Issue 42

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News from the Haskell community

  • Stackage LTS 8.0

    This is the first Stackage LTS snapshot with GHC 8.0.2.

  • GHC generics explained

    This tutorial will get you up to speed with GHC generics quickly. It should be noted that generics is not something academic and useless, quite the contrary, it’s a very pragmatic way to reduce the amount of boilerplate (and associated with it errors) in your functional code with minimal mental overhead.

  • Haskell on Bash/WSL

    Haskell is a popular and powerful functional programming language which wasn’t able to run on Bash/WSL in Anniversary Update or earlier Insider builds, because WSL had not yet implemented the timer_create() syscall. Now that WSL builds >= #14986 do support timer_create() we can run Haskell and many other tools (e.g. Elm, Cabal, Pandoc, Agda, etc.).

  • Stricter JSON parsing with Haskell and Aeson

    However, as this nice tour of how Aeson works demonstrate, if the input has keys that we don’t recognise, no error will be raised. This behaviour would not be undesirable in use-cases such as mine; if the client is sending fields we don’t understand, I’d like for the server to signal an error so the underlying problem can be caught early.

  • Replacing GHCi’s pretty-printer

    Luckily, GHCi is quite configurable! Using the -interactive-print flag, We can replace IO.print as the pretty-printer of choice, and slot in any function we please. My favourite alternative pretty-printer is Iavor Diatchki’s wonderful pretty-show, which uses a Haskell lexer.

  • Aelve Guide: Haskell CPP

    With {-# LANGUAGE CPP #-} enabled, .hs files will be processed with C preprocessor before the code is compiled.

  • Better exception messages

    When you throw an exception in your code, whether it be via throwIO, returning Left, using fail, or using error, please give us some context. During development, it’s a pain to have to dive into the code, add some trace statements, figure out what the actual problem is, and then remove the trace statements.

Package of the week

This week’s package of the week is hip, a Haskell image processing library.

Send us a message on Twitter to nominate next week’s package!