pkgs:

rec {


  runLaTeX =
    { rootFile
    , generatePDF ? true # generate PDF, not DVI
    , generatePS ? false # generate PS in addition to DVI
    , extraFiles ? []
    , compressBlanksInIndex ? true
    , packages ? []
    , texPackages ? {}
    , copySources ? false
    }:

    assert generatePDF -> !generatePS;

    let
      tex = pkgs.texlive.combine
        # always include basic stuff you need for LaTeX
        ({inherit (pkgs.texlive) scheme-basic;} // texPackages);
    in

    pkgs.stdenv.mkDerivation {
      name = "doc";

      builder = ./run-latex.sh;
      copyIncludes = ./copy-includes.pl;

      inherit rootFile generatePDF generatePS extraFiles
        compressBlanksInIndex copySources;

      includes = map (x: [x.key (baseNameOf (toString x.key))])
        (findLaTeXIncludes {inherit rootFile;});

      buildInputs = [ tex pkgs.perl ] ++ packages;
    };


  # Returns the closure of the "dependencies" of a LaTeX source file.
  # Dependencies are other LaTeX source files (e.g. included using
  # \input{}), images (e.g. \includegraphics{}), bibliographies, and
  # so on.
  findLaTeXIncludes =
    { rootFile
    }:

    builtins.genericClosure {
      startSet = [{key = rootFile;}];

      operator =
        {key, ...}:

        let

          # `find-includes.pl' returns the dependencies of the current
          # source file (`key') as a list, e.g. [{type = "tex"; name =
          # "introduction.tex";} {type = "img"; name = "example"}].
          # The type denotes the kind of dependency, which determines
          # what extensions we use to look for it.
          deps = import (pkgs.runCommand "latex-includes"
            { rootFile = baseNameOf (toString rootFile); src = key; }
            "${pkgs.perl}/bin/perl ${./find-includes.pl}");

          # Look for the dependencies of `key', trying various
          # extensions determined by the type of each dependency.
          # TODO: support a search path.
          foundDeps = dep: xs:
            let
              exts =
                if dep.type == "img" then [".pdf" ".png" ".ps" ".jpg"]
                else if dep.type == "tex" then [".tex" ""]
                else [""];
              fn = pkgs.lib.findFirst (fn: builtins.pathExists fn) null
                (map (ext: dirOf key + ("/" + dep.name + ext)) exts);
            in if fn != null then [{key = fn;}] ++ xs
               else xs;

        in pkgs.lib.foldr foundDeps [] deps;
    };


  findLhs2TeXIncludes =
    { lib
    , rootFile
    }:

    builtins.genericClosure {
      startSet = [{key = rootFile;}];

      operator =
        {key, ...}:

        let

          deps = import (pkgs.runCommand "lhs2tex-includes"
            { src = key; }
            "${pkgs.stdenv.bash}/bin/bash ${./find-lhs2tex-includes.sh}");

        in pkgs.lib.concatMap (x: lib.optionals (builtins.pathExists x) [{key = x;}])
                              (map (x: dirOf key + ("/" + x)) deps);
    };

  dot2pdf =
    { dotGraph
    }:

    pkgs.stdenv.mkDerivation {
      name = "pdf";
      builder = ./dot2pdf.sh;
      inherit dotGraph fontsConf;
      buildInputs = [
        pkgs.perl pkgs.graphviz
      ];
    };


  dot2ps =
    { dotGraph
    }:

    pkgs.stdenv.mkDerivation {
      name = "ps";
      builder = ./dot2ps.sh;
      inherit dotGraph;
      buildInputs = [
        pkgs.perl pkgs.graphviz pkgs.ghostscript
      ];
    };

  lhs2tex =
    { source, flags ? null } :
    pkgs.stdenv.mkDerivation {
      name = "tex";
      builder = ./lhs2tex.sh;
      inherit source flags;
      buildInputs = [ pkgs.lhs2tex pkgs.perl ];
      copyIncludes = ./copy-includes.pl;
      includes = map (x: [x.key (baseNameOf (toString x.key))])
        (findLhs2TeXIncludes {rootFile = source;});
    };

  animateDot = dotGraph: nrFrames: pkgs.stdenv.mkDerivation {
    name = "dot-frames";
    builder = ./animatedot.sh;
    inherit dotGraph nrFrames;
  };


  # Wrap a piece of TeX code in a document.  Useful when generating
  # inline images from TeX code.
  wrapSimpleTeX =
    { preamble ? null
    , body
    , name ? baseNameOf (toString body)
    }:

    pkgs.stdenv.mkDerivation {
      inherit name preamble body;
      buildCommand = ''
        touch $out
        echo '\documentclass{article}' >> $out
        echo '\pagestyle{empty}' >> $out
        if test -n "$preamble"; then cat $preamble >> $out; fi
        echo '\begin{document}' >> $out
        cat $body >> $out
        echo '\end{document}' >> $out
      '';
    };


  # Convert a Postscript file to a PNG image, trimming it so that
  # there is no unnecessary surrounding whitespace.
  postscriptToPNG =
    { postscript
    }:

    pkgs.stdenv.mkDerivation {
      name = "png";
      inherit postscript;

      buildInputs = [pkgs.imagemagick pkgs.ghostscript];

      buildCommand = ''
        if test -d $postscript; then
          input=$(ls $postscript/*.ps)
        else
          input=$(stripHash $postscript)
          ln -s $postscript $input
        fi

        mkdir -p $out
        convert -units PixelsPerInch \
          -density 600 \
          -trim \
          -matte \
          -transparent '#ffffff' \
          -type PaletteMatte \
          +repage \
          $input \
          "$out/$(basename $input .ps).png"
      ''; # */
    };


  # Convert a piece of TeX code to a PNG image.
  simpleTeXToPNG =
    { preamble ? null
    , body
    , packages ? []
    }:

    postscriptToPNG {
      postscript = runLaTeX {
        rootFile = wrapSimpleTeX {
          inherit body preamble;
        };
        inherit packages;
        generatePDF = false;
        generatePS = true;
      };
    };


  # Convert a piece of TeX code to a PDF.
  simpleTeXToPDF =
    { preamble ? null
    , body
    , packages ? []
    }:

    runLaTeX {
      rootFile = wrapSimpleTeX {
        inherit body preamble;
      };
      inherit packages;
    };


  # Some tools (like dot) need a fontconfig configuration file.
  # This should be extended to allow the called to add additional
  # fonts.
  fontsConf = pkgs.makeFontsConf {
    fontDirectories = [
      "${pkgs.ghostscript.fonts}/share/fonts"
    ];
  };

}
