Packages are not installed globally in opam by default nowadays. `opam switch` "enables the user to have several installations on disk, each with their own prefix, set of installed packages, compiler version, etc".
https://opam.ocaml.org/doc/Usage.html#opam-switch
Do you have to run this command manually, and does it mutate the shell state? That's one thing that frustrated me with opam in the past as well. I couldn't just jump into a directory and build a thing, then switch to another project directory - there was a lot of manual switching and unswitching of packages if I recall correct?
Is it possible to install multiple tools globally using opam that use disjoint library versions? Like, I might want to install Abella and Coq side-by-side, but they might have conflicting version requirements. I think I was super excited about opam 2, then tried installing one thing, only to have it break again when I installed something else.
Is it possible to have multiple versions of the same libray in the same project, or does the constraint solver need to find a single solution for each library? [1]
Sorry I miss your reply. I create opam switches to have different versions of compiler, or allow libraries that conflict to live at different branches.
1. Dune is a relative new build system for Ocaml. You just write a configuration file, and dune will handle switches automatically. "It also supports multi-context builds, such as building against several opam roots/switches simultaneously. This helps maintaining packages across several versions of OCaml and gives cross-compilation for free." See https://opam.ocaml.org/packages/dune/
2. Yes. You can can multiple versions library at different switch.
