Refactor to use continuation monad

exe/GarnetRs/Wrapped.hs

@@ -11,7 +11,10 @@ module GarnetRs.Wrapped (
     sumTree,
 ) where
 
+import Control.Monad.Cont
+import Control.Monad.Trans
 import Data.ByteString
+import Data.Function
 import Data.Word
 import Foreign
 import Foreign.C
@@ -38,20 +41,17 @@ data BTree a
     = Leaf a
     | Fork (BTree a) (BTree a)
 withBTree :: BTree Int64 -> (Raw.BTreeC -> IO a) -> IO a
-withBTree = flip \f -> \case
-    Leaf v ->
-        f $ Raw.BTreeC Raw.Leaf $ Raw.set_bTreeC_body_leaf $ Raw.Leaf_Body v
-    Fork l r ->
-        withBTree l \lRaw ->
-            withBTree r \rRaw ->
-                alloca \lPtr ->
-                    alloca \rPtr -> do
-                        poke lPtr lRaw
-                        poke rPtr rRaw
-                        f
-                            . Raw.BTreeC Raw.Fork
-                            . Raw.set_bTreeC_body_fork
-                            $ Raw.Fork_Body (unsafeFromPtr lPtr) (unsafeFromPtr rPtr)
+withBTree =
+    runContT . fix \f -> \case
+        Leaf v -> pure $ Raw.BTreeC Raw.Leaf $ Raw.set_bTreeC_body_leaf $ Raw.Leaf_Body v
+        Fork l r -> do
+            lRaw <- f l
+            rRaw <- f r
+            lPtr <- ContT alloca
+            rPtr <- ContT alloca
+            lift $ poke lPtr lRaw >> poke rPtr rRaw
+            pure . Raw.BTreeC Raw.Fork . Raw.set_bTreeC_body_fork $
+                Raw.Fork_Body (unsafeFromPtr lPtr) (unsafeFromPtr rPtr)
 
 hello :: ByteString -> IO ()
 hello s = useAsCString s $ Raw.hello . unsafeFromPtr

garnet.cabal

@@ -53,3 +53,4 @@ executable garnet
         bytestring,
         garnet-generated,
         hs-bindgen-runtime,
+        mtl,