Replace ocamlyacc with cpspg

[adampsz]

This PR replaces ocamlyacc with fram-lang/cpspg@67dfc0f to check its compatibility and experiment with the new parser generator tool.

Building now requires cpspg to be in the path - it can be dune build and dune install-ed from adampsz/cpspg repo.

[ppolesiuk]

Thanks! This PR opens new perspectives for a better parser. However, I cannot merge it yet, since it breaks CI.

[ppolesiuk]

Should we remove this line instead of commenting it out? As discussed on the last meeting, we are going to use nice features of cpspg (which are not implemented yet), so I think in the near future, we will be incompatible with ocamlyacc.

[ppolesiuk]

Does cpspg generate .mli files? If yes, maybe it should be added to this rule (I'm sure, dune can do that. You can ask @Foxinio, our local dune guru). If not, maybe we could consider writing own YaccParser.mli file.

[adampsz]

It does not generate .mli files, but it should be straightforward to implement.

[Brychlikov]

I got CI to work using nix here. I packaged both dbl and cpspg as flakes.
For now, I had to make two changes:

• test.sh doesn't try to run dune build
• changed its first parameter so it now should be something in PATH or be a path to dbl binary

[ppolesiuk]

I see a minor problem with this change. When I run tests locally, I would like to use a version of dbl compiled from source on the active branch, not the one that is installed on my system.

[Brychlikov]

A bit of an oversight on my part - in my dev environment, dbl in PATH is the one from _build/.... To be fair, you still can run ./test.sh ./_build/default/src/dbl.exe ./test/test_suite to test against your freshly built dbl, but I understand that the default workflow should probably remain unchanged.

[Brychlikov]

I restored most of the original behaviour of test.sh in my branch - when passed a relative path as PROGRAM it does what it used to do.