Switch to using Nix flakes (#253)

Someone has requested me to build this book, since they didn't have Nix.

So when looking at the Nix expressions I found that there was only a
shell.nix and the default.nix was essentially just aliasing the
shell.nix but without the pinning.

However, with Nix flakes we no longer need to do pinning like this and
we instead have a flake.lock file, which essentially pins the
corresponding revisions.

I also added a default.nix, which uses flake-compat to make sure that
nix-shell and nix-build work as before.

Since so far the way to build the PDF(s) was to get into a Nix shell and
run make accordingly. For me however it's unacceptable to build random
code without the Nix sandbox, so while writing a proper default.nix I
decided it would be better to turn it into a Nix flake.

Apart from the previous ways to build this project we now have:

  $ nix develop # To get a Nix shell (similar to nix-shell but cached)
  $ nix build # The default edition
  $ nix build .\#ctfp-scala # The Scala edition
  $ nix build .\#ctfp-ocaml # The OCaml edition

Signed-off-by: aszlig <aszlig@nix.build>

Author: aszlig

default.nix

@@ -1,5 +1,6 @@
-# nix-shell --pure --command 'cd src; make'
 let
-  nixpkgs = import <nixpkgs> {};
-in
-  nixpkgs.callPackage ./shell.nix {}
+  rev = "cecfd08d13ddef8a79f277e67b8084bd9afa1586";
+  url = "https://github.com/edolstra/flake-compat/archive/${rev}.tar.gz";
+  flake = import (fetchTarball url) { src = ./.; };
+  inNixShell = builtins.getEnv "IN_NIX_SHELL" != "";
+in if inNixShell then flake.shellNix else flake.defaultNix

flake.lock

@@ -0,0 +1,139 @@
+{
+  description = "Category Theory for Programmers";
+
+  inputs.nixpkgs.url = "nixpkgs/nixos-20.03";
+  inputs.utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, utils }: utils.lib.eachDefaultSystem (system: let
+    pkgs = nixpkgs.legacyPackages.${system};
+    inherit (nixpkgs) lib;
+
+    ###########################################################################
+    # LaTeX Environment
+    texliveEnv = pkgs.texlive.combine {
+      inherit (pkgs.texlive)
+        bookcover
+        textpos
+        fgruler
+        tcolorbox
+        fvextra
+        framed
+        newtx
+        nowidow
+        emptypage
+        wrapfig
+        subfigure
+        adjustbox
+        collectbox
+        tikz-cd
+        imakeidx
+        idxlayout
+        titlesec
+        subfiles
+        lettrine
+        upquote
+        libertine
+        mweights
+        fontaxes
+        mdframed
+        needspace
+        xifthen
+        ifnextok
+        currfile
+        noindentafter
+        ifmtarg
+        scheme-medium
+        listings
+        minted
+        microtype
+        babel
+        todonotes
+        chngcntr
+        ifplatform
+        xstring
+        minifp
+        titlecaps
+        enumitem
+        environ
+        trimspaces
+        l3packages
+        zref
+        catchfile
+        import
+        ;
+    };
+
+    ###########################################################################
+    # Python Environment
+
+    # Pin the Python version and its associated package set in a single place.
+    python = pkgs.python38;
+    pythonPkgs = pkgs.python38Packages;
+
+    pygments-style-github = pythonPkgs.buildPythonPackage rec {
+      pname = "pygments-style-github";
+      version = "0.4";
+
+      doCheck = false; # Hopefully someone else has run the tests.
+
+      src = pythonPkgs.fetchPypi {
+        inherit pname version;
+        sha256 = "19zl8l5fyb8z3j8pdlm0zbgag669af66f8gn81ichm3x2hivvjhg";
+      };
+
+      # Anything depending on this derivation is probably also gonna want
+      # pygments to be available.
+      propagatedBuildInputs = with pythonPkgs; [ pygments ];
+    };
+
+    pythonEnv = python.withPackages (
+      pyPkgs: with pyPkgs; [
+        pygments
+        pygments-style-github
+      ]
+    );
+
+    mkPackageName = edition:
+      "ctfp${lib.optionalString (edition != null) "-${edition}"}";
+
+    mkPackage = isShell: edition: pkgs.stdenv.mkDerivation {
+      name = mkPackageName edition;
+      src = if isShell then null else self;
+
+      makeFlags = [
+        "-C" "src" "OUTPUT_DIR=$(out)"
+        "GIT_VER=${self.rev or self.lastModifiedDate}"
+      ];
+
+      buildFlags = lib.optional (edition != null) edition;
+
+      dontInstall = true;
+
+      FONTCONFIG_FILE = pkgs.makeFontsConf {
+        fontDirectories = with pkgs; [ inconsolata-lgc libertine libertinus ];
+      };
+
+      buildInputs = with pkgs; [
+        # Misc. build tooling.
+        gnumake
+        git
+        python3Packages.virtualenv
+        which
+        # LaTeX Environment (with all associated libraries and packages).
+        texliveEnv
+        # Python Environment (with all associated libraries and packages).
+        pythonEnv
+      ];
+    };
+
+    editions = [ null "scala" "ocaml" ];
+
+  in {
+    packages = lib.listToAttrs (map (edition: {
+      name = mkPackageName edition;
+      value = mkPackage false edition;
+    }) editions);
+    defaultPackage = self.packages.${system}.ctfp;
+    devShell = mkPackage true null;
+  });
+}

flake.nix

@@ -5,6 +5,7 @@
 
 DIR := $(shell pwd)
 GIT_VER := $(shell git describe --tags --always --long | tr -d '\n')
+OUTPUT_DIR := ../out/$(GIT_VER)
 
 OUTPUT = category-theory-for-programmers
 
@@ -54,7 +55,7 @@ $(TOPPDFFILES) : %.pdf : %.tex $(TEXFILES)
 	if which latexmk > /dev/null 2>&1 ;\
 	then \
 		latexmk -shell-escape -interaction=nonstopmode -halt-on-error -norc -jobname=ctfp -pdflatex="xelatex %O %S" -pdf $< ;\
-		mv ctfp.pdf ../out/$(GIT_VER)/$(subst ctfp,$(OUTPUT),$(subst ctfp-reader,$(OUTPUT),$*)).pdf ;\
+		mv ctfp.pdf $(OUTPUT_DIR)/$(subst ctfp,$(OUTPUT),$(subst ctfp-reader,$(OUTPUT),$*)).pdf ;\
 	else @printf "Error: unable to find latexmk. Is it installed?\n" ;\
 	fi
 
@@ -64,8 +65,8 @@ version.tex:
 	@printf '}' >> version.tex
 
 out-dir:
-	@printf 'Creating output directory: $(GIT_VER)\n'
-	mkdir -p ../out/$(GIT_VER)
+	@printf 'Creating output directory: $(OUTPUT_DIR)\n'
+	mkdir -p $(OUTPUT_DIR)
 
 clean:
 	rm -f *~ *.aux {ctfp-*}.{out,log,pdf,dvi,fls,fdb_latexmk,aux,brf,bbl,idx,ilg,ind,toc,sed}