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nix-mode and nix-shell - Major mode for nix expressions and integration of Emacs to nix-shell with nix-shell

Author: Mario Rodas marsam@users.noreply.github.com
Version: 0.1

A major mode for Nix expressions.

Usage of nix-shell (this section added by @analyticd)

In the case of Python, it seems that direnv integration (direnv from Nix, direnv Emacs package, .envrc containing 'use nix' in your nix-shell directory, and 'direnv allow .' in same) to Emacs is needed in addition to nix-shell.el in Emacs. With just direnv integration to Emacs, the shell is built, but Emacs must be launched from within the nix-shell on the command line in order to use the appropriate python executable. With nix-shell.el, you can do M-x nix-shell-activate (in concert with the aforementioned coordination of direnv) and Emacs will pick up the nix-shell environment including the path to the python exectable (and other necessary config) defined (and implied) by the shell.nix file.

Bottom line: Mario has solved the problem of getting Emacs to use nix-shell executables in Emacs without having to start Emacs from within a nix-shell.

    (use-package nix-mode
      :load-path (lambda () (expand-file-name "github.com/analyticd/nix-mode" ghq-root))) ; just the path to the repo will do

    ;; M-x nix-shell-active will look for your default.nix or shell.nix
    ;; and make sure to find the proper nix-shell-based executables. Works
    ;; great for Python for instance. No more need for direnv integration
    ;; with Emacs (which is very slow).
    (use-package nix-shell
      :load-path (lambda () (expand-file-name "github.com/analyticd/nix-mode" ghq-root)))

Here is an example shell.nix for Python use (in my case using a tarball from the stable channel to ensure that binaries and not source are used - no compiling please, this is Nix after all - I'm looking at you pandas on unstable channel):

    {
      pkgs ? import (fetchTarball {
        url = https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.09.tar.gz;
        # sha256 = "0xvj0z928mzcs56hindxw608a6jm1fvsi2ap5r7m4a0plnrcwx90";
      }) {}
    }:
    pkgs.mkShell {
      buildInputs = with pkgs; [
        python3Full
        python3Packages.pip
        python3Packages.numpy
        python3Packages.pandas
        python3Packages.matplotlib
        python3Packages.pyyaml
        python3Packages.scipy
        python3Packages.pillow
        python3Packages.pymongo
      ];
      shellHook = ''
      # echo 'Entering Python Project Environment'
      # set -v

      # If you want to use pip:
      # extra packages can be installed here
      unset SOURCE_DATE_EPOCH
      export PIP_PREFIX="$(pwd)/_build/pip_packages"
      python_path=(
        "$PIP_PREFIX/lib/python3/site-packages"
        "$PYTHONPATH"
      )
      # use double single quotes to escape bash quoting
      IFS=: eval 'python_path="''${python_path[*]}"'
      export PYTHONPATH="$python_path"
      # export MPLBACKEND='Qt4Agg'  # Put this in ~/.matplotlib/matplotlibrc instead. On OS X, use 'backend: MacOS'

      # set +v
      '';
    }

Here is an example shell.nix for multiple language use (Python, Haskell) in, say, an org-babel environment for executing org source blocks (placed in your org-directory):

    {
      pkgs ? import (fetchTarball {
        url = https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.09.tar.gz;
        # sha256 = "0xvj0z928mzcs56hindxw608a6jm1fvsi2ap5r7m4a0plnrcwx90";
      }) {}
    }:
    pkgs.mkShell {
      buildInputs = with pkgs; [
        python3Full
        python3Packages.pip
        python3Packages.numpy
        python3Packages.pandas
        python3Packages.matplotlib
        python3Packages.pyyaml
        python3Packages.scipy
        julia_11
        # python3Packages.pillow
        # python3Packages.pymongo
        (ghc.withPackages (p: [
          p.lens p.aeson p.lens-aeson p.text p.vector p.hmatrix
        ]))
      ];
      shellHook = ''
      # eval "$(direnv hook zsh)"  # Put this in my .zshrc
      # direnv allow .

      # echo 'Entering Python Project Environment'
      # set -v

      # extra packages can be installed here
      unset SOURCE_DATE_EPOCH
      export PIP_PREFIX="$(pwd)/../../../src/pip_packages"
      python_path=(
        "$PIP_PREFIX/lib/python3/site-packages"
        "$PYTHONPATH"
      )
      # use double single quotes to escape bash quoting
      IFS=: eval 'python_path="''${python_path[*]}"'
      export PYTHONPATH="$python_path"

      set +v
      '';
    }

TODO

Converted from nix-mode.el by el2markdown.