From 1ac7ba99fc809958ab59ed9b81df6fda7f2dbf05 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Mon, 27 Jul 2020 08:35:57 +0200
Subject: Correct type variable rigidity (I think)

---
 typecheck/CC/Typecheck.hs       | 12 ++++++++++++
 typecheck/CC/Typecheck/Types.hs |  3 +--
 2 files changed, 13 insertions(+), 2 deletions(-)

(limited to 'typecheck')

diff --git a/typecheck/CC/Typecheck.hs b/typecheck/CC/Typecheck.hs
index 824a714..292eaeb 100644
--- a/typecheck/CC/Typecheck.hs
+++ b/typecheck/CC/Typecheck.hs
@@ -146,6 +146,14 @@ instantiate (T.TypeScheme bnds ty) = do
 freshenFrees :: Env -> T.Type -> TM T.Type
 freshenFrees env = instantiate . generalise env
 
+replaceRigid :: T.Type -> T.Type
+replaceRigid (T.TFun t1 t2) = T.TFun (replaceRigid t1) (replaceRigid t2)
+replaceRigid T.TInt = T.TInt
+replaceRigid (T.TTup ts) = T.TTup (map (replaceRigid) ts)
+replaceRigid (T.TNamed n ts) = T.TNamed n (map replaceRigid ts)
+replaceRigid (T.TUnion ts) = T.TUnion (Set.map replaceRigid ts)
+replaceRigid (T.TyVar _ v) = T.TyVar T.Rigid v
+
 data UnifyContext = UnifyContext SourceRange T.Type T.Type
 
 unify :: SourceRange -> T.Type -> T.Type -> TM Subst
@@ -207,6 +215,10 @@ infer env expr = case expr of
     S.Annot sr subex ty -> do
         (theta1, subex') <- infer env subex
         ty' <- convertType (envAliases env) sr ty
+        -- Make sure the type of the subexpression matches the type with rigid
+        -- variables, then make it instantiable variables instead for the rest
+        -- of the code.
+        void $ unify sr (T.exprType subex') (replaceRigid ty')
         theta2 <- unify sr (T.exprType subex') ty'
         return (theta2 <> theta1, theta2 >>! subex')  -- TODO: quadratic complexity
 
diff --git a/typecheck/CC/Typecheck/Types.hs b/typecheck/CC/Typecheck/Types.hs
index 3f3c471..3009ca1 100644
--- a/typecheck/CC/Typecheck/Types.hs
+++ b/typecheck/CC/Typecheck/Types.hs
@@ -99,5 +99,4 @@ convertType' aliases extraVars sr origtype = do
     convert mp (S.TTup ts) = T.TTup (map (convert mp) ts)
     convert mp (S.TNamed n ts) = T.TNamed n (map (convert mp) ts)
     convert mp (S.TUnion ts) = T.TUnion (Set.map (convert mp) ts)
-    -- TODO: Should this be Rigid? I really don't know how this works.
-    convert mp (S.TyVar n) = T.TyVar T.Rigid (mp Map.! n)
+    convert mp (S.TyVar n) = T.TyVar T.Instantiable (mp Map.! n)
-- 
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