polysemy VS ghc

Thirdly, composing arbitrary effects without losing state is really, really difficult. Things are fine when you limit yourself to State and Reader, sure, but once you start with nondeterminism you’ll discover it’s shockingly easy to produce behaviors that are baffling unless you’ve spent a preposterous amount of time thinking about this stuff. (I’ve been bitten in prod by silent state-dropping bugs, and rarely have I been more flummoxed.) Consider this example, which produces silent changes in the semantics of <|> depending on whether you use it inside or outside of a higher-order effect. Every single effect library (besides the still-unreleased eff) gets certain combinations of effects + nondeterminism wrong. You could make the argument that most people don’t use nondeterministic monads, but eDSLs really shine when you have access to them, as you can turn a concrete interpreter to an abstract one fairly easily.

Looking for a few projects that make use of it, I found accelerate, hawk, polysemy and pretty-simple, so I'll be interested to poke around in their code and see how they have things set up.

Right, I think I'll just give it a shot to see. Polysemy is nice but I'm still having trouble getting what I want out of it (which may very well be entirely a fault of my own understanding)

Languages such as Koka only support algebraic effects, not scoping operations such as catch and listen. The Effect Handlers in Scope paper introduces scoping operations, which lead to the Haskell libraries fused-effects and polysemy, but they turned out to have some weird semantics. eff is her effort to fix that.

*But I'm not terribly well versed in Scala's other DI offerings. I came from Haskell and didn't find anything in Scala that clicked with me until I found ZIO. It reminded me a lot of my favorite way of writing Haskell programs (https://github.com/polysemy-research/polysemy)—albeit with a completely different implementation.

Depending on who you ask, a programming language can be different things. If you ask the Haskell community, many will tell you that the language is the Haskell specification, and that what currently is being used is not Haskell itself, but an extension of Haskell that is supported by the GHC compiler. Similar to the C language, a programming language would be a specification.

bss@monster % cat > File.hs pred 1 = 4 succ 4 = 1 succ 1 = 2 bss@monster % ghci -XNoImplicitPrelude File.hs GHCi, version 9.0.2: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/bss/.ghc/ghci.conf [1 of 1] Compiling Main ( File.hs, interpreted ) Ok, one module loaded. (0.04 secs,) GHCi> pred 1 4 it :: GHC.Num.Num p => p (0.01 secs, 79,688 bytes) GHCi> succ 1 2 it :: GHC.Num.Num p => p (0.01 secs, 78,088 bytes)

GHCi, version 9.0.2: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/bss/.ghc/ghci.conf GHCi> :{ GHCi| pred 1 = 4 GHCi| succ 4 = 1 GHCi| succ 1 = 2 GHCi| :} pred :: (Eq a, Num a, Num p) => a -> p succ :: (Eq a, Num a, Num p) => a -> p (0.04 secs, 0 bytes) GHCi> pred 1 4 it :: Num p => p (0.01 secs, 62,784 bytes) GHCi> succ 4 1 it :: Num p => p (0.01 secs, 61,864 bytes) GHCi> succ 1 2 it :: Num p => p (0.01 secs, 61,928 bytes)

