hablapps/DontFearTheProfunctorOptics
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Fixed minor typo.
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jon hanson 2022-08-10 13:15:56 +01:00 committed by GitHub
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@ -208,7 +208,7 @@ maybeFirst = Affine p st where
st (b, (ma, c)) = (ma $> b, c)
```
There's no always an `a` hidden behind this data structure. On the other hand, we can't build a whole `(Maybe b, c)` simply from a `b`. In fact, we need a `c` to do so. In addition, the affine laws make it impossible to update the focus if it didn't exist in the whole. Therefore, we need the complete `(Maybe a, c)` as contextual information. Next, we show a scenario where we run this optic:
There's not always an `a` hidden behind this data structure. On the other hand, we can't build a whole `(Maybe b, c)` simply from a `b`. In fact, we need a `c` to do so. In addition, the affine laws make it impossible to update the focus if it didn't exist in the whole. Therefore, we need the complete `(Maybe a, c)` as contextual information. Next, we show a scenario where we run this optic:
```haskell
λ> preview maybeFirst (Just 1, "hi")