The th-dict-discovery package

[ Tags: bsd3, language, library ] [ Propose Tags ]

th-dict-discovery is a library to get your hands on the in-scope, concrete instances of a class. The motivating use-case is to generate property tests to automatically prove new instances of a class follow the laws.

This library uses Template Haskell to provide a list of existentialized Dicts for each concrete (entirely monomorphic) instance in scope.

defInstances :: [SomeDict1 Default]
defInstances = $(someDicts ''Default)

These lists can be consumed via withSomeDict1 :: (forall a. c a => Proxy a -> r) -> SomeDict1 c -> r, for example, we can generate hspec tests:

spec :: Spec
spec = describe "each default instance" .
  forM_ defInstances $ withSomeDict1 $ \(_ :: Proxy a) ->
    it "shouldn't be undefined" $
      seq (def @a) True `shouldBe` True

The library also defines up to SomeDict8, with eliminators up to withSomeDict8. These correspond to multi-parameter typeclasses with first-order, potentially polykinded parameters.

The TH function someDicts is smart enough to generate the correct arity of SomeDictN for the class under inspection, but at this time, you're responsible for using the correct withSomeDictN to consume it.


Change log
Dependencies base (==4.9.*), constraints, template-haskell [details]
License BSD3
Author Sandy Maguire
Category Language
Home page
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Source repo head: git clone
Uploaded Wed Dec 27 09:54:45 UTC 2017 by isovector
Distributions NixOS:
Downloads 98 total (4 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by rule of succession]
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Status Docs not available [build log]
All reported builds failed as of 2017-12-27 [all 2 reports]
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  • Language
    • Haskell
      • Language.Haskell.Discovery


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