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Beady Belle Fanchannel

@Profpatsch@mastodon.xyz · 12 hours ago

I realized why I always thought `placeholder` was a weird primitive in the nix language: It breaks referential transparency!

> cat example.nix
with import <nixpkgs> {};
let
inner = txt: writeText "inner" txt;

in runCommand "outer" {} ''
(echo -n "placeholder result: "; cat ${inner (placeholder "out")}) \
> $out
<End of example.nix>
> cat (nix-build example.nix)
placeholder result: /nix/store/bnns37m7b4kiyqskxnfzka2jsj9byf9y-inner⏎ — > cat example.nix with import <nixpkgs> {}; let inner = txt: writeText "inner" txt; in runCommand "outer" {} '' (echo -n "placeholder result: "; cat ${inner (placeholder "out")}) \ > $out <End of example.nix> > cat (nix-build example.nix) placeholder result: /nix/store/bnns37m7b4kiyqskxnfzka2jsj9byf9y-inner⏎

1

Anselm "Two Sheds" Schüler

@anselmschueler@ieji.de replied · 12 hours ago

@Profpatsch What is this function? I can't find it in nixpkgs docs.

1

Anselm "Two Sheds" Schüler

@anselmschueler@ieji.de replied · 12 hours ago

@Profpatsch I see, it's a builtin

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