Add falsify to ghc-tests.cabal

tests/ghc-tests/ghc-tests.cabal

@@ -53,8 +53,9 @@ test-suite ghc-tests
        bytestring,
        time,
        deepseq,
-
+       falsify,
        mtl
+       
     main-is:          Main.hs
     other-modules: Chan001
                  , MVar001

tests/ghc-tests/tests/PBT/Expr.hs

+{-# LANGUAGE GADTs #-}
+
+module PBT.Expr where
+
+import Data.Text (Text)
+import Test.Falsify
+
+data Id a where
+  F :: Text -> Id (a -> b)
+  V :: Text -> Id a
+
+data Binder a where
+  Wild :: Id a -> Binder a
+
+data Expr a where
+  Var :: Id a -> Expr a
+  Lit :: a -> Expr a
+  App :: Expr (a -> b) -> Expr a -> Expr b
+  Lam :: Binder a -> Expr b -> Expr (a -> b)
+