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SassMeister-input.scss

// ----
// Sass (v3.4.9)
// Compass (v1.0.1)
// ----

////
// Iterators in Sass, just for the heck of it.
// @access public
// @see https://github.com/HugoGiraudel/SassyIterators
// @see http://sassmeister.com/gist/d94049a3d516e31a8dad Demo
////

/// Iterator initialization
/// @param {List | Map | String} $collection
/// @param {String | Null} $mapping
/// @param {Arglist} $mapping-args - Extra arguments for `$mapping`
/// @return {Iterator}
@function iterator($collection, $mapping: null, $mapping-args...) {
  @return (
    'collection': $collection,
    'position': 0,
    'mapping': $mapping,
    'mapping-args': $mapping-args,
    'value': null,
    'done': false
  );
}

/// Iterator reset
/// @param {Iterator} $iterator
/// @return {Iterator}
/// @require iterator
@function iterator-rewind($iterator) {
  @return iterator(map-get($iterator, 'collection'));
}

/// Iterator validity checker
/// @param {Iterator} $iterator
/// @return {Boolean}
@function iterator-valid($iterator) {
  @return map-get($iterator, 'done') == false;
}

/// Iterator next
/// @param {Iterator} $iterator
/// @return {Iterator}
@function iterator-next($iterator) {
  $collection: map-get($iterator, 'collection');
  $position: map-get($iterator, 'position') + 1;
  $value: map-get($iterator, 'value');
  $mapping: map-get($iterator, 'mapping');
  $done: map-get($iterator, 'done');
  $mapping-args: map-get($iterator, 'mapping-args');

  @if type-of($collection) == 'string' {
    $done: $position > str-length($collection);
    $value: if($done, null, str-slice($collection, $position, $position));
  } @else if type-of($collection) == 'list' {
    $done: $position > length($collection);
    $value: if($done, null, nth($collection, $position));
  } @else if type-of($collection) == 'map' {
    $done: $position > length($collection);
    $value: if($done, null, nth(map-keys($collection), $position) map-get($collection, nth(map-keys($collection), $position)));
  } @else {
    @warn "Unsupported collection type: #{type-of($collection)}.";
  }

  @return map-merge($iterator, (
    'done': $done,
    'value': if($done == false and $mapping, call($mapping, $value, $mapping-args...), $value),
    'position': $position
  ));
}

/// Iterator API cleaner
/// @param {Iterator} $iterator
/// @return {Simple Iterator}
@function iterator-api($iterator) {
  @return (
    'done': map-get($iterator, 'done'),
    'value': map-get($iterator, 'value')
  );
}

// Iterator tester
@mixin iterator-test($collection, $mapping: null, $mapping-args...) {
  // Initialize a new iterator
  $iterator: iterator($collection, $mapping, $mapping-args...);

  // Iterate over it, while it's not done
  @while iterator-valid($iterator) {
    // Inspect the (cleaned) iterator
    content: inspect(iterator-api($iterator));

    // Get next value from iterator
    $iterator: iterator-next($iterator);
  }

  // Inspect it one last time to see it finished
  content: inspect(iterator-api($iterator));
}

.test-string {
  @include iterator-test("Hello!");
}

.test-list {
  @include iterator-test('a' 'b' 'c' 'd', 'to-upper-case');
}

.test-map {
  @include iterator-test(('a': 1, 'b': 2));
}

SassMeister-output.css

.test-string {
  content: ("done": false, "value": null);
  content: ("done": false, "value": "H");
  content: ("done": false, "value": "e");
  content: ("done": false, "value": "l");
  content: ("done": false, "value": "l");
  content: ("done": false, "value": "o");
  content: ("done": false, "value": "!");
  content: ("done": true, "value": null);
}

.test-list {
  content: ("done": false, "value": null);
  content: ("done": false, "value": "A");
  content: ("done": false, "value": "B");
  content: ("done": false, "value": "C");
  content: ("done": false, "value": "D");
  content: ("done": true, "value": null);
}

.test-map {
  content: ("done": false, "value": null);
  content: ("done": false, "value": "a" 1);
  content: ("done": false, "value": "b" 2);
  content: ("done": true, "value": null);
}