[Nix-dev] Re: NixOS: New scheme

[Ludovic Courtès]

Hi,

Marc Weber <marco-oweber at gmx.de> writes:

>> too coarse-grain, and it breaks the principle of least authority.  I
>
> In general this is good.

No it's not.  :-)

> I really fail to see what difference it makes as
> - the jobs are run as root anyway
> - the jobs can run rm -fr / as root as well..

This is not what I had in mind.  I was referring to PoLA in the context
of our "program" code, i.e., the Nix code in the NixOS repository.

If we were to make an analogy with a language like C, passing `pkgs'
and `config' to every function amounts to passing arguments using global
variables.

That is, instead of

  int
  do_things (pkg_t foo, pkg_t bar)
  {
    ...
  }

you would write:

  struct
  {
    pkg_t foo; pkg_t bar; pkg_t baz; pkg_t chbouib; ...
  } pkgs;

  int
  do_things (void)
  {
    /* Use `pkgs.foo', etc.  */
    ...
  }

As a functional programmer, you will surely agree that this is bad
programming style.  ;-)

A practical consequence is that it makes it very hard to read the code
and understand what a function does since it takes input data
implicitly, from "the environment".  It also makes it impossible to
"virtualize" functions: the second version of `do_things ()' will always
use the global `pkgs.foo' and cannot be told to use something else as
`foo'.  In the context of the Nix interpreter, it probably prevents
optimizations since it's as if every Upstart job depended on *all*
packages (perhaps Eelco can comment on this).

Thanks,
Ludo'.