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Many type class instances look ad-hoc, but are in fact adhering to implicit rules that allow the construction of instances based on other instances under certain conditions. Such rules currently have to be applied and instantiated manually, and many of them are not widely known as a consequence.
A new Haskell language extension in GHC (available from version 8.6) that allows such general rules to be given names (interestingly, by reusing the Haskell concept of "newtypes") and then instantiated in a "Deriving Via" clause. This means that many Haskell instances that previously had to be produced manually in a tedious and error-prone way now become one-liners.
In this talk, Andres will look at a number of examples where instances that occur "in the wild" can be simplified by means of Deriving Via, and he will also demonstrate some of the more surprising implications of this extension.
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Andres Löh is a Haskell consultant and co-owner of Well-Typed LLP. He is based in Regensburg, Germany. He started using Haskell in 1997, when being an undergraduate student of mathematics in Konstanz and has been an enthusiastic functional programmer ever since. Andres obtained a PhD in Computer Science from Utrecht University in 2004, on extending the Haskell language with capabilities for datatype-generic programming. After having been a university lecturer for several years, he joined Well-Typed in 2010.