= Seq(
       scalaParserCombinators,
+      cats,
       scalaTest % Test,
       scalaCheck % Test
     ),
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 0dd0694..bebd634 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -4,4 +4,5 @@ object Dependencies {
   lazy val scalaTest = "org.scalatest" %% "scalatest" % "3.0.1"
   lazy val scalaCheck = "org.scalacheck" %% "scalacheck" % "1.13.4"
   lazy val scalaParserCombinators = "org.scala-lang.modules" %% "scala-parser-combinators" % "1.0.5"
+  lazy val cats = "org.typelevel" %% "cats" % "0.9.0"
 }
diff --git a/src/main/scala/edu/colorado/plv/cuanto/jsy/imp/Parser.scala b/src/main/scala/edu/colorado/plv/cuanto/jsy/imp/Parser.scala
new file mode 100644
index 0000000..282ce5a
--- /dev/null
+++ b/src/main/scala/edu/colorado/plv/cuanto/jsy/imp/Parser.scala
@@ -0,0 +1,6 @@
+package edu.colorado.plv.cuanto.jsy.imp
+
+import edu.colorado.plv.cuanto.jsy.common.UnitOpParser
+import edu.colorado.plv.cuanto.jsy.{mutation, numerical}
+
+object Parser extends UnitOpParser with mutation.ParserLike with numerical.ParserWithBindingLike
diff --git a/src/main/scala/edu/colorado/plv/cuanto/jsy/imp/package.scala b/src/main/scala/edu/colorado/plv/cuanto/jsy/imp/package.scala
new file mode 100644
index 0000000..738aa08
--- /dev/null
+++ b/src/main/scala/edu/colorado/plv/cuanto/jsy/imp/package.scala
@@ -0,0 +1,21 @@
+package edu.colorado.plv.cuanto.jsy
+
+import edu.colorado.plv.cuanto.jsy.binding.Mode
+
+package imp {
+
+  /** Mode `var`. Mutable variables.
+    *
+    * @group Abstract Syntax Nodes
+    */
+  case object MVar extends Mode
+
+}
+
+/** The Imp subset of JavaScripty.
+  *
+  * Mixes [[numerical]] and [[mutation]].
+  *
+  * @author Bor-Yuh Evan Chang
+  */
+package object imp
diff --git a/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/Parser.scala b/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/Parser.scala
index 0b18921..8cb1999 100644
--- a/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/Parser.scala
+++ b/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/Parser.scala
@@ -1,14 +1,15 @@
-package edu.colorado.plv.cuanto.jsy.mutation
+package edu.colorado.plv.cuanto.jsy
+package mutation
 
-import edu.colorado.plv.cuanto.jsy.common.{JsyParserLike, OpParserLike, UnitOpParser}
+import edu.colorado.plv.cuanto.jsy.common.{JsyParserLike, OpParserLike}
 
-trait ParserLike extends OpParserLike with JsyParserLike
+trait ParserLike extends OpParserLike with JsyParserLike {
+  abstract override def opAtom: Parser[Expr] =
+    positioned("null" ^^^ Null) |
+    super.opAtom
 
-/**
-  * @author Bor-Yuh Evan Chang
-  */
-object Parser extends UnitOpParser with ParserLike {
-  override val bop = ???
-  override def expr = ???
-  override def start = ???
+  lazy val mutationBop: OpPrecedence = List(
+    List("=" -> Assign)
+  )
 }
+
diff --git a/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/mem/Mem.scala b/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/mem/Mem.scala
new file mode 100644
index 0000000..2162539
--- /dev/null
+++ b/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/mem/Mem.scala
@@ -0,0 +1,41 @@
+package edu.colorado.plv.cuanto.jsy
+package mutation.mem
+
+import cats.data.State
+
+/** Address.
+  *
+  * @group Intermediate AST Nodes
+  */
+case class A private (a: Int) extends Val
+
+/** Memory.
+  *
+  * Memory is a mapping from addresses to values. It enforces the invariant that
+  * addresses are allocated in this module.
+  *
+  * @tparam V The value type stored in this memory
+  * @author Bor-Yuh Evan Chang
+  */
+class Mem[V] private (map: Map[A, V], nextAddr: Int) {
+  def apply(key: A): V = map(key)
+  def get(key: A): Option[V] = map.get(key)
+  def +(kv: (A, V)): Mem[V] = new Mem[V](map + kv, nextAddr)
+  def contains(key: A): Boolean = map.contains(key)
+  override def toString: String = map.toString
+
+  private def alloc(v: V): (Mem[V], A) = {
+    val fresha = A(nextAddr)
+    (new Mem[V](map + (fresha -> v), nextAddr + 1), fresha)
+  }
+}
+
+object Mem {
+  def empty[V]: Mem[V] = new Mem[V](Map.empty, 1)
+
+  /** Get a fresh address. */
+  def alloc[V](v: V): State[Mem[V], A] = State.get flatMap { m =>
+    val (mp, a) = m.alloc(v)
+    State.set(mp) map { _ => a }
+  }
+}
diff --git a/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/package.scala b/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/package.scala
index 1e9cd0d..7b8957b 100644
--- a/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/package.scala
+++ b/src/main/scala/edu/colorado/plv/cuanto/jsy/mutation/package.scala
@@ -11,12 +11,6 @@ package mutation {
   /** @group Intermediate AST Nodes */
   case object Deref extends Uop
 
