Explain how to write Show instances

[neongreen]

A workaround I found: if you add import qualified Prelude to your module, suddenly you can write Show instances as usual.

[neongreen]

Look ma, no show:

> import Prelude (Show)
> show

<interactive>:2:1: error: Variable not in scope: show

Doesn't work:

> data Foo = Foo

> instance Show Foo where show Foo = Foo

<interactive>:3:25: error:
    ‘show’ is not a (visible) method of class ‘Show’

And now it does!

> import qualified Prelude
> instance Show Foo where show Foo = "Foo"

And show is still not in scope:

> show

<interactive>:8:1: error:
    • Variable not in scope: show

[gromakovsky]

Interesting, I thought it was somewhere in the docs, but apparently it never went beyond Slack discussions.

Since show doesn't come from Show anymore, you can't write Show instances easily.

Looks like a good place (in README) to write how one can do it not easily (but still it looks quite easy).

Btw, we've been doing import qualified Text.Show which looks a bit better because one can easier realize what this import is for.

[neongreen]

May you and your kin prosper for a thousand years

[gromakovsky]

@Martoon-00 did you close it by mistake?

[neongreen]

Oh

[gromakovsky]

Btw, we've been doing import qualified Text.Show which looks a bit better because one can easier realize what this import is for.

Another reason for it is that if you use base-noprelude or mixins to make Prelude refer to Universum (or your own custom prelude based on Universum), import qualified Prelude probably won't work. When we talk about custom preludes it sometimes might be the case that Prelude is not Prelude from base.

I guess I have spare 10 minutes to do this issue, a PR should come shortly.

[gromakovsky]

:nate: #228

[Martoon-00]

@Martoon-00 did you close it by mistake?

Yep, sorry :/