August 2022 - Haskell-Cafe

[ANN] plutus-simple-model-0.3 - minimal library to test Plutus/Cardano applications
by Anton Kholomiov 05 Aug '22

05 Aug '22

I’m happy to announce the release of a new version for plutus-simple-model <https://github.com/mlabs-haskell/plutus-simple-model>. It’s a minimal library to write test for Plutus/Cardano applications. It’s easy to use and blazing fast. We use it extensively in Mlabs City to test our Plutus applications. The new release is focused on those main features: - Reduce dependency set to make it as lean as possible. It depends only on plutus and cardano-ledger. - Support for Babbage era (use new features available in Vasil) - Support for Plutus V2 features (inlined datums, reference inputs, reference scripts, forward to redeemer, etc) - Write tutorial <https://mlabs-haskell.github.io/plutus-simple-model/> and update Hackage docs The main thing is Plutus V2 support. Also with cutdown on the list of dependencies it becomes much easier to update and use. I have removed big deps like plutus-apps, ouroboros and cardano-node. With this rewrite also it became 10 times faster. Links: github repo: https://github.com/mlabs-haskell/plutus-simple-model tutorial: https://mlabs-haskell.github.io/plutus-simple-model/ Cheers! Anton

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Capturing typeclass dictionaries from constructors
by Clinton Mead 05 Aug '22

05 Aug '22

Hi All I've asked the following question on StackOverflow, but I thought here might be a good place for it also. Sorry for the crosspost but I'm never sure what the best place to ask Haskell questions is: https://stackoverflow.com/questions/73244177/capturing-typeclass-dictionari… I've copied the StackOverflow post below: --- Below is code that will happily compile (once adding the constraints package). Foo1 and Foo2 are two alternate definitions of Foo, which I can write f1 and f2 sensibly for. However, I *think* Foo3 is reasonable as well. Yet I don't know how to write f3. It seems to me that Haskell should store a pointer to the typeclass dictionary inside the Foo3 constructor, for whatever a is passed when Foo3 is created, so then I should be able to just call silly. Since silly just returns String, it doesn't matter if a has been erased by now, I should be able to happily call the silly pointed to by the dictionary stored in the constructor Foo3. Is my reasoning right? And if so, how can I write f3. Alternative, have I missed something and is there a good reason why I need either Dict or Proxy here because without them I haven't got enough information? {-# LANGUAGE ScopedTypeVariables #-} import Data.Constraint (Dict(Dict), withDict)import Data.Proxy (Proxy) data Aliceclass C a where silly :: Stringinstance C Alice where silly = "Silly Alice" data Foo1 where Foo1 :: Dict (C a) -> Foo1 f1 :: Foo1 -> Stringf1 (Foo1 (dict :: Dict (C a))) = withDict dict $ silly @a data Foo2 where Foo2 :: C a => Proxy a -> Foo2 f2 :: Foo2 -> Stringf2 (Foo2 (_ :: Proxy a)) = silly @a data Foo3 where Foo3 :: C a => Foo3 mkFoo3 :: forall a. C a => Foo3mkFoo3 = Foo3 @a f3 :: Foo3 -> Stringf3 = undefined

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Re: [Haskell-cafe] [ANNOUNCE] GHC 9.4.1-rc1 is now available
by Kazu Yamamoto 02 Aug '22

02 Aug '22

Hi George, > I've duplicated the issue on both of my machines. It would be good to know > if anybody else is seeing it. Kazu, I know you have seen this in the past. > Do you get the same error installing rc1? > When I run sudo make install I get a popup that says: I had no problem on 9.4.1-rc1. "xattr -rc ." and "make install" worked perfectly. macOS Monterey v12.4 Xcode 13.4.1 --Kazu

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