Baldur Blöndal
Andres Löh
ABSTRACT
Haskell's deriving construct is a cheap and cheerful way to quickly generate instances of type classes that follow common patterns. But at present, there is only a subset of such type class patterns that deriving supports, and if a particular class lies outside of this subset, then one cannot derive it at all, with no alternative except for laboriously declaring the instances by hand.
To overcome this deficit, we introduce Deriving Via, an extension to deriving that enables programmers to compose instances from named programming patterns, thereby turning deriving into a high-level domain-specific language for defining instances. Deriving Via leverages newtypes---an already familiar tool of the Haskell trade---to declare recurring patterns in a way that both feels natural and allows a high degree of abstraction.
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Index Terms
- Deriving via: or, how to turn hand-written instances into an anti-pattern
Recommendations
Deriving via: or, how to turn hand-written instances into an anti-pattern
Haskell '18Haskell's deriving construct is a cheap and cheerful way to quickly generate instances of type classes that follow common patterns. But at present, there is only a subset of such type class patterns that deriving supports, and if a particular class lies ...
A generic deriving mechanism for Haskell
Haskell '10: Proceedings of the third ACM Haskell symposium on HaskellHaskell's deriving mechanism supports the automatic generation of instances for a number of functions. The Haskell 98 Report only specifies how to generate instances for the Eq, Ord, Enum, Bounded, Show, and Read classes. The description of how to ...
A generic deriving mechanism for Haskell
HASKELL '10Haskell's deriving mechanism supports the automatic generation of instances for a number of functions. The Haskell 98 Report only specifies how to generate instances for the Eq, Ord, Enum, Bounded, Show, and Read classes. The description of how to ...
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