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author | Profpatsch <mail@profpatsch.de> | 2021-01-23T16·23+0100 |
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committer | Profpatsch <mail@profpatsch.de> | 2021-01-30T15·41+0000 |
commit | e4a7704583812786d90ddc1f3aa639b2866e18e2 (patch) | |
tree | 47f47254f7b198813e151a71410864f50e91e919 /nix/runExecline/runExecline.nix | |
parent | 5da7ee9e8a7e3e790963b52f6427027a8823d75a (diff) |
feat(nix): add nix.tag, a way of discriminating via tagged unions r/2166
Introduces the concept of a “tag”, a single-keyed attrset which annotates a nix value with a name. This can be used to implement tagged unions (by implying the list of possible tags is well-known), which has some overlap with how `nix.yants` does it. However, the more fascinating use-case is in concert with a so-called discriminator, `match` and hylomorphisms. The discriminator can take a nix value, and add tags to it based on some predicate. With `match`, we can then use that information to convert the discriminated values again. With `hylo`, we can combine both the “constructive” discriminator step with the “destructive” match step to recursively walk over a nix data structure (based on a description of how to recurse, e.g. through attrset values or list values), and then apply a transformation in one go. Change-Id: Ia335ca8b0881447fbbcb6bcd80f49feb835f1715 Reviewed-on: https://cl.tvl.fyi/c/depot/+/2434 Tested-by: BuildkiteCI Reviewed-by: sterni <sternenseemann@systemli.org>
Diffstat (limited to 'nix/runExecline/runExecline.nix')
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