Transformers instances #226

robrix · 2019-09-28T20:23:13Z

This PR builds on #206 to offer Carrier instances for various monad transformers vended by transformers, allowing much greater integration between the two ecosystems.

Defines Carrier instances for various types in transformers.
Defines a Carrier instance for IO. (Fixes LiftC IO is inconvenient #258.)
Defines a Carrier instance for Identity.
Depends on Inject/Project find effects nested on the left #219.
Depends on Base instances #206.

…ce for ExceptT.

robrix

Ready for review.

robrix · 2019-10-09T04:36:59Z

src/Control/Carrier.hs

@@ -9,7 +9,7 @@ module Control.Carrier
 , send
 ) where

-import {-# SOURCE #-} Control.Carrier.Class
+import Control.Carrier.Class


I was running into some weird compilation errors, and it occurred to me that I’d put the .hs-boot files on the wrong edges. Putting them on the Control.Effect.* types allows me to limit the boot files to just the datatypes & instances needed to define the base & transformers instances.

robrix · 2019-10-09T04:38:18Z

src/Control/Carrier/Class.hs

+newtype RWSTF w s a = RWSTF { unRWSTF :: (a, s, w) }
+  deriving (Functor)
+
+toRWSTF :: Monoid w => w -> (a, s, w) -> RWSTF w s a
+toRWSTF w (a, s, w') = RWSTF (a, s, mappend w w')


This was a lot easier than trying to futz around with swapping triples. Also, did you know that there’s no Functor instance for (,,)? What a pain.

Jesus, yeah, I remember that. That shit sucks. Probably wanna INLINE this bad boy just to be sure, though.

robrix · 2019-10-09T04:38:52Z

src/Control/Carrier/Class.hs

+  eff (L (Throw e))     = Except.throwE e
+  eff (L (Catch m h k)) = Except.catchE m h >>= k


I’d been writing these all out long-form for a while when it hit me that I can do it so much more easily with the operations transformers exports.

This is remarkable to me for many reasons, but most notably because it’s a visceral display of fused-effects as an algebraic interface to mtl.

This is remarkable to me for many reasons, but most notably because it’s a visceral display of fused-effects as an algebraic interface to mtl.

…algebraic interface to transformers.

robrix · 2019-10-09T04:39:52Z

src/Control/Carrier/Class.hs

+instance (Carrier sig m, Effect sig, Monoid w) => Carrier (Reader r :+: Writer w :+: State s :+: sig) (RWS.CPS.RWST r w s m) where
+  eff (L (Ask       k))      = RWS.CPS.ask >>= k
+  eff (L (Local f m k))      = RWS.CPS.local f m >>= k
+  eff (R (L (Tell w k)))     = RWS.CPS.tell w *> k
+  eff (R (L (Listen m k)))   = RWS.CPS.listen m >>= uncurry (flip k)
+  eff (R (L (Censor f m k))) = RWS.CPS.censor f m >>= k
+  eff (R (R (L (Get   k))))  = RWS.CPS.get >>= k
+  eff (R (R (L (Put s k))))  = RWS.CPS.put s *> k
+  eff (R (R (R other)))      = RWS.CPS.rwsT $ \ r s -> unRWSTF <$> eff (handle (RWSTF ((), s, mempty)) (\ (RWSTF (x, s, w)) -> toRWSTF w <$> RWS.CPS.runRWST x r s) other)


My name is Ozymandias, King of Kings;
Look on my Works, ye Mighty, and despair!

I may never understand what RWS is for, but at least I know how to write a Carrier instance for it.

Bro, how have we never talked about this? I’ve run businesses atop RWS.

Okay maybe that’s a slight exaggeration. I have used RWS in production. It’s good. And we have an issue about this (#162) that this should address.

I would like to know more!

robrix · 2019-10-09T04:40:25Z

src/Control/Carrier/Error/Either.hs

-  eff (L (Throw e))     = ErrorC (ExceptT (pure (Left e)))
-  eff (L (Catch m h k)) = ErrorC (ExceptT (runError m >>= either (either (pure . Left) (runError . k) <=< runError . h) (runError . k)))
-  eff (R other)         = ErrorC (ExceptT (eff (handle (Right ()) (either (pure . Left) runError) other)))
+  eff = ErrorC . eff . handleCoercible


So, so happy with this.

robrix · 2019-10-09T04:44:39Z

src/Control/Effect/Choose.hs-boot

+newtype Choose m k
+  = Choose (Bool -> m k)
+
+instance HFunctor Choose


The .hs-boot files for the effects have to export the effect datatypes, but also the HFunctor instance, since that’s a superclass of Carrier. We don’t need the Effect or Functor instances, since they’re not involved in the base or transformers instances; and certainly not the Generic1 instances.

robrix · 2019-10-09T04:45:10Z

src/Control/Effect/Error.hs-boot

+data Error exc m k
+  = Throw exc
+  | forall b . Catch (m b) (exc -> m b) (b -> m k)
+
+instance HFunctor (Error exc)


This will get split up following #247, of course.

robrix · 2019-10-09T04:48:03Z

src/Control/Effect/NonDet.hs

-import Control.Effect.Choose hiding ((<|>), many, some, optional)
-import Control.Effect.Empty hiding (empty, guard)
+import Control.Effect.Choose (Choose(..))
+import Control.Effect.Empty (Empty(..))


