Implement Data.Reflectable

[purefunctor]

Closes #286. Adds a Data.Reflectable module which is where the compiler looks at for the automatically-solved Reflectable type class.

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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)

[JordanMartinez]

Could you add tests for both the Reflectable and Reifiable type classes?

[purefunctor]

Should I copy-paste the tests from the compiler? https://github.com/purescript/purescript/blob/1d5c618054bc0c452128e8758dc01b758a3a6f39/tests/purs/passing/SolvingReflectable.purs

I think testing Reflectable here would be a bit redundant given the compiler tests. Similarly, tests for IsSymbol is done there too. I'm fine with either way, though 😅

[JordanMartinez]

Should I copy-paste the tests from the compiler? https://github.com/purescript/purescript/blob/1d5c618054bc0c452128e8758dc01b758a3a6f39/tests/purs/passing/SolvingReflectable.purs

I think testing Reflectable here would be a bit redundant given the compiler tests. Similarly, tests for IsSymbol is done there too. I'm fine with either way, though 😅

I think adding it here forces other backends to also implement the tests, which aren't being tested in the compiler. We'd also probably want something more granular.

testReflection :: AlmostEff
testReflection = do
  assert "Symbol reflection" $ reflectType (Proxy :: Proxy "foo") == "foo"
  assert "Int reflection - 1" $ reflectType (Proxy :: Proxy 1) == 1
  assert "Int reflection - 0" $ reflectType (Proxy :: Proxy 0) == 0
  assert "Int reflection - (-1)" $ reflectType (Proxy :: Proxy (-1)) == (-1)
  assert "Boolean - True reflection" $ reflectType (Proxy :: Proxy PB.True) == true
  assert "Boolean - False reflection" $ reflectType (Proxy :: Proxy PB.False) == false
  assert "Ordering - LT reflection" $ reflectType (Proxy :: Proxy PO.LT) == LT
  assert "Ordering - EQ reflection" $ reflectType (Proxy :: Proxy PO.EQ) == EQ
  assert "Ordering - GT reflection" $ reflectType (Proxy :: Proxy PO.GT) == GT

Similarly for the Reifiable which isn't being tested by anything, right?

[JordanMartinez]

🏓 @thomashoneyman

[thomashoneyman]

👍 thanks, @purefunctor!