Put monomorphic functions into single parameter classes about string-conversions

[soenkehahn]

@c-t-k: Sorry, do you have a link to the documentation of ExtendedDefaultRules? Google is failing me right now.

So far I considered the use-case of string-conversions to be to convert between two concrete types of strings, e.g. String -> Text. It just uses a type class to overload cs. To make it easier to compose libraries that use different types.

It looks like you're trying to use it to write functions that are generic in the type of string they use. That is not what string-conversions was built to do. But maybe I'm also misunderstanding your use-case a bit. Could sketch a more concrete example for what you want to do?