In #89 it has been reported that the third step can't be done as
`nix-repl` doesn't evaluate anymore on 18.09 and unstable as in both
cases an evaluation error will be thrown.
First of all this may confuse new users who want to learn Nix, but don't
know the ecosystem sufficiently to understand why the install failed.
As recent NixOS versions (unstable and 18.09) use Nix 2.0 by default and
unstable doesn't evaluate with Nix 1.x anymore it should be a safe thing
to do now.
This patch covers two aspects:
* Using Nix 2.0: I replayed the installation steps with `nix-env` to
ensure that the steps and explanations provided in the first three
chapters are still valid.
* Replacing `nix-repl` references: most of the cases it was sufficient
to replace `nix-repl` with the newly introduced command `nix repl`.
In chapter three `nix-repl` was used to demonstrate the installation
of a package with `nix-env`. I decided to use `nix-index` as demo
package as I figured this tool to be extremely helpful to locate
packages by output files.
The explanation that Nix is not only a tool for package/derivation
management, but a functional language as well was moved to chapter
four where the basics of the language were actually covered.
This change is just a first step towards an updated series, in the
future we may want to use even more Nix 2.0 features (such as
`nix-build` vs. `nix build` with `nix log`).
Fixes#89
Possibly supersedes #71
+ refer to the old nixpkgs commit in a note but use the current nixpkgs for the
actual examples
+ add which to the PATH
+ add `unpackPhase = "true";` to satisfy stdenv requirements
+ explain how _PATH and PATH are related
+ add a few missing words
+ pick the lowercase spelling for `stdenv` and use it consistenly
+ reword a sentence that I had a hard time understanding
+ fix the path of the second nix expression to be included
It's not immediately obvious which previous `mul` definition applies,
and is a copy-paste hazard. Staring the block with a `mul = ...` is also
consistent with the other code blocks.
Fixes#46
