Hi!
[email protected] (Ludovic Courtès) writes:
> --8<---------------cut here---------------start------------->8---
> let x = derivation {
> name = "x"; builder = ./foo.sh; system = builtins.currentSystem;
> };
> y = { b = x; };
> in
> x // y
> --8<---------------cut here---------------end--------------->8---
>
> Running ‘nix-instantiate --strict --eval-only --xml’ yields this:
>
> --8<---------------cut here---------------start------------->8---
> <?xml version='1.0' encoding='utf-8'?>
> <expr>
> <derivation drvPath="/nix/store/b1pmg2fhxnlnxy0z9hfglgyk66wpa2ar-x.drv"
> outPath="/nix/store/fw6flnp42lqn9i62aknpch29sadds5pi-x">
> <attr column="11" line="2" name="b"
> path="/home/ludo/src/nixpkgs/maintainers/scripts/gnu/self-ref.nix">
> <derivation drvPath="/nix/store/b1pmg2fhxnlnxy0z9hfglgyk66wpa2ar-x.drv"
> outPath="/nix/store/fw6flnp42lqn9i62aknpch29sadds5pi-x">
> <repeated />
> </derivation>
> </attr>
>
> [...]
>
> </derivation>
> </expr>
> --8<---------------cut here---------------end--------------->8---
Actually, isn’t this XML representation ambiguous?
It could just as well represent:
let x = derivation {
name = "x"; builder = ./foo.sh; system = builtins.currentSystem;
b = x;
};
in x
though this one obviously leads to an infinite recursion.
In Nix derivations aren’t a disjoint type, but in the XML above they
/are/ disjoint.
Thanks,
Ludo’.
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