From fce54e789996970dfe1bd71914f0c6f6669415a0 Mon Sep 17 00:00:00 2001
From: sebastianselander <sebastian.selander@gmail.com>
Date: Mon, 6 Mar 2023 16:41:59 +0100
Subject: [PATCH] documented possible bad functions

---
 sample-programs/basic-5        | 13 ++-----------
 src/TypeChecker/TypeChecker.hs | 26 +++++++++++++++-----------
 2 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/sample-programs/basic-5 b/sample-programs/basic-5
index 7175091..9a9a723 100644
--- a/sample-programs/basic-5
+++ b/sample-programs/basic-5
@@ -1,17 +1,8 @@
 -- double : _Int -> _Int ;
 -- double n = n + n;
 
-apply : ('a -> 'b -> 'c) -> 'a -> 'b -> 'c ;
-apply f x y = f x y ;
-
 id : 'a -> 'a ;
 id x = x ;
 
-add : _Int -> _Int -> _Int ;
-add x y = x + y ;
-
-main : _Int -> _Int -> _Int ;
-main = apply (id add) ;
-
-idadd : _Int -> _Int -> _Int ;
-idadd = id add ;
+main : ('a -> 'b -> 'c) ;
+main = id ;
diff --git a/src/TypeChecker/TypeChecker.hs b/src/TypeChecker/TypeChecker.hs
index b99313d..af4734d 100644
--- a/src/TypeChecker/TypeChecker.hs
+++ b/src/TypeChecker/TypeChecker.hs
@@ -45,6 +45,7 @@ typecheck = run . checkPrg
 
 {- | Start by freshening the type variable of data types to avoid clash with
 other user defined polymorphic types
+This might be wrong for type constructors that work over several variables
 -}
 freshenData :: Data -> Infer Data
 freshenData (Data (Constr name ts) constrs) = do
@@ -59,18 +60,21 @@ freshenData (Data (Constr name ts) constrs) = do
     let new_ts = map (freshenType fr') ts
     let new_constrs = map (freshenConstr fr') constrs
     return $ Data (Constr name new_ts) new_constrs
-  where
-    freshenType :: Ident -> Type -> Type
-    freshenType iden = \case
-        (TPol _) -> TPol iden
-        (TArr a b) -> TArr (freshenType iden a) (freshenType iden b)
-        (TConstr (Constr a ts)) ->
-            TConstr (Constr a (map (freshenType iden) ts))
-        rest -> rest
 
-    freshenConstr :: Ident -> Constructor -> Constructor
-    freshenConstr iden (Constructor name t) =
-        Constructor name (freshenType iden t)
+{- | Freshen all polymorphic variables, regardless of name
+| freshenType "d" (a -> b -> c) becomes (d -> d -> d)
+-}
+freshenType :: Ident -> Type -> Type
+freshenType iden = \case
+    (TPol _) -> TPol iden
+    (TArr a b) -> TArr (freshenType iden a) (freshenType iden b)
+    (TConstr (Constr a ts)) ->
+        TConstr (Constr a (map (freshenType iden) ts))
+    rest -> rest
+
+freshenConstr :: Ident -> Constructor -> Constructor
+freshenConstr iden (Constructor name t) =
+    Constructor name (freshenType iden t)
 
 checkData :: Data -> Infer ()
 checkData d = do