hablapps/DontFearTheProfunctorOptics
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Merge pull request #7 from yuanw/issue-6

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Add comment about instantiate the profunctor family for DownStar

closes #6
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Jesús López-González 2019-01-14 11:34:54 +01:00 committed by GitHub
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Profunctors.md
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@ -317,6 +317,8 @@ parameter type) as an exercise:
newtype DownStar f a b = DownStar { runDownStar :: f a -> b }
```
(You may not able instantiate all three classes for `DownStar`. If so, try to reason about why certain class cannot be instantiated.)
Take [`Tagged`](http://oleg.fi/gists/posts/2017-04-18-glassery.html) as another
example: