Yes, or a full-featured programming language. Even though I don't really know or like Ruby, I still like that Vagrant uses it for config since it is at least possible to do complex things if you need to.
It makes it impossible for the system to reason about the outputs though (due to the halting problem and a lot of other practical issues). Therefore a Vagrant setup just "does its best" to execute the given prescription to set a machine up, whereas something like Terraform will actually intelligently figure out if work needs to be done.
I don't understand why you have been downvoted. Many of these tools are very imperative and make assumptions about the starting state before they replay their updates. For a fully declarative solution, NixOS is the best I have seen.
This is a strange assertion--you run the DSL to generate, at runtime, a data model that can then be checked. Hell, I wrote a Terraform competitor that was certainly no worse at planning than Terraform is. (Still not great, because the problem is a hard one, but.)
And doing so gives you such niceties as if-statements and loops (I mean, have you seen the straight nonsense people have to pull to make a simple 'if' in HCL?) as well as a seamless way to introduce external data sources. This is why Chef remains the only part of my workflow that has not changed over the last five years (and why first Puppet and, eventually, Ansible will fall by the wayside): because, as a programming language and set of libraries, I can bring it with me by extending it at the user level without having to extend the runtime to do something. Patching the runtime means I need CM for my CM; doing it at the user level means it goes with me and plays with the base tools.
> Hell, I wrote a Terraform competitor that was certainly no worse at planning than Terraform is.
So why is Terraform so popular instead of your tool? :)
Both approaches have tradeoffs, and what you've mentioned are clearly advantages of the full-PL config style. The problem with a full-blown programming language, though, is that the flexibility makes it more difficult to reason about effects without actually running the code. If you're just using it to generate a declarative data model that then gets applied, you're still doing fully declarative management, just with extra steps.
It's not _necessarily_ a good thing to have something like if conditionals in a provisioning system either - the goal with these systems is usually to reduce uncertainty about outcomes, not multiply the # of branches you need to reason about. Ultimately I agree Terraform has issues with restrictions of HCL, but I don't think I'd say choosing a programming language instead of a purely declarative style is a no-brainer.
In favor of Ansible, I'd argue that extending it is trivial.
I tend to write simple Jinja2 filters when I need something done quickly that's not included, and it's as simple as making a specifically named directory (filter_plugins) and a python class (FilterModule). You can write your own modules pretty simply as well but there's a bit more boilerplate.
Considering that Vagrant is their most famous tool so far, they should have had a good reason to move to HCL then right? (And they do, as linked in a sibling comment.)