On Tue, Sep 27, 2022 at 10:15:29AM +1000, Isaac Elliott wrote:
https://pursuit.purescript.org/packages/purescript-tailrec/6.1.0/docs/Contro... seems like a good starting point
Seems like that package may have missed a trick to encode tail recursiveness through a distribution property: {-# LANGUAGE LambdaCase #-} {-# LANGUAGE DeriveFunctor #-} module RecExperiment where data Step a b = Loop a | Done b deriving Functor tailRec :: (a -> Step a b) -> a -> b tailRec f = go . f where go (Loop a) = go (f a) go (Done b) = b -- | This works for all monads tailRecM1 :: Monad m => (a -> m (Step a b)) -> a -> m b tailRecM1 f a = do f a >>= \case Loop a' -> tailRecM1 f a' Done b -> pure b -- | This works for all monads with a "distribute" operation over -- @Step a@ and is guaranteed tail recursive via @tailRec@. tailRecM2 :: Monad m => (m (Step a b) -> Step a (m b)) -> (a -> m (Step a b)) -> a -> m b tailRecM2 distribute f = tailRec (distribute . f)