Monoid instance for FreeT #8
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| @@ -76,6 +79,18 @@ instance monadRecFreeT :: (Functor f, Monad m) => MonadRec (FreeT f m) where | |||
| Loop s1 -> go s1 | |||
| Done a -> pure a | |||
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| instance semigroupFreeT :: (Functor f, Monad m, Monoid w) => Semigroup (FreeT f m w) where | |||
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You can relax the Monad constraint to Applicative and use append = lift2 append.
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Although the lift2 change has been made you still have Monad m here 😄
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Also, this probably only needs Semigroup w now?
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Oh jeez >< I didn't even see that, thank you. The Haskell has run deep
| y' <- y | ||
| pure (x' <> y') | ||
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| instance monoidFreeT :: (Functor f, Monad m, Monoid w) => Monoid (FreeT f m w) where |
| instance monoidFreeT :: (Functor f, Monad m, Monoid w) => Monoid (FreeT f m w) where | ||
| mempty = pure mempty | ||
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| -- instance monadEffFreeT :: (Functor f, MonadEff m) => MonadEff (FreeT f m) where |
| import Control.Monad.Rec.Class (class MonadRec, Step(..), tailRecM) | ||
| import Control.Monad.Trans.Class (class MonadTrans) | ||
| import Control.Monad.Trans.Class (class MonadTrans, lift) |
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Sorry, I didn't see this until now. I think it should be minimal now, sorry about that commented instance. |
| @@ -76,6 +79,18 @@ instance monadRecFreeT :: (Functor f, Monad m) => MonadRec (FreeT f m) where | |||
| Loop s1 -> go s1 | |||
| Done a -> pure a | |||
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| instance semigroupFreeT :: (Functor f, Monad m, Monoid w) => Semigroup (FreeT f m w) where | |||
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Although the lift2 change has been made you still have Monad m here 😄
| append = lift2 append | ||
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| instance monoidFreeT :: (Functor f, Monad m, Monoid w) => Monoid (FreeT f m w) where | ||
| mempty = pure mempty |
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Likewise you only need Applicative m here.
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Actually I'm not sure about that - FreeT's Apply instance depends on Monad due to the use of ap - I'm not sure if there's a way around that, I'm not too familiar with FreeT's design :x
| @@ -19,6 +19,7 @@ | |||
| "purescript-control": "^2.0.0", | |||
| "purescript-tailrec": "^2.0.0", | |||
| "purescript-transformers": "^2.0.1", | |||
| "purescript-exists": "^2.0.0" | |||
| "purescript-exists": "^2.0.0", | |||
| "purescript-eff": "^2.0.0" | |||
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You can drop this dependency now, as there's no Eff instance.
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"The import of module Data.Semigroup is redundant" |
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Sorry, still learning how to use the toolchain >< |
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This is a pretty terrible pull request, but I still think the idea is valid.
It wouldn't be wise to write this instance for every monad, Haskell gets away with it by cherrypicking instances - they have one for
IOandMaybefor instance, but that's about it. Also, this would conflate with the meaning behind the monadic instance for lists[], so I think it's wise to stay away from that level of generality.However, this instance for FreeT (and nest, Eff and Aff) could be useful. In my case, I'm using them to "merge" some
PerformActionroutines in Thermite:T.simpleSpec (performAction1 <> performAction2 <> ...) renderThe monoid instance for
Specshould also be capable of using this behavior in FreeT (and CoTransformer).