Comments and layout only

diff --git a/compiler/types/Unify.lhs b/compiler/types/Unify.lhs
index 9d94a63..5a1dbbc 100644 (file)
--- a/compiler/types/Unify.lhs
+++ b/compiler/types/Unify.lhs
@@ -120,24 +120,26 @@ match :: MatchEnv -- For the most part this is pushed downwards
 -- it respects NewTypes and PredType
 
 match menv subst ty1 ty2 | Just ty1' <- tcView ty1 = match menv subst ty1' ty2
-match menv subst ty1 ty2 | Just ty2' <- tcView ty2 = match menv subst ty1 ty2'
+                         | Just ty2' <- tcView ty2 = match menv subst ty1 ty2'
 
 match menv subst (TyVarTy tv1) ty2
   | tv1 `elemVarSet` me_tmpls menv
   = case lookupVarEnv subst tv1' of
-       Nothing | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
-               -> Nothing      -- Occurs check
-               | not (typeKind ty2 `isSubKind` tyVarKind tv1)
-               -> Nothing      -- Kind mis-match
-               | otherwise
-               -> Just (extendVarEnv subst tv1 ty2)
-
-       Just ty1' | tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
+       Nothing         -- No existing binding
+           | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
+           -> Nothing  -- Occurs check
+           | not (typeKind ty2 `isSubKind` tyVarKind tv1)
+           -> Nothing  -- Kind mis-match
+           | otherwise
+           -> Just (extendVarEnv subst tv1 ty2)
+
+       Just ty1'       -- There is an existing binding; check whether ty2 matches it
+           | tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
                -- ty1 has no locally-bound variables, hence nukeRnEnvL
                -- Note tcEqType...we are doing source-type matching here
-                 -> Just subst
-
-       other -> Nothing
+           -> Just subst
+           | otherwise -> Nothing      -- ty2 doesn't match
+           
 
    | otherwise -- tv1 is not a template tyvar
    = case ty2 of
@@ -161,6 +163,7 @@ match menv subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
        ; match menv subst' ty1b ty2b }
 match menv subst (AppTy ty1a ty1b) ty2
   | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
+       -- 'repSplit' used because the tcView stuff is done above
   = do { subst' <- match menv subst ty1a ty2a
        ; match menv subst' ty1b ty2b }