[Hasnep]

It's not the Nix/Guile that's expensive, it's situations like:

    let chromium = pkgs.chromium; in 1 + 1

In a maximally eager language you'd need to wait for the entirety of Chromium to build before you can find out what 1 + 1 is.

[atiedebee]

I checked the spec and Scheme R5RS does have lazy evaluation in the form of promises using "delay" and "force", but I can see why explicitly having to put those everywhere isn't a good solution.