When comparing OCaml vs Vala, the Slant community recommends Vala for most people. In the question“What are the best languages to write a desktop Linux application in?” Vala is ranked 3rd while OCaml is ranked 5th. The most important reason people chose Vala is:
Vala developed by Gnome Foundation.
Ranked in these QuestionsQuestion Ranking
Pro Encourages functional style
It steers you towards a functional style, but doesn't bother you with purity and "monads everywhere" like other languages, such as Haskell.
Pro Actively-developed functional programming language at the forefront of research
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.
Pro Sophisticated and easy-to-use package manager
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.
Pro One of the best for writing compilers
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.
Pro Stable syntax
The syntax is consistent, some syntaxic sugar but at a reasonable level, so reading code of others isn't too much confusing.
Pro Strong editor integration
merlin editor tool provides all you need to develop OCaml in your favourite editor.
Pro Rich GTK Support
Vala developed by Gnome Foundation.
Underneath there is C. It makes some stuff easier to write than it would be with plain C code.
Pro Easy Syntax
Vala is syntactically similar to C# and includes several features such as: anonymous functions, signals, properties, generics, assisted memory management, exception handling, type inference, and foreach statements
Pro Well-integrated with C language
Vala itself is compiled to C, therefore it can use the vast ecosystem of C language, with least effort.
Pro Good documentation
There is Valadoc and most of the libraries have Devhelp packages.
Con Strong focus on *nix systems, lacking native support for MS Windows
Lacks native support for Windows systems.
Con Not a general purpose language
Can't use Vala in multiple software development areas.
Con Not well documented
It already has tons of documentation, even a book about Vala.https://leanpub.com/vala https://wiki.gnome.org/Projects/Vala/Documentation
Con Difficult to debug programs
Try Debug in Gnome Builder, it works perfectly.
Con Scarce learning resources
Difficult to find good resources for learning Vala.
Con Very few resources allocated to the language
Only a single person is working on Vala full time. Gnome Foundation isn't allocating sufficient resources to properly maintain Vala.
Con Doesn't have an independent type system
Heavy reliance on GObject types which heavily restricts where Vala can be used.
Con No stable version
No stable version of Vala released for over a decade so far. Means that Vala isn't production ready.
Con Very limited adoption
Vala isn't used in areas other than GTK development, and no major business has adopted the language.
Con Very limited tooling
Though using Gnome Builder, you can debug it easily.