History

Profpatsch 4af195c5f2 feat(nix/yants): add restrict `restrict` uses a predicate function to restrict a type, giving the restricting a descriptive name in the process. First, the wrapped type definition is checked (e.g. int) and then the value is checked with the predicate, so the predicate can already depend on the value being of the wrapped type. Change-Id: Ic3edde45a8f34c31bc164414580d0a1aa5a821d5 Reviewed-on: https://cl.tvl.fyi/c/depot/+/2312 Tested-by: BuildkiteCI Reviewed-by: Profpatsch <mail@profpatsch.de> Reviewed-by: tazjin <mail@tazj.in>		2021-01-03 15:53:18 +00:00
..
screenshots	chore(yants): Prepare for depot-merge	2019-12-20 21:46:59 +00:00
tests	feat(nix/yants): add restrict	2021-01-03 15:53:18 +00:00
default.nix	feat(nix/yants): add restrict	2021-01-03 15:53:18 +00:00
README.md	docs(nix/yants): Mention Yants subtree split in README	2020-05-16 12:37:12 +01:00

README.md

yants

This is a tiny type-checker for data in Nix, written in Nix.

Features

Checking of primitive types (int, string etc.)
Checking polymorphic types (option, list, either)
Defining & checking struct/record types
Defining & matching enum types
Defining & matching sum types
Defining function signatures (including curried functions)
Types are composable! option string! list (either int (option float))!
Type errors also compose!

Currently lacking:

Any kind of inference
Convenient syntax for attribute-set function signatures

Primitives & simple polymorphism

Structs

Nested structs!

Enums!

Functions!

Usage

Yants can be imported from its default.nix. A single attribute (lib) can be passed, which will otherwise be imported from <nixpkgs>.

TIP: You do not need to clone my whole repository to use Yants! It is split out into the nix/yants branch which you can clone with, for example, git clone -b nix/yants https://git.tazj.in yants.

Examples for the most common import methods would be:

Import into scope with with:

with (import ./default.nix {});
# ... Nix code that uses yants ...

Import as a named variable:

let yants = import ./default.nix {};
in yants.string "foo" # or other uses ...

Overlay into pkgs.lib:

# wherever you import your package set (e.g. from <nixpkgs>):
import <nixpkgs> {
  overlays = [
    (self: super: {
      lib = super.lib // { yants = import ./default.nix { inherit (super) lib; }; };
    })
  ];
}

# yants now lives at lib.yants, besides the other library functions!

Please see my Nix one-pager for more generic information about the Nix language and what the above constructs mean.

Stability

The current API of Yants is not yet considered stable, but it works fine and should continue to do so even if used at an older version.

Yants' tests use Nix versions above 2.2 - compatibility with older versions is not guaranteed.