[Nix-dev] Re: environment.systemPackages

[Eelco Dolstra]

Hi,

On 03/04/2011 04:34 PM, Benjamin Franksen wrote:

> Eelco Dolstra wrote:
>>> How can I make the pkgs variable visible here?
>>
>> Add the following line to the top of the file:
>>
>>     { pkgs, ... }:
>>
>> Lots of examples of configurations can be found here:
>> https://svn.nixos.org/repos/nix/configurations/trunk/
>
> Thanks. I looked at these examples and saw such a line but, well... I just
> didn't think this could work. I mean, with this addition
> /etc/nixos/configuration.nix becomes a function, right? Is there a special
> trick that makes nixos interpret the code as either a function or a plain
> value?

Yes, there is, which is rather ugly :-)  Basically modules are called by 
doing

   if builtins.isFunction module
   then module { ... args ... }
   else module

But this is really for backwards compatibility.  It's best to always 
write modules as functions.

> Please forgive my beginner's confusion, I have some problems groking the nix
> language (the only functional languages I know are all statically typed).

Indeed we can get away with this only because we don't have static typing.

-- 
Eelco Dolstra | http://www.st.ewi.tudelft.nl/~dolstra/