Document and fix code style

src/TypeChecker.hs

@@ -14,7 +14,6 @@ import           Grammar.Print        (Print (prt), concatD, doc, printTree,
 import           Prelude              hiding (exp, id)
 import qualified TypeCheckerIr        as T
 
-
 -- NOTE: this type checker is poorly tested
 
 -- TODO
@@ -22,8 +21,8 @@ import qualified TypeCheckerIr        as T
 -- Type inference
 
 data Cxt = Cxt
-  { env :: Map Ident Type
-  , sig :: Map Ident Type
+    { env :: Map Ident Type -- ^ Local scope signature
+    , sig :: Map Ident Type -- ^ Top-level signatures
     }
 
 initCxt :: [Bind] -> Cxt
@@ -34,30 +33,27 @@ initCxt sc = Cxt { env = mempty
 typecheck :: Program -> Err T.Program
 typecheck (Program sc) = T.Program <$> mapM (checkBind $ initCxt sc) sc
 
-
+-- | Check if infered rhs type matches type signature.
 checkBind :: Cxt -> Bind -> Err T.Bind
 checkBind cxt b =
     case expandLambdas b of
         Bind name t _ parms rhs -> do
             (rhs', t_rhs) <- infer cxt rhs
-
             unless (typeEq t_rhs t) . throwError $ typeErr name t t_rhs
-
             pure $ T.Bind (name, t) (zip parms ts_parms) rhs'
-
         where
           ts_parms = fst $ partitionType (length parms) t
 
+-- | @ f x y = rhs ⇒ f = \x.\y. rhs @
 expandLambdas :: Bind -> Bind
 expandLambdas (Bind name t _ parms rhs) = Bind name t name [] rhs'
   where
     rhs'     = foldr ($) rhs $ zipWith EAbs parms ts_parms
     ts_parms = fst $ partitionType (length parms) t
 
-
+-- | Infer type of expression.
 infer :: Cxt -> Exp -> Err (T.Exp, Type)
 infer cxt = \case
-
     EId x ->
         case lookupEnv x cxt of
             Nothing ->
@@ -99,6 +95,7 @@ infer cxt = \case
             throwError "Inferred type and type annotation doesn't match"
         pure (e', t1)
 
+-- | Check infered type matches the supplied type.
 check :: Cxt -> Exp -> Type -> Err T.Exp
 check cxt exp typ = case exp of
 
@@ -108,9 +105,7 @@ check cxt exp typ = case exp of
                            ("Unbound variable:" ++ printTree x)
                            (lookupSig x cxt)
             Just t -> pure t
-
         unless (typeEq t typ) . throwError $ typeErr x typ t
-
         pure $ T.EId (x, t)
 
     EInt i    -> do
@@ -147,14 +142,15 @@ check cxt exp typ = case exp of
             throwError "Inferred type and type annotation doesn't match"
         check cxt e t
 
-insertBind :: Bind -> Cxt -> Cxt
-insertBind (Bind n t _ _ _) = insertEnv n t
-
+-- | Check if types are equivalent. Doesn't handle coercion or polymorphism.
 typeEq :: Type -> Type -> Bool
 typeEq (TFun t t1) (TFun q q1) = typeEq t q && typeEq t1 q1
 typeEq t           t1          = t == t1
 
-partitionType :: Int -> Type -> ([Type], Type)
+-- | Partion type into types of parameters and return type.
+partitionType :: Int -- Number of parameters to apply
+              -> Type
+              -> ([Type], Type)
 partitionType = go []
   where
     go acc 0 t = (acc, t)
@@ -162,6 +158,9 @@ partitionType = go []
         TFun t1 t2 -> go (snoc t1 acc) (i - 1) t2
         _          -> error "Number of parameters and type doesn't match"
 
+insertBind :: Bind -> Cxt -> Cxt
+insertBind (Bind n t _ _ _) = insertEnv n t
+
 lookupEnv :: Ident -> Cxt -> Maybe Type
 lookupEnv x = Map.lookup x . env