feat(third_party/bazel): Check in rules_haskell from Tweag

third_party/bazel/rules_haskell/tests/haskell_doctest/Foo.hs

@@ -0,0 +1,14 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+
+module Foo (foo) where
+
+import Foreign.C.Types (CInt(..))
+
+foreign import ccall "c_add_one"
+  c_add_one :: CInt -> CInt
+
+-- |
+-- >>> foo
+-- 5
+foo :: Int
+foo = fromIntegral (c_add_one 4)