[eigengrau]

> You can't print anything because the language is lazy. Forcing any values to print them can and will result in random operations happening on your store. You can never know which values are safe to inspect. This kills debugging.

I don’t quite follow the conclusion. Forcing values will not result in random operations on the store. Forcing values can only ever create store derivations, which is an internal representation of all derivations that were encountered while evaluating some expression. I won’t ever mutate existing data or remove anything from the store, nor will it actually build anything or fetch cached packages, so forcing values should be unproblematic. Store derivations can later be garbage collected.

[light_hue_1]

Yes. So, if I force a value, like say, I very naively do what I would do in any other programming language, I try to print something I don't understand (How are all of the python derivations stored, I wonder if I can print them?), the result is that I create endless garbage and .. sit there pointlessly looking at an empty screen. Evaluating derivations shouldn't result in work being performed. It should result in derivations being printed to the screen.

But.. it doesn't really matter that much because half of the datastructures in Nix are so circular that you couldn't print them out anyway.