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An effect permitting unfold ???
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| import Control.Lens.Cons (Cons (..), cons, (<|)) | |
| import Data.Maybe (maybe) | |
| import Data.Monoid (Monoid) | |
| unfoldM :: (Cons s s a a, Monoid s, Monad m) => (b -> m (Maybe (a,b))) -> b -> m s | |
| unfoldM f b = maybe (return mempty) (\(a,b') -> cons a <$> unfoldM f b') =<< f b |
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