1 files changed, 54 insertions, 14 deletions

diff --git a/test/NonBaseTH.hs b/test/NonBaseTH.hs
index 712b680..f3c34f3 100644
--- a/test/NonBaseTH.hs
+++ b/test/NonBaseTH.hs
@@ -1,7 +1,11 @@
 {-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE TemplateHaskellQuotes #-}
 module NonBaseTH where
 
-import Data.List (sort)
+import Control.Monad (when)
+import Data.List (sort, foldl', tails)
+import Data.Maybe (fromMaybe)
 import Language.Haskell.TH
 
 
@@ -11,34 +15,65 @@ import Language.Haskell.TH
 -- Remember to use 'lookupTypeName' or 'lookupValueName' instead of normal
 -- quotes in case of punning of data types and constructors.
 defineBaseAST
-  :: Name  -- ^ Name of the (base-functor-like) data type to define
+  :: String  -- ^ Name of the (base-functor-like) data type to define
   -> Name  -- ^ Name of the GADT to process
-  -> [Name]  -- ^ Constructors to exclude (chiefly Var, Let, Lam)
+  -> [Name]  -- ^ Constructors to exclude (Var and Let, plus any other scoping construct)
+  -> (String -> String)  -- ^ Constructor renaming function
   -> Q [Dec]
-defineBaseAST basename astname excludes = do
+defineBaseAST basename astname excludes renameConstr = do
   info <- reify astname
   (params, constrs) <- case info of
     TyConI (DataD [] _ params Nothing constrs _) -> return (params, constrs)
     _ -> fail $ "Unsupported datatype: " ++ pprint astname
 
-  let recvar = mkName "r"
+  let basename' = mkName basename
+      recvar = mkName "r"
 
-  let detectRec :: BangType -> Q (Maybe Type)
-      detectRec (_, field) = _
+  let detectRec :: Type -> Q (Maybe Type)
+      detectRec field = do
+        let (core, args) = splitApps field
+        case core of
+          ConT n
+            | n == astname -> return (Just (VarT recvar `AppT` last args))
+          ListT
+            | [arg] <- args -> fmap (ListT `AppT`) <$> detectRec arg
+          TupleT k
+            | length args == k -> fmap (foldl' AppT (TupleT k)) . sequence <$> traverse detectRec args
+          _ -> do
+            when (pprint astname `infixOf` pprint field) $
+              reportWarning $ "Field\n  " ++ pprint field ++ "\nseems to refer to "
+                              ++ pprint astname ++ " in unsupported ways; ignoring those occurrences."
+            return Nothing
 
   let processConstr con = do
         (vars, ctx, names, fields, retty) <- case con of
           ForallC vars ctx (GadtC names fields retty) -> return (vars, ctx, names, fields, retty)
           GadtC names fields retty -> return ([], [], names, fields, retty)
           _ -> fail "Unsupported constructors found"
-        checkRetty astname (head names) vars retty
-        _
+        case filter (`notElem` excludes) names of
+          [] -> return []
+          names' -> do
+            let names'' = map (mkName . renameConstr . nameBase) names'
+            retty' <- fixRetty basename' astname (head names) recvar vars retty
+            fields' <- traverse (\(ba, t) -> (ba,) . fromMaybe t <$> detectRec t) fields
+            return [ForallC (map cleanupBndr vars ++ [PlainTV recvar SpecifiedSpec]) ctx (GadtC names'' fields' retty')]
 
+  let params' = map cleanupBndr (init params ++ [PlainTV recvar (), last params])
   constrs' <- concat <$> traverse processConstr constrs
-  _
+  return [DataD [] (mkName basename) params' Nothing constrs' []]
 
-checkRetty :: Name -> Name -> [TyVarBndr a] -> Type -> Q ()
-checkRetty astname consname vars retty = do
+-- | Remove `:: Type` annotations because they unnecessarily require the user
+-- to enable KindSignatures. Any other annotations we leave, in case the user
+-- wrote them and they are necessary.
+cleanupBndr :: TyVarBndr a -> TyVarBndr a
+cleanupBndr (KindedTV name x k) | isType k = PlainTV name x
+  where isType StarT = True
+        isType (ConT n) | n == ''Type = True
+        isType _ = False
+cleanupBndr b = b
+
+fixRetty :: Name -> Name -> Name -> Name -> [TyVarBndr a] -> Type -> Q Type
+fixRetty basename astname consname recvar vars retty = do
   case splitApps retty of
     (ConT name, args)
       | name /= astname -> fail $ "Could not parse return type of constructor " ++ pprint consname
@@ -47,7 +82,7 @@ checkRetty astname consname vars retty = do
       | Just varnames <- traverse (\case VarT varname -> Just varname ; _ -> Nothing) (init args)
       , allDistinct varnames
       , all (`elem` map bndrName vars) varnames ->
-          return ()
+          return (foldl' AppT (ConT basename) (init args ++ [VarT recvar, last args]))
 
       | otherwise -> fail $ "All type parameters but the last one must be uniform over all constructors. "
                             ++ "(Return type of constructor " ++ pprint consname ++ ")"
@@ -55,7 +90,8 @@ checkRetty astname consname vars retty = do
 
 splitApps :: Type -> (Type, [Type])
 splitApps = flip go []
-  where go (AppT t arg) tl = go t (arg : tl)
+  where go (ParensT t) tl = go t tl
+        go (AppT t arg) tl = go t (arg : tl)
         go t tl = (t, tl)
 
 allDistinct :: Ord a => [a] -> Bool
@@ -66,3 +102,7 @@ allDistinct l =
 bndrName :: TyVarBndr a -> Name
 bndrName (PlainTV n _) = n
 bndrName (KindedTV n _ _) = n
+
+infixOf :: Eq a => [a] -> [a] -> Bool
+short `infixOf` long = any (`startsWith` short) (tails long)
+  where a `startsWith` b = take (length b) a == b