$imported-modules: () !default;

/// Module export mixin
/// This mixin helps making sure a module is imported once and only once.
/// @access public
/// @param {String} $name - Name of exported module
/// @param {Bool} $warn [false] - Warn when module has been already imported
/// @require $imported-modules
@mixin exports($name, $warn: false) {
    @if (index($imported-modules, $name) == null) {
        $imported-modules: append($imported-modules, $name) !global;
        @content;
    } @else if $warn == true {
        @warn "Module `#{$name}` has already been imported.";
    }
}