Laravel Elixir + PostCSS + Sass (or Stylus or Less or other preprocessor)

gulpfile.js

// Task to compile styles with PostCSS
elixir.extend('processStyles', options=> {
	var name = 'processStyles'
	var sourcemaps = require('gulp-sourcemaps')
	var err = e => {
		console.log(require('gulp-util').colors.bgRed('PostCSS - Error'))
		console.log(e.message)
	}
	var notification = require('laravel-elixir/Notification')
	new elixir.Task(name, ()=> {
		return gulp.src(options.src, {cwd: config.assetsPath})
			.pipe(gulpif(config.sourcemaps, sourcemaps.init()))
			.pipe(require('gulp-sass')().on('error', err))
			.pipe(require('gulp-postcss')(
				[
					require('postcss-devtools'),
					require('autoprefixer'),
					require('postcss-axis'),
					require('postcss-short'),
					require('postcss-import')
				]
			).on('error', err))
			.pipe(gulpif(config.sourcemaps, sourcemaps.write('.')))
			.pipe(gulp.dest(`${config.publicPath}/${config.css.outputFolder}`))
			.pipe(new notification().message(name + ' Compiled!'))
	})
	.watch(config.assetsPath + '/' + options.watch)
	.ignore(config.css.outputFolder + '/**/*.css') // not sure about this
})
elixir(mix=> {
	mix.processStyles({
		src: [
			'!sass/_*',
			'sass/*.{scss,sass}'
		],
		watch: 'sass/**/*.{scss,sass}'
	})
})