From 3a71d9c6c61afa3efb6bc190bf1ddae644ca0dff Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom@tomsmeding.com>
Date: Wed, 28 Aug 2024 23:28:57 +0200
Subject: WIP TH for non-base ASTs

---
 sharing-recovery.cabal |  3 +++
 test/Arith/NonBase.hs  | 45 +++++++++++++++++++++++++++++++++
 test/Main.hs           |  1 +
 test/NonBaseTH.hs      | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 117 insertions(+)
 create mode 100644 test/Arith/NonBase.hs
 create mode 100644 test/NonBaseTH.hs

diff --git a/sharing-recovery.cabal b/sharing-recovery.cabal
index 1a7228c..74cc7dc 100644
--- a/sharing-recovery.cabal
+++ b/sharing-recovery.cabal
@@ -26,9 +26,12 @@ test-suite test
   main-is: Main.hs
   other-modules:
     Arith
+    Arith.NonBase
+    NonBaseTH
   hs-source-dirs: test
   build-depends:
     sharing-recovery,
     base,
+    template-haskell,
   default-language: Haskell2010
   ghc-options: -Wall
diff --git a/test/Arith/NonBase.hs b/test/Arith/NonBase.hs
new file mode 100644
index 0000000..79c4428
--- /dev/null
+++ b/test/Arith/NonBase.hs
@@ -0,0 +1,45 @@
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE StandaloneKindSignatures #-}
+module Arith.NonBase where
+
+import Data.Kind
+import Data.Type.Equality
+
+-- import NonBaseTH
+
+
+data Typ t where
+  TInt :: Typ Int
+  TBool :: Typ Bool
+  TPair :: Typ a -> Typ b -> Typ (a, b)
+  TFun :: Typ a -> Typ b -> Typ (a -> b)
+deriving instance Show (Typ t)
+
+instance TestEquality Typ where
+  testEquality TInt TInt = Just Refl
+  testEquality TBool TBool = Just Refl
+  testEquality (TPair a b) (TPair a' b')
+    | Just Refl <- testEquality a a'
+    , Just Refl <- testEquality b b'
+    = Just Refl
+  testEquality (TFun a b) (TFun a' b')
+    | Just Refl <- testEquality a a'
+    , Just Refl <- testEquality b b'
+    = Just Refl
+  testEquality _ _ = Nothing
+
+data PrimOp a b where
+  POAddI :: PrimOp (Int, Int) Int
+  POMulI :: PrimOp (Int, Int) Int
+  POEqI :: PrimOp (Int, Int) Bool
+deriving instance Show (PrimOp a b)
+
+type Arith :: Type -> Type
+data Arith t where
+  A_Var :: Typ t -> String -> Arith t
+  A_Let :: String -> Typ a -> Arith a -> Arith b -> Arith b
+  A_Prim :: PrimOp a b -> Arith a -> Arith b
+  A_Pair :: Arith a -> Arith b -> Arith (a, b)
+  A_If :: Arith Bool -> Arith a -> Arith a -> Arith a
+  A_Mono :: Arith Bool -> Arith Bool
diff --git a/test/Main.hs b/test/Main.hs
index 1a8d8e1..5a4d335 100644
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -6,6 +6,7 @@
 module Main where
 
 import Data.Expr.SharingRecovery
+import Data.Expr.SharingRecovery.Internal
 
 import Arith
 
diff --git a/test/NonBaseTH.hs b/test/NonBaseTH.hs
new file mode 100644
index 0000000..712b680
--- /dev/null
+++ b/test/NonBaseTH.hs
@@ -0,0 +1,68 @@
+{-# LANGUAGE LambdaCase #-}
+module NonBaseTH where
+
+import Data.List (sort)
+import Language.Haskell.TH
+
+
+-- | Define a new GADT that is a base-functor-like version of a given existing
+-- GADT AST.
+--
+-- 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
+  -> Name  -- ^ Name of the GADT to process
+  -> [Name]  -- ^ Constructors to exclude (chiefly Var, Let, Lam)
+  -> Q [Dec]
+defineBaseAST basename astname excludes = 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 detectRec :: BangType -> Q (Maybe Type)
+      detectRec (_, field) = _
+
+  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
+        _
+
+  constrs' <- concat <$> traverse processConstr constrs
+  _
+
+checkRetty :: Name -> Name -> [TyVarBndr a] -> Type -> Q ()
+checkRetty astname consname vars retty = do
+  case splitApps retty of
+    (ConT name, args)
+      | name /= astname -> fail $ "Could not parse return type of constructor " ++ pprint consname
+      | null args -> fail "Expected GADT to have type parameters"
+
+      | Just varnames <- traverse (\case VarT varname -> Just varname ; _ -> Nothing) (init args)
+      , allDistinct varnames
+      , all (`elem` map bndrName vars) varnames ->
+          return ()
+
+      | otherwise -> fail $ "All type parameters but the last one must be uniform over all constructors. "
+                            ++ "(Return type of constructor " ++ pprint consname ++ ")"
+    _ -> fail $ "Could not parse return type of constructor " ++ pprint consname
+
+splitApps :: Type -> (Type, [Type])
+splitApps = flip go []
+  where go (AppT t arg) tl = go t (arg : tl)
+        go t tl = (t, tl)
+
+allDistinct :: Ord a => [a] -> Bool
+allDistinct l =
+  let sorted = sort l
+  in all (uncurry (/=)) (zip sorted (drop 1 sorted))
+
+bndrName :: TyVarBndr a -> Name
+bndrName (PlainTV n _) = n
+bndrName (KindedTV n _ _) = n
-- 
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