@function __function-exists($function, $args...) {
    @if type-of($function) != 'string' {
        @return false;
    }

    @if index(('e', 'pi'), $function) {
        @return false;
    }

    @return if(function-exists($function),
        true,
        function-exists(__function-name($function))
    );
}


@function __function-scope($function) {
    @if type-of($function) != 'string' {
        @return null;
    }

    $scope-index: str-index($function, '@');
    $scope-id: false;

    @if $scope-index {
        $scope-id: str-slice($function, $scope-index);
    }

    @return $scope-id;
}


@function __function-name($function) {
    @if type-of($function) != 'string' {
        @return null;
    }

    $scope-index: str-index($function, '@');

    @return if($scope-index, str-slice($function, 1, $scope-index - 1), $function);
}


@function __call($method, $this-arg: $__current-scope__, $args...) {
    $function-name: __function-name($method);
    $scope-id: __function-scope($method);
    $previous-scope: $__current-scope__;
    $scope-id: if($scope-id, $scope-id, $this-arg);

    @if $scope-id {
        $__current-scope__: $scope-id !global;
    }

    $method-name: __this($function-name);

    @if $method-name != null and __function-exists(__this($function-name)) {
        $function-name: __this($function-name);
    } @else if not ($function-name and __function-exists($function-name)) {
        $__current-scope__: $previous-scope !global;
        
        @error 'Function #{$function-name} does not exist.';
        @return null;
    }

    $result: call(get-function($function-name), $args...);
    $__current-scope__: $previous-scope !global;

    @return $result;
}


@function _call($args...) {
    @return call(get_function(__call), $args...);
}