Add experimental MonadRec instance for SFKT

spago.dhall

@@ -12,7 +12,14 @@ to generate this file without the comments in this block.
 -}
 { name = "logict"
 , dependencies =
-  [ "control", "lists", "maybe", "prelude", "transformers", "tuples" ]
+  [ "control"
+  , "lists"
+  , "maybe"
+  , "prelude"
+  , "tailrec"
+  , "transformers"
+  , "tuples"
+  ]
 , packages = ./packages.dhall
 , sources = [ "src/**/*.purs", "test/**/*.purs" ]
 }

src/Control/Monad/Logic/Trans.purs

@@ -8,6 +8,7 @@ import Control.MonadPlus (class MonadPlus, class Alternative, class Alt, class P
 import Control.Monad.Reader.Class (class MonadReader, local, class MonadAsk, ask)
 import Control.Monad.State.Class (class MonadState, state)
 import Control.Monad.Trans.Class (class MonadTrans, lift)
+import Control.Monad.Rec.Class (class MonadRec, Step(..))
 import Data.Functor (map)
 import Data.Tuple.Nested ((/\))
 import Data.List (List(Nil), (:))
@@ -78,3 +79,17 @@ instance MonadState s m => MonadState s (SFKT m) where
 
 instance Lazy (SFKT m a) where
     defer f = SFKT (\sk fk -> unSFKT (f unit) sk fk)
+
+instance Monad m => MonadRec (SFKT m) where
+    tailRecM :: forall acc b. (acc -> SFKT m (Step acc b)) -> acc -> SFKT m b
+    tailRecM f a0 = SFKT \sk fk -> go {sk: sk, fk: fk} a0
+        where
+            go :: forall ans. { sk :: SK (m ans) b, fk :: FK (m ans) } -> acc -> m ans
+            go r@{sk,fk} an =
+                let
+                    (SFKT sfktf) = f an
+                    success st fk' =
+                        case st of
+                            Loop an' -> go r an'
+                            Done b -> sk b fk'
+                 in sfktf success fk