#607: Add missing Show instances

[matt-martin]

Randomly picked up this issue as I saw it was marked as "low hanging fruit" and I wanted to get more familiar with cats (and associated FP concepts).

One thing of note: I had to add a show instance for Tuple2 to make this work. I can't claim to be intimately familiar with Miles' Kittens project (see: https://github.com/milessabin/kittens), but it seemed like defining Show instances for Tuples and case classes would be particularly tedious and possibly something that Kittens/Shapeless could make a lot easier.

Without further ado, here is my initial attempt to address issue #607 and add a Show instance for WriterT.

[codecov-io]

Current coverage is 88.87%

Merging #928 into master will decrease coverage by -0.07% as of cabb413

@@            master    #928   diff @@
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  Files          179     179       
  Stmts         2125    2130     +5
  Branches        42      42       
  Methods          0       0       
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+ Hit           1890    1893     +3
  Partial          0       0       
- Missed         235     237     +2

Review entire Coverage Diff as of cabb413

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[ceedubs]

Wonderful 👍. Thanks @matt-martin!

See #631 for some discussion regarding the tuple instance generation that you brought up.

[stew]

👍

[matt-martin]

Thank you @stew and @ceedubs! Appreciate the reference to #631. Definitely interested in that discussion.

[adelbertc]

Hm we should be able to delete this line right?

[ceedubs]

@adelbertc isn't the Show instance delegating to this method?

[matt-martin]

Yeah, the Show instance is delegating to this method. I modeled this on the change that added a Show instance for OptionT (see: https://github.com/typelevel/cats/pull/600/files; and in particular:

cats/core/src/main/scala/cats/data/OptionT.scala

Line 90 in 6dbd4b0

def show(implicit F: Show[F[Option[A]]]): String = F.show(value)

). But I agree it is not strictly needed (assuming the Show instance is updated accordingly).

[adelbertc]

Oh I see now, I read it as Show[(L, V)] - ignore me :-)