Ada is not a mess. C89 was not a mess. Almost all languages become a mess when the become older or when standard committees are involved. For C++ it was a mess very early. After C++98, it was an awful mess of compiler incompatibilities. Strangely, a usable language seems to have recently emerged from this mess.

The ones that nobody improves.

Either because they are new, because nobody use them, or because they are LISP.

I really don't like how no lisper thinks it's a good idea to improve LISP, but it's this way.

I'll just state the obvious: Scheme. ;)

And Unlambda.

Joking aside, Haskell is pretty pleasant to program in most of the time.

forcing strict evaluation feels like a mess, template haskell feels like a mess, debugging space leaks feels like a mess, not to mention that the haskell learning curve is very high

Haskell is pretty good at a lot of things, so don't misunderstand me, Haskell it's really good! But, at the same time, it still has lots of room for improvement. I guess perfection doesn't exist.

Oh, there's room for improvement. I guess we just used different standards for `mess'.

I think something like http://lambda-the-ultimate.org/node/1446 could be the way forward. (And would be achievable from Haskell with enough work.)

Everyone and their grandma recommends me Scheme, but i am more willing to try a lisp that i can actually use in production like Clojure, i don't know.

The assertion was "not a mess," not "usable in production." ;)

Touché ;).

Why is Scheme unusable for production?

I wouldn't even think where i would use it, can you enlighten me?

Scheme with the batteries included:

http://racket-lang.org/