diff --git a/type_check.py b/type_check.py
new file mode 100644
index 0000000..f70cdc8
--- /dev/null
+++ b/type_check.py
@@ -0,0 +1,46 @@
+def is_variable(b):
+    return isinstance(b, str) and b.isupper()
+
+def unify(ctx, a, b):
+    """
+    a is the concrete type
+    b is the type with parameter
+    lower case means primitive type
+    upper case means type variable
+    list and tuples are just list and tuples
+    """
+    if isinstance(ctx, str):
+        return ctx
+
+    if is_variable(b):
+        if b in ctx:
+            b = ctx[b]
+        else:
+            ctx[b] = a
+            return ctx
+
+    if isinstance(a, list) and isinstance(b, list):
+        return unify(ctx, a[0], b[0])
+    elif isinstance(a, tuple) and isinstance(b, tuple) and len(a) == len(b):
+        old = ctx
+        for x, y in zip(a, b):
+            old = unify(old, x, y)
+        return old
+    else:
+        if a == b:
+            return ctx
+        else:
+            return f"{a} != {b}"
+
+def check_eq(a, b):
+    unifier = unify({}, a, b)
+    print(f"{a} <- {b}\n{unifier}\n")
+
+check_eq('a', 'A')
+check_eq(['a'], 'A')
+check_eq(['a'], ['A'])
+check_eq(['a'], ['b'])
+check_eq([('a', 'a', 'b')], ['A'])
+check_eq([('a', 'a', 'b')], [('A', 'A', 'B')])
+check_eq([('a', 'a', 'b')], [('A', 'A', 'A')])
+