The SignupScript for ZVMS.

• must <expr> return false if <expr> is false, otherwise continue
• just <expr> return true if <expr> is true, otherwise continue
• return <expr> return <expr> and stop
• assignment: <id> = <expr> e.g. new = before & 202203
• comment: # <comment>

If the program reaches the end, it implicitly executes return true.

by priority

1. union: &, | e.g. 202203 | 202204 -> {20220301, 20220302, ..., 20220401, 20220402, ...} e.g. before & 202203 -> (maybe){20220320, 20220321}
2. in operator. In fact it is & with smaller priority. e.g. before in 202203|202204
3. algebra: +, -
4. comparison: ==, !=, >, >=, <, <=
5. logic: !, &&, ||

• union (of student)
• int
• boolean

• [0,2000]: number itself
• (2000,10000): grade id
• [100000,1000000): class id
• [10000000,1000000000): student id
• otherwise: invalid

• any id is always converted to union e.g. 202203 -> {20220301, 20220302, ... } e.g. 20220320 -> {20220320}
• union is converted to int by its size when doing algebra e.g. 202203 + 1->46 e.g. 10 - before->3
• int is converted to boolean by whether it greater than zero e.g. -3->false e.g. 0->false e.g. 3->true

• before: union of students who has signed up e.g. {20220101, 20220202}
• new: student who wants to sign up e.g. 20220303
• after: union of students who has signed up after the new student signs up definition: final = initial | delta e.g. {20220101, 20220202, 20220303}

true or false, indicating whether the student can sign up

See example.signup.

• must <expr> 如果 <expr> 为 false,则返回 false,否则继续执行
• just <expr> 如果 <expr> 为 true,则返回 true,否则继续执行
• return <expr> 返回 <expr> 并停止执行
• 赋值语句:<id> = <expr> 例如:new = before & 202203
• 注释:# <comment>

按优先级排序

1. 集合运算:&、| 例如:202203 | 202204 -> {20220301、20220302、...、20220401、20220402、...} 例如:before & 202203 -> (可能是){20220320、20220321}
2. in 运算符。实际上就是&,但优先级更低 例如:before in 202203|202204
3. 代数运算:+、-
4. 比较运算:==、!=、>、>=、<、<=
5. 逻辑运算:!、&&、||

• 集合(学生的集合)
• 整数
• 布尔值

• [0,2000]:数字本身
• (2000,10000):年级 ID
• [100000,1000000):班级 ID
• [10000000,1000000000):学生 ID
• 其他:无效

• 任何 ID 都会被转换为集合 例如:202203 -> {20220301、20220302、...} 例如:20220320 -> {20220320}
• 集合在进行代数运算时会根据其大小转换为整数 例如:202203 + 1 -> 46 例如:10 - before -> 3
• 整数在进行布尔运算时会根据其是否大于零转换为布尔值 例如:-3 -> false 例如:0 -> false 例如:3 -> true

• before:已经报名的学生的集合 例如:{20220101、20220202}
• new:想要报名的学生 例如:20220303
• after:新学生报名后的学生集合 定义:final = initial | delta 例如:{20220101、20220202、20220303}

true 或 false,表示新学生是否可以报名

请参考 example.signup。