Revise Principles

[magnus-madsen]

• Rename fashion-driven to "Timeless"
• Move up "no blessed library".
• Rename "No dead or unreachable code" to "No unused declarations"
• Monotonic declarations.
• Layered programming language (functions, parametric polymorphism, type classes)
• Type class principles.

[mlutze]

I have a few nitpicks regarding the type class principles.

For the Explicit Override principle:

This ensures that there are no dangling overrides, i.e. functions definitions that do not match any signature of the type class.

This check happens, but it's not directly related to the override modifier.

Instead, the override modifier ensures:

• the user does not unknowingly re-implement something that already has a default implementation (required explicit override)
• the user does not just put override modifiers everywhere, making them meaningless (no overriding when there's no default)

Regarding the Default Implementations principle:

... can always be overridden ... For example, to provide a more efficient version.

Do we want to strengthen this or the override principle to say that an override must be observationally equivalent to the default implementation?