Unhelpful error with associated types

In [this stackoverflow question](https://stackoverflow.com/q/68896181/15207568) the asker presents this code:

```haskell
{-# LANGUAGE TypeFamilies #-}

class Reproductive a where

-- | A sequence of genetic information for an agent.
type Strand a

-- | Full set (both strands) of genetic information for an organism.
type Genome a = (Strand a, Strand a)
```

But this produces the unhelpful error message (I was confused for a minute):

```
Assoc.hs:20:8: error:
‘Genome’ is not a (visible) associated type of class ‘Reproductive’
|
20 | type Genome a = (Strand a, Strand a)
| ^^^^^^
```

As a user I'm thinking that I'm defining an associated type, but this error message says that it expects the type to already be defined.

I now understand that you can easily solve this by writing a separate "kind signature" where the signature part can be omitted because it defaults to `*`:

```haskell
{-# LANGUAGE TypeFamilies #-}

class Reproductive a where

-- | A sequence of genetic information for an agent.
type Strand a

-- | Full set (both strands) of genetic information for an organism.
type Genome a
type Genome a = (Strand a, Strand a)
```

I think this warning can be improved, but I'm not sure how, yet.