>This is what we did with Dart's package manager[1]. It works like Bundler where it finds a single set of package versions that satisfy all of the constraints a

>This is what we did with Dart's package manager[1]. It works like Bundler where it finds a single set of package versions that satisfy all of the constraints and there are no duplicate packages. Constraint solving is the status quo, and I am strongly opposed to it. Rather than saying "I want foo >= 1.0" in a package manager, you should have the build system test the environment for the features you need. This is what the Autotools and other build systems that have been around for decades do. This way, the project isn't tied to a single package manager and, in the case of free software, greatly eases the burden on package maintainers that want to add your software to their distribution. Functional package management doesn't need constraint solving because every package in the system precisely describes itself: exactly which dependencies are needed for build-time and runtime (which precisely describe themselves, recursively, all the way down to libc), precisely which source code (tarball/directory/whatever + checksum), and the exact build script that turns that source code into a (hopefully bit-reproducible) binary. There's no constraint solving to determine what the dependency tree is, it's already been encoded in the package objects themselves. This is what any robust package manager should enable, but the only two that I know of that do this are Nix and GNU Guix. >The problem then is now your language has a dependency on an outside package manager, one which is often OS specific. Most modern languages need to support a variety of OSes. A programming language should not depend on any specific package manager. This is what build systems are for! More and more language communities conflate the two, but this is a huge mistake that we are paying for by making our software nearly impossible to reproduce from source code. [0] Everyone just uses pre-built binaries full of circular dependencies and reproducibility issues because things are so tangled that no one actually knows how to build anything from source anymore. I think the value of language-specific package managers lies in providing an easy way to fetch pure (no native code) modules to faciliate simple code sharing and helping newcomers get bootstrapped quickly. However, for serious software development and deployment they are terrible and we desperately need better tools. I think functional package managers are the tools we need, as they have greatly simplified software building and deployment for me whilst also greatly increasing the reliability of the systems that use them thanks to transactional upgrades and rollbacks. [0] http://www.vitavonni.de/blog/201503/2015031201-the-sad-state-of-sysadmin-in-the-age-of-containers.html http://www.vitavonni.de/blog/201503/2015031201-the-sad-state...