-  /** Address.
-    *
-    * @group Intermediate AST Nodes
-    */
-  case class A private (a: Int) extends Val
-
 }
 
 
diff --git a/src/main/scala/edu/colorado/plv/cuanto/jsy/string/package.scala b/src/main/scala/edu/colorado/plv/cuanto/jsy/string/package.scala
index 19b9d17..22dcd7c 100644
--- a/src/main/scala/edu/colorado/plv/cuanto/jsy/string/package.scala
+++ b/src/main/scala/edu/colorado/plv/cuanto/jsy/string/package.scala
@@ -17,6 +17,6 @@ package object string {
   /** The string concatenation operator is syntactically overloaded as
     * [[edu.colorado.plv.cuanto.jsy.arithmetic.Plus]].
     */
-  val Concat: Bop = arithmetic.Plus
+  val Concat = arithmetic.Plus
 
 }
diff --git a/src/test/scala/edu/colorado/plv/cuanto/jsy/imp/ImpParserSpec.scala b/src/test/scala/edu/colorado/plv/cuanto/jsy/imp/ImpParserSpec.scala
new file mode 100644
index 0000000..a2bd3cd
--- /dev/null
+++ b/src/test/scala/edu/colorado/plv/cuanto/jsy/imp/ImpParserSpec.scala
@@ -0,0 +1,35 @@
+package edu.colorado.plv.cuanto.jsy
+package imp
+
+import edu.colorado.plv.cuanto.CuantoSpec
+import edu.colorado.plv.cuanto.jsy.arithmetic.N
+import edu.colorado.plv.cuanto.jsy.binding._
+import edu.colorado.plv.cuanto.jsy.boolean._
+import edu.colorado.plv.cuanto.jsy.common.ParserBehaviors
+import edu.colorado.plv.cuanto.jsy.mutation.Assign
+
+/**
+  * @author Bor-Yuh Evan Chang
+  */
+class ImpParserSpec extends CuantoSpec with ParserBehaviors {
+
+  override lazy val positives = Table(
+    "concrete" -> "abstract",
+    """{ let x = 3
+      |  var y = true
+      |  if (y) { x = 4 } else { x = 5 }
+      |}
+    """.stripMargin
+      -> Bind(MVar, Var("x"), N(3),
+        Bind(MVar, Var("y"), B(true),
+          If(Var("y"),
+            Binary(Assign, Var("x"), N(4)),
+            Binary(Assign, Var("x"), N(4))
+          )
+        )
+      )
+
+  )
+
+  "jsy.imp.Parser" should behave like parser(Parser.parse)
+}
\ No newline at end of file
diff --git a/src/test/scala/edu/colorado/plv/cuanto/jsy/mutation/MutationParserSpec.scala b/src/test/scala/edu/colorado/plv/cuanto/jsy/mutation/MutationParserSpec.scala
deleted file mode 100644
index 133ffc6..0000000
--- a/src/test/scala/edu/colorado/plv/cuanto/jsy/mutation/MutationParserSpec.scala
+++ /dev/null
@@ -1,16 +0,0 @@
-package edu.colorado.plv.cuanto.jsy.mutation
-
-import edu.colorado.plv.cuanto.CuantoSpec
-import edu.colorado.plv.cuanto.jsy.common.ParserBehaviors
-
-/**
-  * @author Bor-Yuh Evan Chang
-  */
-class MutationParserSpec extends CuantoSpec with ParserBehaviors {
-
-  override lazy val positives = Table(
-    "concrete" -> "abstract"
-  )
-
-  "jsy.objects.Parser" should behave like parser(Parser.parse)
-}
\ No newline at end of file