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Add Eq1 Ord1 to NonEmptyList LazyNonEmptyList #188

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merged 4 commits into from
Jan 14, 2021

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milesfrain
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@milesfrain milesfrain commented Jan 11, 2021

Description of the change

Adds Eq1 and Ord1 instances to NonEmptyList and LazyNonEmptyList
Fixes #186


Checklist:

  • Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
  • Linked any existing issues or proposals that this pull request should close
  • Updated or added relevant documentation
  • Added a test for the contribution (if applicable)

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CI shows that the Lazy version of this change fails to compile, but the non-Lazy version works fine. Don't know why.

@milesfrain milesfrain marked this pull request as ready for review January 11, 2021 08:37
@@ -211,6 +211,12 @@ derive instance newtypeNonEmptyList :: Newtype (NonEmptyList a) _
derive newtype instance eqNonEmptyList :: Eq a => Eq (NonEmptyList a)
derive newtype instance ordNonEmptyList :: Ord a => Ord (NonEmptyList a)

instance eq1NonEmptyList :: Eq1 NonEmptyList where
eq1 (NonEmptyList lhs) (NonEmptyList rhs) = eq1 lhs rhs
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Was hoping this shorthand would work, but it does not:

eq1 = over NonEmptyList eq1

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I've seen a number of cases where omitting arguments in an instance doesn't work. But I think it's arguably better to include the arguments explicitly in any case.

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@milesfrain milesfrain Jan 14, 2021

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I'd argue that the shorthand version is better, since it protects you from making a mistake like this:

compare1 (NonEmptyList rhs) (NonEmptyList lhs) = compare1 lhs rhs

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milesfrain commented Jan 14, 2021

Should these changes be tested, and if so, I guess I should also add the same tests to the empty-able lists too?
Also, holding off on editing the changelogs for each of these pending PRs, since that's going to cause a merge conflict after each PR is merged. Will do that right before 0.14

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I don’t think these need tests - the type system helps us enough here (via parametricity) that I think we can be confident these are doing the right thing without needing additional tests.

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hdgarrood commented Jan 14, 2021

Actually let’s include the changelog updates in each PR please; the merge conflicts that would be introduced will all be very easy to fix.

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Thank you!

@hdgarrood hdgarrood merged commit e992892 into purescript:master Jan 14, 2021
@milesfrain milesfrain deleted the non-empty-eq1-ord1 branch January 14, 2021 20:07
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Add Eq1 and Ord1 instances to NonEmptyList and LazyNonEmptyList
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