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A typeclass-based Prelude.

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A typeclass-based Prelude. For more information, see the blog posts:

A common question/criticism raised about classy-prelude goes like this: type classes have to have laws associated with them, and you can't just use typeclasses to give names to difference things. I'd like to address that (recurring) comment once, here.

There are many tools and language features (both in Haskell and other environments) that can be used for purposes other than their originally intended purposes. Examples include:

  • Using OverloadedStrings to express routing (Scotty does this).
  • Using a data markup language as a programming language (XSLT).
  • Compile-time static assertions using a generic programming technique (C++ and Boost).

The examples are quite numerous. Do I like all of these? No. Many people know that I happen to utterly despise XSLT. But it's not sufficient to say "it's using a declarative data format to write code, it's bad." Using a tool for a different purpose is not really an argument as to why something is bad.

Now there are plenty of reasons you may dislike classy-prelude. I listed some in my own blog post. And I myself said in that post that a real namespacing solution would be better. But in the interim, this is (AFAIK) the only approach that gives the same namespacing result, or at least a close approximate. If you don't want to use it, that's fine. And in fact, that's the whole reason CorePrelude exists: so that others can experiment with other ideas!

But the statement that "Classes shouldn't be used just to be able to reuse the same name" is purely a subjective argument, and lacks any kind of explanation as to why you believe it. I'm happy to hear developed arguments for this, but such an assertion doesn't really further the discussion at all.

(Also, FWIW, classy-prelude is not the first time that type classes don't have associated laws. An example straight from base is IsString.)

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