From 540fcf9920df93452f66c22b978cd9f297a0279f Mon Sep 17 00:00:00 2001
From: Brent Yorgey <byorgey@gmail.com>
Date: Sat, 15 Jun 2024 23:48:57 -0500
Subject: [PATCH] bug fix: free vars in scope of tydef were being ignored; add
 minimal test case

---
 src/swarm-lang/Swarm/Language/Syntax/Util.hs | 2 +-
 test/unit/TestEval.hs                        | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/swarm-lang/Swarm/Language/Syntax/Util.hs b/src/swarm-lang/Swarm/Language/Syntax/Util.hs
index 9b839b2a12..16c303481c 100644
--- a/src/swarm-lang/Swarm/Language/Syntax/Util.hs
+++ b/src/swarm-lang/Swarm/Language/Syntax/Util.hs
@@ -128,7 +128,6 @@ freeVarsS f = go S.empty
     TRef {} -> pure s
     TRequireDevice {} -> pure s
     TRequire {} -> pure s
-    STydef {} -> pure s
     SRequirements x s1 -> rewrap $ SRequirements x <$> go bound s1
     TVar x
       | x `S.member` bound -> pure s
@@ -138,6 +137,7 @@ freeVarsS f = go S.empty
     SLet ls r x xty xreq s1 s2 ->
       let bound' = S.insert (lvVar x) bound
        in rewrap $ SLet ls r x xty xreq <$> go bound' s1 <*> go bound' s2
+    STydef x xdef tdInfo t1 -> rewrap $ STydef x xdef tdInfo <$> go bound t1
     SPair s1 s2 -> rewrap $ SPair <$> go bound s1 <*> go bound s2
     SBind mx mty mpty mreq s1 s2 -> rewrap $ SBind mx mty mpty mreq <$> go bound s1 <*> go (maybe id (S.insert . lvVar) mx bound) s2
     SDelay m s1 -> rewrap $ SDelay m <$> go bound s1
diff --git a/test/unit/TestEval.hs b/test/unit/TestEval.hs
index 265e62b56e..09f6affacc 100644
--- a/test/unit/TestEval.hs
+++ b/test/unit/TestEval.hs
@@ -339,6 +339,9 @@ testEval g =
                 `evaluatesTo` VInt 5
             )
         ]
+    , testCase
+        "tydef does not prevent forcing of recursive variables"
+        ("def forever = \\c. c; forever c end; tydef X = Int end; def go = forever move end" `evaluatesTo` VUnit)
     ]
  where
   tquote :: String -> Text