Take a stab at typechecking.

src/Control/Abstract/Addressable.hs

@@ -48,6 +48,7 @@ letrec name body = do
 instance (MonadFail m, LocationFor value ~ Precise, MonadHeap value m) => MonadAddressable Precise value m where
   deref = derefWith (maybeM uninitializedAddress . unLatest)
   alloc _ = do
+    -- Compute the next available address in the heap, then write an empty value into it.
     addr <- fmap (Address . Precise . heapSize) getHeap
     addr <$ modifyHeap (heapInit addr mempty)
 

src/Control/Abstract/Value.hs

@@ -261,6 +261,9 @@ instance (Alternative m, MonadEnvironment Type m, MonadFail m, MonadFresh m, Mon
   rational _ = pure Type.Rational
   multiple   = pure . Type.Product
   array      = pure . Type.Array
+  klass _ _  = pure Object
+
+  objectEnvironment _ = pure mempty
 
   ifthenelse cond if' else' = unify cond Bool *> (if' <|> else')
 

src/Data/Abstract/Type.hs

@@ -20,6 +20,7 @@ data Type
   | Var TName      -- ^ A type variable.
   | Product [Type] -- ^ N-ary products.
   | Array [Type]   -- ^ Arrays. Note that this is heterogenous.
+  | Object         -- ^ Objects. Once we have some notion of inheritance we'll need to store a superclass.
   deriving (Eq, Ord, Show)
 
 -- TODO: À la carte representation of types.