Been meaning to do this for a while—it’s simpler to only list what we want to re-export.

robrix

Added a couple of valuable instances: Carrier (Lift IO) IO and Carrier Pure Identity.

robrix · 2019-10-11T03:10:23Z

src/Control/Carrier/Class.hs

+instance Carrier (Lift IO) IO where
+  eff = join . unLift


This is pretty obvious in hindsight; I expect it’ll obviate the need for the vast majority of runMs.

robrix · 2019-10-11T03:10:48Z

src/Control/Carrier/Class.hs

+instance Carrier Pure Identity where
+  eff v = case v of {}


transformers stacks tend to end with Identity or IO, so this seems pretty natural to support.

Any use of EmptyCase is a win.

patrickt · 2019-10-11T03:22:36Z

src/Control/Carrier/Class.hs

+newtype RWSTF w s a = RWSTF { unRWSTF :: (a, s, w) }
+  deriving (Functor)
+
+toRWSTF :: Monoid w => w -> (a, s, w) -> RWSTF w s a
+toRWSTF w (a, s, w') = RWSTF (a, s, mappend w w')


Jesus, yeah, I remember that. That shit sucks. Probably wanna INLINE this bad boy just to be sure, though.

patrickt · 2019-10-11T03:23:08Z

src/Control/Carrier/Class.hs

+instance (Carrier sig m, Effect sig, Monoid w) => Carrier (Reader r :+: Writer w :+: State s :+: sig) (RWS.CPS.RWST r w s m) where
+  eff (L (Ask       k))      = RWS.CPS.ask >>= k
+  eff (L (Local f m k))      = RWS.CPS.local f m >>= k
+  eff (R (L (Tell w k)))     = RWS.CPS.tell w *> k
+  eff (R (L (Listen m k)))   = RWS.CPS.listen m >>= uncurry (flip k)
+  eff (R (L (Censor f m k))) = RWS.CPS.censor f m >>= k
+  eff (R (R (L (Get   k))))  = RWS.CPS.get >>= k
+  eff (R (R (L (Put s k))))  = RWS.CPS.put s *> k
+  eff (R (R (R other)))      = RWS.CPS.rwsT $ \ r s -> unRWSTF <$> eff (handle (RWSTF ((), s, mempty)) (\ (RWSTF (x, s, w)) -> toRWSTF w <$> RWS.CPS.runRWST x r s) other)


Bro, how have we never talked about this? I’ve run businesses atop RWS.

patrickt · 2019-10-11T03:24:30Z

src/Control/Carrier/Class.hs

+instance (Carrier sig m, Effect sig, Monoid w) => Carrier (Reader r :+: Writer w :+: State s :+: sig) (RWS.CPS.RWST r w s m) where
+  eff (L (Ask       k))      = RWS.CPS.ask >>= k
+  eff (L (Local f m k))      = RWS.CPS.local f m >>= k
+  eff (R (L (Tell w k)))     = RWS.CPS.tell w *> k
+  eff (R (L (Listen m k)))   = RWS.CPS.listen m >>= uncurry (flip k)
+  eff (R (L (Censor f m k))) = RWS.CPS.censor f m >>= k
+  eff (R (R (L (Get   k))))  = RWS.CPS.get >>= k
+  eff (R (R (L (Put s k))))  = RWS.CPS.put s *> k
+  eff (R (R (R other)))      = RWS.CPS.rwsT $ \ r s -> unRWSTF <$> eff (handle (RWSTF ((), s, mempty)) (\ (RWSTF (x, s, w)) -> toRWSTF w <$> RWS.CPS.runRWST x r s) other)


Okay maybe that’s a slight exaggeration. I have used RWS in production. It’s good. And we have an issue about this (#162) that this should address.

patrickt · 2019-10-11T03:25:09Z

src/Control/Effect/Lift.hs

+Predefined carriers:
+
+* "Control.Carrier.Lift"
+* 'IO'


This is awesome.

Should we give an example somewhere of using runM versus discharging to IO directly?

