Editing User:Drostie (section)

== Subtyped metadata language ==
I'm reasonably sure that you can use subtyping to do arbitrary metadata (which is close to the way "mixins" work) with a type system. My goal there is to (a) make a programming language which is effortless at expressing metadata; (b) use that language's parse trees as its own data structure, so that every data structure also has metadata associated with it; (c) write the subtype-checker in the language itself; (d) offer a compiler which by default type-checks, but where this can easily be turned off.

If I were really optimistic I would then say that maybe we could support a really generic polymorphism, where technically 1 is ''defined'' as the Church number but there is metadata which tells the compiler that it's ''okay'' to store it as a bignum, or a long, or an int, or a short, or a byte, or a bit. The idea is that the language would entertain the notion of multiple perspectives on the same data, and would be able to lazily autoconvert between them ("You wanted to compute a multiplication? Okay -- switching to a decimal representation. Oh, now you want to repeat a function that many times? I've got a Church numeral for you...").

With a dynamically pluggable syntax, ideally we'd be able to translate the abstract parse trees (which are just data structures) from language to language, saying "here is the Python translation of what you wrote, here is the Haskell translation of what you wrote," etc. Then we tell the Pythonistas that they've secretly been programming in the new language all along, and here's a useful subtype-checker which they can use to make their code better -- oh, and if they want to use our libraries, that's cool too.