OCaml vs Qt / C++

Functional programming is based on the lambda calculus. OCaml is in its functional parts almost pure lambda calculus, in a very practical manner: useful for many daily programming tasks. The acitve development makes improvements to the type system like generalized algebraic data types (GADT) or polymorphic variants, so when learning this language you get at once a down to earth usable compiler and advanced abstraction features.

It steers you towards a functional style, but doesn't bother you with purity and "monads everywhere" like other languages, such as Haskell.

Strong focus on *nix systems, lacking native support for MS Windows
Lacks native support for Windows systems.

OPAM is a package manager for OCaml, which is really easy to use, just like npm. It creates a .opam folder in home directory.

The documentation is great as well, and you can switch between multiple versions of OCaml for each project. You can also package your project and publish it on OPAM repositories, even if the dependencies do not exists on OPAM.

OCaml is compiled to native binary, so it's amazingly fast. Being a member of ML-family languages, it has expressive syntax for trees, and has great LLVM support.

The syntax is consistent, some syntaxic sugar but at a reasonable level, so reading code of others isn't too much confusing.

The merlin editor tool provides all you need to develop OCaml in your favourite editor.

Professional, thorough documentation with examples, available either in a web browser or in the stand-alone desktop client called assistant.

Linux, BSD, Android, iOS, Windows, Mac, Blackberry ... Qt has 'em all.

The community behind Qt is both massive and approachable. Digia (also owners) are joined by the likes of Intel, KDAB, ICS, Canonical and numerous others in sponsoring development, while communities such as KDE also contribute significantly. Forums are active, mailing lists are open, irc channels chatting, git repositories well managed. Answers to questions are usually minutes away.

QML is "HTML5 done right": a declarative language that integrates beautifully with C++ code when necessary and exposes the power of the GPU ... simply the best way to create a modern GUI in terms of effort and results.

Qt is licensed under a OSS license through a dual-license policy.