Maybe, but I don’t think we need to hold up 1.0 for it.

patrickt · 2019-10-11T03:28:58Z

ChangeLog.md

@@ -14,6 +14,10 @@

 - Adds a `NonDetC` carrier for `NonDet` in `Control.Effect.NonDet.Maybe`. ([#227](https://github.com/fused-effects/fused-effects/pull/227))

+- Defines `Carrier` instances for a number of types in `base`, including `Either`, `Maybe`, `[]`, and `IO`. ([#206](https://github.com/fused-effects/fused-effects/pull/206))
+
+- Defines `Carrier` instances for a number of types in `transformers`. ([#226](https://github.com/fused-effects/fused-effects/pull/226))


We should probably add, like, a docs/carriers.md document detailing what the deal is with what Carrier people should use.

patrickt · 2019-10-11T03:30:40Z

src/Control/Carrier/Class.hs

+instance Carrier Pure Identity where
+  eff v = case v of {}


Any use of EmptyCase is a win.

patrickt · 2019-10-11T03:31:27Z

src/Control/Carrier/Class.hs

+  eff (L (Throw e))     = Except.throwE e
+  eff (L (Catch m h k)) = Except.catchE m h >>= k


This is remarkable to me for many reasons, but most notably because it’s a visceral display of fused-effects as an algebraic interface to mtl.

robrix · 2019-10-11T14:04:04Z

Ughhhh the CPS Writer & RWS transformers require 8.6+ 😭

These are unavailable prior to ghc 8.6, and I’d rather these instances than ghc 8.2 & 8.4 or have to use CPP.

robrix added 24 commits September 28, 2019 16:15

Define a Carrier instance for ReaderT.

c6e4fc0

Rename the import of ReaderT.

4d7b3a3

Define a Carrier instance for strict StateT.

2126ffd

Define a Carrier instance for lazy StateT.

d1bab5e

Merge branch 'base-instances' into transformers-instances

74bd9cc

Merge branch 'base-instances' into transformers-instances

b016860

Merge branch 'master' into transformers-instances

182e2b1

Define a Carrier instance for ExceptT.

3e7b48c

Define the Carrier instance for ErrorC in terms of the Carrier instan…

5957d6e

…ce for ExceptT.

Use .hs-boot files for the effects only.

22d64a1

Define a Carrier instance for Writer.CPS.

bba5f08

Simplify the Carrier instance for ReaderT.

f36ddba

Simplify the Carrier instance for Lazy.StateT.

1807850

Simplify the Carrier instance for Strict.StateT.

e233448

Simplify the Carrier instance for ExceptT.

40151fa

Alphabetize.

a60fc93

Define a Carrier instance for Writer.Lazy.

a640050

Define a Carrier instance for Writer.Strict.

0d51a1e

Define a Carrier instance for RWS.CPS.

2019c01

Define a Carrier instance for RWS.Lazy.

4d7c92a

Define a Carrier instance for RWS.Strict.

a3dbffa

Add a heading for the base instances.

550c236

Add a changelog entry for #206.

062f356

Add a changelog entry for the transformers instances.

9be6954

robrix changed the base branch from base-instances to master October 9, 2019 04:35

robrix added 4 commits October 9, 2019 00:43

🔥 the redundant instances from the cycle breakers.

48af21e

Derive these the old-fashioned way.

bfbebea

Rejigger the imports for the NonDet modules.

1dc0420

Don’t re-export the types.

f142b86

robrix commented Oct 9, 2019

View reviewed changes

robrix marked this pull request as ready for review October 9, 2019 04:48

robrix added 6 commits October 10, 2019 22:57

Merge branch 'master' into transformers-instances

6043a51

Define a Carrier instance for Identity.

5ef6e34

Define a Carrier instance for IO.

0b17a4b

📝 the Lift carriers.

b865ddb

Document the fact of the Carrier instance for Identity.

b4d5d67

Note some of the new Carrier instances.

5dc3add

robrix commented Oct 11, 2019

View reviewed changes

patrickt reviewed Oct 11, 2019

View reviewed changes

robrix added 4 commits October 11, 2019 17:47

Inline toRWSTF.

1c395bc

🔥 the CPS instances.

6f9fc2e

These are unavailable prior to ghc 8.6, and I’d rather these instances than ghc 8.2 & 8.4 or have to use CPP.

Merge branch 'master' into transformers-instances

327895e

🔥 some redundant imports.

85d5388

robrix merged commit 4abe611 into master Oct 11, 2019

robrix deleted the transformers-instances branch October 11, 2019 22:09

This was referenced Oct 15, 2019

Effect laws #239

Merged

Rename Carrier to Algebra. #285

Merged

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Transformers instances #226

Transformers instances #226

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robrix commented Oct 11, 2019

		eff (L (Throw e)) = Except.throwE e
		eff (L (Catch m h k)) = Except.catchE m h >>= k

Transformers instances #226

Transformers instances #226

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robrix commented Oct 11, 2019

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