diff --git a/compiler/keywords.py b/compiler/constants.py
similarity index 95%
rename from compiler/keywords.py
rename to compiler/constants.py
index f4c9511..a67c81f 100644
--- a/compiler/keywords.py
+++ b/compiler/constants.py
@@ -1,4 +1,4 @@
-from enum import IntFlag,auto
+from enum import IntFlag,auto,Enum
 
 class PrintableFlag(IntFlag):
   def __repr__(self):
@@ -106,3 +106,9 @@ class Token(PrintableFlag):
   STRINGCONSTANT = Atom.STRINGCONSTANT.value
   SYMBOL = auto()
   KEYWORD = auto()
+
+class SymbolType(Enum):
+  STATIC = auto()
+  FIELD = auto()
+  ARG = auto()
+  VAR = auto()
\ No newline at end of file
diff --git a/compiler/engine.py b/compiler/engine.py
index 5eb3e03..1328610 100644
--- a/compiler/engine.py
+++ b/compiler/engine.py
@@ -1,5 +1,5 @@
 from tokenizer import JackTokenizer
-from keywords import *
+from constants import *
 from grammar import *
 import sys
 
diff --git a/compiler/grammar.py b/compiler/grammar.py
index f1e1f18..ba18368 100644
--- a/compiler/grammar.py
+++ b/compiler/grammar.py
@@ -1,4 +1,4 @@
-from keywords import Atom
+from constants import Atom
 
 """
 The grammar is defined by the following constructs:
diff --git a/compiler/__init__.py b/compiler/main.py
similarity index 72%
rename from compiler/__init__.py
rename to compiler/main.py
index 975db70..1f00d62 100644
--- a/compiler/__init__.py
+++ b/compiler/main.py
@@ -2,12 +2,11 @@ from engine import Engine
 import sys
 from pathlib import Path
 
-if __name__ == '__main__':
+if __name__ == '__main__' and len(sys.argv) > 1:
   p = Path(sys.argv[1])
   if p.is_dir():
     for f in p.glob("*.jack"):
       print("compiling %s" % f)
       Engine(f.as_posix()).compileClass()
   elif p.is_file():
-    Engine(p.as_posix()).compileClass()
-
+    Engine(p.as_posix()).compileClass()
\ No newline at end of file
diff --git a/compiler/symboltable.py b/compiler/symboltable.py
new file mode 100644
index 0000000..f417231
--- /dev/null
+++ b/compiler/symboltable.py
@@ -0,0 +1,48 @@
+from constants import SymbolType
+
+class SymbolTable:
+  def __init__(self):
+    self.subroutineTable = {}
+    self.classTable = {}
+    self.subroutineIndex = 0
+    self.classIndex = 0
+
+  def startSubroutine(self):
+    self.subroutineTable = {}
+
+  def define(self, name, var_type, kind):
+    if (kind in [SymbolType.STATIC, SymbolType.FIELD]):
+      self.classTable[name] = (var_type, kind, self.classIndex)
+      self.classIndex += 1
+    elif (kind in [SymbolType.ARG, SymbolType.VAR]):
+      self.subroutineTable[name] = (var_type, kind, self.subroutineIndex)
+      self.subroutineIndex += 1
+    else:
+      raise Exception("Invalid SymbolType")
+
+  def varCount(self, kind):
+    t = None
+    if (kind in [SymbolType.STATIC, SymbolType.FIELD]):
+      t = self.classTable
+    elif (kind in [SymbolType.ARG, SymbolType.VAR]):
+      t = self.subroutineTable
+    else:
+      raise Exception("Invalid SymbolType")
+    return len([i for i in t.values() if i[1] == kind])
+
+  def _lookup(self, name, index):
+    if name in self.classTable:
+      return self.classTable[name][index]
+    elif name in self.subroutineTable:
+      return self.subroutineTable[name][index]
+    else:
+      raise Exception("Invalid variable name")
+
+  def TypeOf(self, name):
+    return self._lookup(name, 0)
+
+  def KindOf(self, name):
+    return self._lookup(name, 1)
+
+  def IndexOf(self, name):
+    return self._lookup(name, 2)
diff --git a/compiler/symboltable_test.py b/compiler/symboltable_test.py
new file mode 100644
index 0000000..7a92009
--- /dev/null
+++ b/compiler/symboltable_test.py
@@ -0,0 +1,53 @@
+from symboltable import SymbolTable
+from constants import SymbolType
+def test_st_init():
+  st = SymbolTable()
+  assert(st.subroutineTable == {})
+  assert(st.classTable == {})
+
+def test_st_define():
+  st = SymbolTable()
+  st.define("first", "int", SymbolType.STATIC)
+  st.define("second", "SomeClass", SymbolType.FIELD)
+  st.define("third", "String", SymbolType.ARG)
+  st.define("fourth", "bool", SymbolType.VAR)
+
+  assert(st.classTable == {
+    "first": ("int", SymbolType.STATIC, 0),
+    "second": ("SomeClass", SymbolType.FIELD, 1),
+  })
+
+  assert(st.subroutineTable == {
+    "third": ("String", SymbolType.ARG, 0),
+    "fourth": ("bool", SymbolType.VAR, 1),
+  })
+
+def test_subroutine():
+  st = SymbolTable()
+  st.define("first", "int", SymbolType.ARG)
+  st.startSubroutine()
+  assert(st.subroutineTable == {})
+
+def test_var_count():
+  st = SymbolTable()
+  st.define("first", "int", SymbolType.STATIC)
+  st.define("second", "SomeClass", SymbolType.FIELD)
+  st.define("third", "String", SymbolType.ARG)
+  st.define("fourth", "bool", SymbolType.VAR)
+
+  assert(st.varCount(SymbolType.STATIC) == 1)
+  assert(st.varCount(SymbolType.FIELD) == 1)
+  assert(st.varCount(SymbolType.ARG) == 1)
+  assert(st.varCount(SymbolType.VAR) == 1)
+
+def test_lookups():
+  st = SymbolTable()
+  st.define("first", "int", SymbolType.STATIC)
+  st.define("second", "SomeClass", SymbolType.FIELD)
+  st.define("third", "String", SymbolType.ARG)
+  st.define("fourth", "bool", SymbolType.VAR)
+
+  assert(st.KindOf("first") == SymbolType.STATIC)
+  assert(st.TypeOf("second") == "SomeClass")
+  assert(st.IndexOf("third") == 0)
+  assert(st.IndexOf("fourth") == 1)
\ No newline at end of file
diff --git a/compiler/tokenizer.py b/compiler/tokenizer.py
index 076d406..7d20110 100644
--- a/compiler/tokenizer.py
+++ b/compiler/tokenizer.py
@@ -1,5 +1,5 @@
 import re
-from keywords import *
+from constants import *
 from html import escape
 from enum import Enum
 # Superclass in some sense