ToParamSchema class

[fizruk]

Closes #16.

This PR is incomplete.

[fizruk]

So here's some design problem:

We have Param, Items and Header all pretty similar:

• Header is exactly Items with description;
• Items is a restricted Param (without location, allowEmptyValue and without file type).

So we can probably factor out the common part (Items) and only consider that for a class (ignoring location).

[fizruk]

Okay, so I've moved type, format and items to SchemaCommon.
Now it represents the thing we should make a class for, that can be used for Param, Items and Header.

At this moment I realize that Schema also has SchemaCommon and that we can have something like this:

class ToSchemaCommon a t i where
  toSchemaCommon :: proxy a -> SchemaCommon t i

-- | Generate a 'NamedSchema' for a type with 'ToSchemaCommon' instance.
-- This can be used as an implementation of `toNamedSchema` for plain types.
toNamedSchemaCommon ::
  (..., ToSchemaCommon a (SwaggerType Schema) SchemaItems)
  => proxy a -> NamedSchema
toNamedSchemaCommon _ =
  ( genericToName (Proxy :: Proxy a)
  , mempty & schemaSchemaCommon .~ toSchemaCommon (Proxy :: Proxy a) )

With toNamedSchemaCommon it should be possible to avoid some code duplication (for non-object schemas):

instance ToSchemaCommon Bool t i where ...

instance ToSchema Bool where toNamedSchema = toNamedSchemaCommon

[dmjio]

That's fine with me.

[fizruk]

I think the PR is ready for merge.

@dmjio please, take a look.

Once this one is merged I am going for resolving #13.
Then the package should finally be ready to be used in servant-swagger.

[dmjio]

👍