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Merged
merged 9 commits into from
Sep 14, 2020
Merged

Fill out additional docs on things #28

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455487b
Clarify These type and what most type class instances operate on
JordanMartinez Sep 14, 2020
11fbaac
Document the `these` function
JordanMartinez Sep 14, 2020
c015b27
Document the `fromThese` function
JordanMartinez Sep 14, 2020
52d443e
Update changelog with PR's content
JordanMartinez Sep 14, 2020
24fff5e
Include author name in PR
JordanMartinez Sep 14, 2020
e507767
Reword the `fromThese` documentation
JordanMartinez Sep 14, 2020
9369b0c
Update docs for `these`
JordanMartinez Sep 14, 2020
e1e3213
Remove doc explaining that most TC instances work on the `b` type
JordanMartinez Sep 14, 2020
527ecd8
Fix grammatical mistake
JordanMartinez Sep 14, 2020
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3 changes: 3 additions & 0 deletions docs/CHANGELOG.md
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Expand Up @@ -11,5 +11,8 @@ New features:
Bugfixes:

Other improvements:
- Documented additional things (#28 by @JordanMartinez)
- `These` data type and a short description of how type class instances work
- `these` and `fromThese` functions

## [0.0.0] - 2020-01-01
10 changes: 10 additions & 0 deletions src/Data/These.purs
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Expand Up @@ -10,6 +10,10 @@ import Data.Maybe (Maybe(..), isJust)
import Data.Traversable (class Traversable, class Foldable, foldMap, foldl, foldr)
import Data.Tuple (Tuple(..))

-- | Data type isomorphic to `α ∨ β ∨ (α ∧ β)` or
-- | `Either a (Either b (Tuple a b))`.
-- |
-- | Most type classes instances work on the value of the `b` type.
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I'm not sure this line is needed, as this is the same Functor behavior that applies to any type with multiple type arguments.

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I think this line should become the new precedent because its helpful for new learners. However, I don't believe strongly in this either. Thoughts?

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I would prefer not to include it -- it's more important that new learners are able to associate this structure with Functor (or Bifunctor). For new learners I would rather have a brief example of using map with a These value in the quick start so they can begin to recognize a very wide-ranging pattern.

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Good point. Fixed

data These a b
= This a
| That b
Expand Down Expand Up @@ -98,6 +102,8 @@ instance showThese :: (Show a, Show b) => Show (These a b) where
show (That y) = "(That " <> show y <> ")"
show (Both x y) = "(Both " <> show x <> " " <> show y <> ")"

-- | Given functions to handle each constructor, collapse a `These` value
-- | into single value.
these :: forall a b c. (a -> c) -> (b -> c) -> (a -> b -> c) -> These a b -> c
these l _ _ (This a) = l a
these _ r _ (That x) = r x
Expand All @@ -119,6 +125,10 @@ maybeThese = case _, _ of
Just a, Just b -> Just (Both a b)
Nothing, Nothing -> Nothing

-- | Takes two default values and a `These` value. If the `These` value is
-- | `This` or `That`, the value wrapped in the `These` value and its
-- | corresponding default value are wrapped into a `Tuple`.
-- | Otherwise, the values stored in the `Both` is rewrapped into a `Tuple`.
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Suggested change
-- | corresponding default value are wrapped into a `Tuple`.
-- | Otherwise, the values stored in the `Both` is rewrapped into a `Tuple`.
-- | corresponding default value are wrapped into a `Tuple`. Otherwise, the
-- | values stored in the `Both` are re-wrapped into a `Tuple`.

Minor typo here ("values" -> "are")

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Fixed

fromThese :: forall a b. a -> b -> These a b -> Tuple a b
fromThese _ x (This a) = Tuple a x
fromThese a _ (That x) = Tuple a x
Expand Down