6 ms·

nixpkgs.lib has mkDefault/mkForce/mkOverride system (which I'm not a fond of because of the poor type system, but at least it works) that feels like a better ap

nixpkgs.lib has mkDefault/mkForce/mkOverride system (which I'm not a fond of because of the poor type system, but at least it works) that feels like a better approach than this weirdness.

soraminazuki 2y ago
The Nixpkgs module system that you're describing does have types though. The whole purpose of that system is to attach types and documentation to data.
- drdaeman 2y ago
  Unless I'm misunderstanding how it all works, it's just attrsets underneath. Like JSON objects with some semantics given to them - and those (and their YAML counterparts) are not exactly great. In particular, I believe (I could be wrong here) this results in sometimes hard-to-understand error traces if something gets messed up.
  - soraminazuki 2y ago
    The module system type checks each attribute in a attrset. It merges all modules, ensures there are no conflicts, type checks and returns the resulting attrset. Error messages indicate the offending option definition along with its location in the case of conflicts or type errors, which should be enough for enough for debugging.
    - drdaeman 2y ago
      I vaguely remember shooting myself in my foot by doing some weird stuff with deep attrset transformations, where I managed to screw-up those "special" attrsets by making a mistake in a function that tried to build module options dynamically from another "transplant" module's options. Surely, that was weird stuff, and sadly I don't have a history of what exactly I did back then (it was couple years ago), but I remember having to introspect with Nix REPL to understand where I messed up. I would've loved it more if Nix had ability to create custom types, ideally GADTs. Tagged attrsets work for sure, but a better type system would've probably made things easier and nicer.
yjftsjthsd-h 2y ago
ansible has what I think is a sort of similar system, where a role can define default values for its variables but they can be overridden in a fairly deep hierarchy of successive priorities; it helps that the lowest tier is literally labeled "defaults" so you automatically expect it to be overwritten, though in the upper layers I still have to look up to see which thing takes precedence.
- soraminazuki 2y ago
  The merging behavior of Nixpkgs modules are much simpler. It doesn't have orders or complex priority rules that depend on where an option is defined. Options have types, which also specifies the merging behavior. Merging of collection types just work.

nixpkgs.lib has mkDefault/mkForce/mkOverride system (which I'm not a fond of because of the poor type system, but at least it works) that feels like a better approach than this weirdness.

soraminazuki 2y ago

The Nixpkgs module system that you're describing does have types though. The whole purpose of that system is to attach types and documentation to data.

drdaeman 2y ago
Unless I'm misunderstanding how it all works, it's just attrsets underneath. Like JSON objects with some semantics given to them - and those (and their YAML counterparts) are not exactly great. In particular, I believe (I could be wrong here) this results in sometimes hard-to-understand error traces if something gets messed up.
- soraminazuki 2y ago
  The module system type checks each attribute in a attrset. It merges all modules, ensures there are no conflicts, type checks and returns the resulting attrset. Error messages indicate the offending option definition along with its location in the case of conflicts or type errors, which should be enough for enough for debugging.
  - drdaeman 2y ago
    I vaguely remember shooting myself in my foot by doing some weird stuff with deep attrset transformations, where I managed to screw-up those "special" attrsets by making a mistake in a function that tried to build module options dynamically from another "transplant" module's options. Surely, that was weird stuff, and sadly I don't have a history of what exactly I did back then (it was couple years ago), but I remember having to introspect with Nix REPL to understand where I messed up. I would've loved it more if Nix had ability to create custom types, ideally GADTs. Tagged attrsets work for sure, but a better type system would've probably made things easier and nicer.

yjftsjthsd-h 2y ago

ansible has what I think is a sort of similar system, where a role can define default values for its variables but they can be overridden in a fairly deep hierarchy of successive priorities; it helps that the lowest tier is literally labeled "defaults" so you automatically expect it to be overwritten, though in the upper layers I still have to look up to see which thing takes precedence.

soraminazuki 2y ago
The merging behavior of Nixpkgs modules are much simpler. It doesn't have orders or complex priority rules that depend on where an option is defined. Options have types, which also specifies the merging behavior. Merging of collection types just work.