September 2022 - Libraries

Proposal: add laws to MonadError
by Alexandre Esteves 06 Jul '23

06 Jul '23

I ran into a scenario where the use of MonadError would only be valid if catchError (pure a) h = pure a was a law, so I looked up the laws in https://hackage.haskell.org/package/mtl-2.3/docs/Control-Monad-Error-Class.… but surprisingly found none. One would expect to see 1. catchError (pure a) h = pure a 2. catchError (throwError e) h = h e 3. throwError e >>= f = throwError e which would rule out silly instances like instance MonadError () Maybe where throwError () = Nothing catchError _ f = f () Searching for "monad error laws" gives me no haskell results, only https://typelevel.org/blog/2018/04/13/rethinking-monaderror.html which suggests the same laws. I propose adding these 3 laws to MonadError haddocks. AFAICT the IO/Maybe/Either/ExceptT instances in https://hackage.haskell.org/package/mtl-2.3/docs/src/Control.Monad.Error.Cl… all obey the laws.

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characterization of subset of Monads that respect tail calls?
by Carter Schonwald 28 Sep '22

28 Sep '22

Hello everyone! a recent conversation I has having led to an interesting question: is there a good interface or something for Monads which guarantee tail calls are tail calls? (ideally via a stronger api assumption for tail position computations in a monad rather than "trustme" style api contracts) thx -Carter

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Maintaining lambdabot and dice
by Naïm Favier 27 Sep '22

27 Sep '22

I'd like to take over maintainership of the dice and lambdabot packages so that I can take care of GHC 9 support (https://github.com/lambdabot/dice/pull/2 and https://github.com/lambdabot/lambdabot/pull/204) The GitHub repo has been inactive since November 2021. I have contacted the current maintainer on IRC, where he is active, but he hasn't answered. Cheers

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Seeking a new maintainer for Edison
by Rob 11 Sep '22

11 Sep '22

I have for some time now been the nominal maintainer of the Edison collection of libraries, which consist of a variety of data-structure implementations originally derived from Chris Okasaki’s book “Purely Functional Data Structures.” See: https://hackage.haskell.org/package/EdisonAPI https://hackage.haskell.org/package/EdisonCore This library has recently received less attention than it probably deserves as I do not have the time or energy to devote to it. As such, I’m looking for a new maintainer who is willing to take up the mantle. Please reach out if you are interested in taking over. Cheers, Rob

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