ref: 4bdb0c1286e7999f0dda6df5160337c02bc089b3
parent: dda1943b64afc23dee860b4f058c7f182748b7f7
author: Lennart Augustsson <lennart@augustsson.net>
date: Thu Jan 9 05:19:08 EST 2025
Make sure type variables always point from new to old.
--- a/src/MicroHs/TypeCheck.hs
+++ b/src/MicroHs/TypeCheck.hs
@@ -745,9 +745,11 @@
unifyR :: HasCallStack =>
SLoc -> EType -> EType -> T ()
-unifyR _ (EVar x1) (EVar x2) | x1 == x2 = return ()
+unifyR _ (EVar x1) (EVar x2) | x1 == x2 = return ()
unifyR loc (EApp f1 a1) (EApp f2 a2) = do { unifyR loc f1 f2; unifyR loc a1 a2 }-unifyR _ (EUVar r1) (EUVar r2) | r1 == r2 = return ()
+unifyR loc t1@(EUVar r1) t2@(EUVar r2) | r1 < r2 = unifyVar loc r2 t1 -- always make higher
+ | r1 > r2 = unifyVar loc r1 t2 -- TRefs point to lower
+ | otherwise = return ()
unifyR loc (EUVar r1) t2 = unifyVar loc r1 t2
unifyR loc t1 (EUVar r2) = unifyVar loc r2 t1
unifyR loc t1 t2 = do