Create a scope variable in `nix repl`

[Denommus]

Is your feature request related to a problem? Please describe.
I was using node2nix, and it generates the variable names of the created nix derivations with the same name as the original name from npm. That means you can have a name like "@foo/bar". When you check the resulting default.nix with nix repl -f default.nix, you don't have a way of calling the generated derivation, since they are quoted.

Describe the solution you'd like
If the repl had a variable, say _scope, with all the variables in the global scope, you could call the above example with _scope."@foo/bar".

Describe alternatives you've considered
There are workarounds, like calling import instead of using -f, but having this additional option would improve usability a bit.

[roberth]

Another workaround:

nix-repl> let "a b" = "cool I guess"; in                          
           { inherit "a b"; }."a b"
"cool I guess"