无痛支持所有 Java 的 控制流语句，除了 switch 语句。
if (doc[item].size() == 0) {
// do something if "item" is missing
} else if (doc[item].value == 'something') {
// do something if "item" value is: something
} else {
// do something else
}
无痛还支持 for in 语法
for (def item : list) {
// do something
}
for (item in list) {
// do something
}
while (ctx._source.item < condition) {
// do something
}
do {
// do something
}
while (ctx._source.item < condition)