Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.8)
// Compass (v1.0.0.alpha.19)
// ----

// Trying to figure out the best solution 
// to instanciate a comma-separated empty list
// ---
// So far: `zip(())`
// ---

// Arglist version
// ---
// @pro: works in Sass 3.2.19
// ---
// @con: defines `$args` but needs to be called with no arg
// @con: can't be used as a one-liner, without the function
// @con: returns an arglist
// ---
@function comma-list-arglist($args...) {
  @return $args
}

// Join version
// ---
@function comma-list-join() {
  @return join((), (), comma)
}

// Append version
// ---
// @con: add an empty value to list, increasing length from 1
// ---
@function comma-list-append() {
  @return append((), (), comma)
}

// Zip version
// ---
// @pro: is very short
// @pro: works in Sass 3.2.19
// ---
@function comma-list-zip() {
  @return zip(())
}

// Comma version
// ---
// @con: doesn't work in Sass 3.2.19
// @con: add an empty value to list, increasing length from 1
// ---
@function comma-list-trailing-comma() {
  @return (),
}

// Describe test
// ---
@mixin test($function) {
  // Instanciate new list
  $new-list: if($function == "regular-list", (), call($function));
  $list: $new-list;
  
  // Fill
  $list: append($list, alpha);
  $list: append($list, beta);
  $list: append($list, gamma);
  
  // Dump data
  method: unquote($function);
  output: $list;
  length: length($list);
  type-when-empty: type-of($new-list);
  type-when-full: type-of($list);
  separator: list-separator($list);
  /**/
}

// Run test
// ---
regular-list {
  @include test("regular-list");
  @include test("comma-list-zip");
  @include test("comma-list-join");
  @include test("comma-list-arglist");
  @include test("comma-list-append");
  @include test("comma-list-trailing-comma");
}

SassMeister-output.css

regular-list {
  method: regular-list;
  output: alpha beta gamma;
  length: 3;
  type-when-empty: list;
  type-when-full: list;
  separator: space;
  /**/
  method: comma-list-zip;
  output: alpha, beta, gamma;
  length: 3;
  type-when-empty: list;
  type-when-full: list;
  separator: comma;
  /**/
  method: comma-list-join;
  output: alpha, beta, gamma;
  length: 3;
  type-when-empty: list;
  type-when-full: list;
  separator: comma;
  /**/
  method: comma-list-arglist;
  output: alpha, beta, gamma;
  length: 3;
  type-when-empty: arglist;
  type-when-full: list;
  separator: comma;
  /**/
  method: comma-list-append;
  output: alpha, beta, gamma;
  length: 4;
  type-when-empty: list;
  type-when-full: list;
  separator: comma;
  /**/
  method: comma-list-trailing-comma;
  output: alpha, beta, gamma;
  length: 4;
  type-when-empty: list;
  type-when-full: list;
  separator: comma;
  /**/
}