@function __str-concat($source: '', $args...) {
    @if __is-iteratee-call($args...) {
        $args: nth($args, 1);
    }

    $source: __to-string($source);

    @each $string in $args {
        $source: $source + $string;
    }

    @return $source;
}


@function __concat($source, $args...) {
    $separator: list-separator($source);

    $source: __either($source, ($source,), '__is-list-like');

    @each $list in $args {
        $source: join($source, $list, $separator);
    }

    @return $source;
}

/// Returns a new list comprised of the `$source` list
/// joined with the list(s) and/or value(s) 
/// provided as arguments.
/// 
/// The separator of the returned list will be the same as the
/// separator of the `$source` list.
///
/// @access public
/// @group List
/// @param {List} $source The initial list
/// @param {List...|*...} $args... Lists and/or values to concatenate into the source list. 
/// @returns {List} Returns a new list of concatenated lists/values.
/// @example scss
/// $foo: _concat(1 2, 3 4);
/// // => (1 2 3 4)
/// 
/// $foo: _concat(1 2, 3, 4);
/// // => (1 2 3 4)
@function _concat($args...) {
    @return call(get-function('__concat'), $args...);
}

/// Combines the text of two or more strings and returns a new string.
/// 
/// @access public
/// @group String
/// @param {String} $source [''] - Source string
/// @param {String...|*...} $args... - Other strings to concatenate
/// @returns {String} Returns a new string of concatenated strings
/// @example scss
/// $foo: _concat('Hello', ' ', 'World');
/// // => 'Hello World'
@function _str-concat($args...) {
    @return call(get-function('__str-concat'), $args...);
}