@function __partition-initializer() {
    @return ((), ());
}


@function __partition-aggregator($result, $value, $key, $args...) {
    $result-index: if(__is-truthy($key), 1, 2);
    $result-value: nth($result, $result-index);
    $result-value: if($result-value, $result-value, ());

    @return set-nth($result, $result-index, append($result-value, $value));
}


@function __partition($arguments...) {
    $function: __create-aggregator('__partition-aggregator', '__partition-initializer');

    @return __exec($function, $arguments...);
}


/// Creates a list of elements split into two groups, the first of which
/// contains elements `$predicate` returns truthy for, while the second of which
/// contains elements `$predicate` returns falsey for.
/// 
/// The predicate is bound
/// to `$this-arg` and invoked with three arguments; (value, index|key, collection).
/// 
/// If a property name is provided for `$predicate` the created `_property`
/// style callback returns the property value of the given element.
/// If a value is also provided for `$this-arg` the created `_matches-property`
/// style callback returns `true` for elements that have a matching property
/// value, else `false`.
/// 
/// If a map is provided for `$predicate` the created `_matches` style
/// callback returns `true` for elements that have the properties of the given
/// object, else `false`.
///
///
/// @access public
/// @group Collection
/// @param {List|Map|string} $collection The collection to iterate over.
/// @param {Function|Map|string} $predicate [_identity] - The function invoked
///  per iteration.
/// @param {*} $this-arg [null] - The `_this` binding of `$predicate`.
/// @returns {List} Returns the list of grouped elements.
/// @example scss
/// $foo: _partition(1.3 1.4 2.1 2.2, floor);
/// // => ((1.3 1.4), (2.1 2.2))

@function _partition($args...) {
    @return call(get-function('__partition'), $args...);
}