[jumper deriving-trans @master]$ nix develop [jumper deriving-trans @master]$ cabal repl Build profile: -w ghc-9.2.4 -O1 In order, the following will be built (use -v for more details): - deriving-trans-0.8.0.0 (lib) (first run) Preprocessing library for deriving-trans-0.8.0.0.. GHCi, version 9.2.4: https://www.haskell.org/ghc/ :? for help :1:1: warning: [-Wmissing-local-signatures] Polymorphic local binding with no type signature: _compileParsedExpr :: forall {a}. ghc-prim:GHC.Types.IO a -> ghc-prim:GHC.Types.IO a macro 'doc' overwrites builtin command. Use ':def!' to overwrite. Loaded GHCi configuration from /home/jumper/.ghc/ghci.conf : warning: [-Wunused-packages] The following packages were specified via -package or -package-id flags, but were not needed for compilation: - unliftio-core-0.2.0.1-4aEaNp8xHRK6Ey6KEoq0BU - transformers-base-0.4.6-BO3yqj8kK7N1FV1bV9s5yP - transformers-0.6.0.4-F8uVRiS1g8K3h8Rsxr0UMd - resourcet-1.2.6-GkviYKmTWlu24k3qS4ih9J - random-1.2.1.1-DsRhotp5Bx34wv1CRGomTB - primitive-0.7.3.0-1lmZ3PZm6JAE7HP2AgnD1I - mtl-2.3.1-A9dQ96c1wA8f1tgidK0Kj - monad-control-identity-0.2.0.0-C96eAiqAq5HPusYxrNzzr - monad-control-1.0.3.1-9k4XD0NyvERHbSFKJZxIuC - logict-0.8.0.0-5sZNS401Hrq2OkYkpVhzEI - exceptions-0.10.7-LidfE6miSbs6Y1NYj1lBV5 - base-4.16.3.0 [1 of 7] Compiling Control.Monad.Accum.OrphanInstances ( src/Control/Monad/Accum/OrphanInstances.hs, interpreted ) [2 of 7] Compiling Control.Monad.Select.OrphanInstances ( src/Control/Monad/Select/OrphanInstances.hs, interpreted ) [3 of 7] Compiling Control.Monad.Trans.Elevator ( src/Control/Monad/Trans/Elevator.hs, interpreted ) [4 of 7] Compiling Control.Monad.Trans.Compose.Transparent ( src/Control/Monad/Trans/Compose/Transparent.hs, interpreted ) [5 of 7] Compiling Control.Monad.Trans.Compose ( src/Control/Monad/Trans/Compose.hs, interpreted ) [6 of 7] Compiling Control.Monad.Trans.Compose.Stack ( src/Control/Monad/Trans/Compose/Stack.hs, interpreted ) [7 of 7] Compiling Control.Monad.Trans.Compose.Infix ( src/Control/Monad/Trans/Compose/Infix.hs, interpreted ) Ok, 7 modules loaded. λ *Control.Monad.Trans.Compose > :set -XPartialTypeSignatures λ *Control.Monad.Trans.Compose > import Control.Monad.Trans.Compose.Infix λ *Control.Monad.Trans.Compose Control.Monad.Trans.Compose.Infix > import Control.Monad.Trans.Compose.Transparent λ *Control.Monad.Trans.Compose Control.Monad.Trans.Compose.Infix Control.Monad.Trans.Compose.Transparent > runTransparentT ./> (`Mtl.T.runReaderT` 'a') ./> (`Mtl.T.runReaderT` True) $ (,) <$> (Mtl.ask :: _ Char) <*> (Mtl.ask :: _ Bool) :4:98: warning: [-Wpartial-type-signatures] • Found type wildcard ‘_’ standing for ‘ComposeT (Mtl.T.ReaderT Bool) (ComposeT (Mtl.T.ReaderT Char) (Elevator NoT)) IO :: * -> *’ • In the type ‘_ Char’ In an expression type signature: _ Char In the second argument of ‘(<$>)’, namely ‘(Mtl.ask :: _ Char)’ :4:98: warning: [-Wmonomorphism-restriction] • The Monomorphism Restriction applies to the binding for ‘’ Consider giving it a type signature • In the second argument of ‘(<$>)’, namely ‘(Mtl.ask :: _ Char)’ In the first argument of ‘(<*>)’, namely ‘(,) <$> (Mtl.ask :: _ Char)’ In the second argument of ‘($)’, namely ‘(,) <$> (Mtl.ask :: _ Char) <*> (Mtl.ask :: _ Bool)’ :4:122: warning: [-Wpartial-type-signatures] • Found type wildcard ‘_’ standing for ‘ComposeT (Mtl.T.ReaderT Bool) (ComposeT (Mtl.T.ReaderT Char) (Elevator NoT)) IO :: * -> *’ • In the type ‘_ Bool’ In an expression type signature: _ Bool In the second argument of ‘(<*>)’, namely ‘(Mtl.ask :: _ Bool)’ :4:122: warning: [-Wmonomorphism-restriction] • The Monomorphism Restriction applies to the binding for ‘’ Consider giving it a type signature • In the second argument of ‘(<*>)’, namely ‘(Mtl.ask :: _ Bool)’ In the second argument of ‘($)’, namely ‘(,) <$> (Mtl.ask :: _ Char) <*> (Mtl.ask :: _ Bool)’ In the first argument of ‘GHC.GHCi.ghciStepIO :: IO a -> IO a’, namely ‘(runTransparentT ./> (`Mtl.T.runReaderT` 'a') ./> (`Mtl.T.runReaderT` True) $ (,) <$> (Mtl.ask :: _ Char) <*> (Mtl.ask :: _ Bool))’ ('a',True)

GHCi, version 8.10.7: https://www.haskell.org/ghc/ :? for help

Haskell (in the form of GHC) uses Alex, which is regular expression-based.

A good starting point for the JS backend is the module-level documentation in GHC.StgToJS, but it doesn't look like there's much good documentation yet, no.

GHCi, version 9.4.2: https://www.haskell.org/ghc/ :? for help ghci> :load Evolution.hs [1 of 2] Compiling Main ( Evolution.hs, interpreted ) Ok, one module loaded. ghci> :t fac four fac four :: Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ (Succ Zero)))))))))))))))))))))))