gistfile1.js

function copy(o) {
  var p = {};
  for (var k in o)
    p[k] = o[k];
  return p;
}

function Mapper(source) {
  this.source = source;
  this.result = {};
}

Mapper.prototype.walk = function(keys, key) {
  var source_curr = this.source;
  var result_curr = this.result;
  keys = keys.concat([key]);
  for (var i = 0; i < keys.length; i++) {
    source_curr = source_curr[keys[i]];
    result_curr[keys[i]] = {};
    result_curr = result_curr[keys[i]];
  }
  this.source_curr = source_curr;
  this.result_curr = result_curr;
  return keys;
};

Mapper.prototype.refer = function(keys, key_src, key_dest) {
  if (key_dest === undefined)
    key_dest = key_src;
  this.result_curr[key_dest] = copy(this.source_curr[key_src]);
  this.source_curr = this.source_curr[key_src];
  this.result_curr = this.result_curr[key_dest];
};

Mapper.prototype.transfer = function(key, val_or_fn) {
  this.result_curr[key] = typeof val_or_fn === "function" ?
      val_or_fn(this.source_curr[key])
    : val_or_fn;
};

function add_suffix(path_str, suffix) {
  var parts = path.parse(path_str);
  var name = parts.name;
  var i = name.indexOf(".");
  if (i !== -1)
    name = name.slice(0, i) + suffix + name.slice(i);
  else
    name += suffix;
  var new_path = path.format({
    dir: parts.dir,
    base: name+parts.ext
  });
  return new_path;
}

var add_noprint_suffix = function(path_str) {
  return add_suffix(path_str, "-noprint");
};

function() {
  var child1, child2, child3, root = [];
  var mapper = new Mapper(config);
  child1 = mapper.walk(root, "less");
  child2 = mapper.refer(child1, "compileCore", "compileNoPrint");
  mapper.transfer("src", add_noprint_suffix);
  mapper.transfer("dest", add_noprint_suffix);
  child3 = mapper.refer(child2, "options");
  mapper.transfer("sourceMapURL", add_noprint_suffix);
  mapper.transfer("sourceMapFilename", add_noprint_suffix);

  child1 = mapper.walk(root, "autoprefixer");
  child2 = mapper.refer(child1, "core", "noPrint");
  mapper.transfer("src", add_noprint_suffix);

  child1 = mapper.walk(root, "cssmin");
  child2 = mapper.refer(child1, "minifyCore", "minifyNoPrint");
  mapper.transfer("src", add_noprint_suffix);
  mapper.transfer("dest", add_noprint_suffix);

  child1 = mapper.walk(root, "csscomb");
  child2 = mapper.refer(child1, "dist", "noPrint");
  mapper.transfer("src", "*-noprint.css");

  grunt.config.merge(mapper.result);
}

gistfile2.js

var lenses = require("lenses"),
    compose = require('pointfree-fantasy').compose;

function add_suffix(path_str, suffix) {
  var parts = path.parse(path_str);
  var name = parts.name;
  var i = name.indexOf(".");
  if (i !== -1)
    name = name.slice(0, i) + suffix + name.slice(i);
  else
    name += suffix;
  var new_path = path.format({
    dir: parts.dir,
    base: name+parts.ext
  });
  return new_path;
}

var add_noprint_suffix = function(path_str) {
  return add_suffix(path_str, "-noprint");
};

function over2(lens, src, key_src, key_dest, cb) {
  return function(dest) {
    var obj = {};
    obj[key_dest] = cb(lenses.view(lens, src)[key_src]);
    return lenses.set(lens, obj, dest);
  };
}

function() {
  var Lenses1 = lenses.makeLenses(["less", "autoprefixer", "cssmin", "csscomb"]);
  var Lenses2 = lenses.makeLenses(["src", "dest", "options"]);
  var Lenses_less_options = lenses.makeLenses(["sourceMapURL", "sourceMapFilename"]);
  var config = grunt.config.get();
  var transform = compose(
    over2(Lenses1.less, config, "compileCore", "compileNoPrint",
      compose(lenses.set(Lenses2.src, "less/bootstrap-noprint.less"),
              lenses.over(Lenses2.dest, add_noprint_suffix),
              lenses.over(Lenses2.options,
                compose(lenses.over(Lenses_less_options.sourceMapURL, add_noprint_suffix),
                        lenses.over(Lenses_less_options.sourceMapFilename, add_noprint_suffix))))),
    over2(Lenses1.autoprefixer, config, "core", "noPrint",
      lenses.over(Lenses2.src, add_noprint_suffix)),
    over2(Lenses1.cssmin, config, "minifyCore", "minifyNoPrint",
      compose(lenses.over(Lenses2.src, add_noprint_suffix),
              lenses.over(Lenses2.dest, add_noprint_suffix))),
    over2(Lenses1.csscomb, config, "dist", "noPrint",
      lenses.set(Lenses2.src, "*-noprint.css")));
  var additional_config = {
    copy: {
      noPrintLess: {
        src: "less/bootstrap.less",
        dest: "less/bootstrap-noprint.less",
        options: {
          process: function(content, srcpath) {
            return content.replace('@import "print.less"', "");
          }
        }
      },
      noPrintDist: {
        src: "dist/css/bootstrap-noprint.*",
        dest: dir_dest
      }
    }
  };
  additional_config = transform(additional_config);
  grunt.config.merge(additional_config);
}