public static function buildExpressions(array $expressions)
    {
        foreach ($expressions as $k => $expr) {
            if ($expr instanceof self) {
                $if = $expr->ifPart;
                $then = $expr->thenPart;
                $expressions[$k] = function ($v) use ($if, $then) {
                    return $if($v) ? $then($v) : $v;
                };
            }
        }

        return $expressions;
    }