Rexx 编程/如何使用 Rexx/goto

许多语言都有一个“jump”指令或“goto”语句，用于跳至程序的任意部分。其他语言通过更特定的流程控制结构完全取代了对这种语句的需求。Rexx 主要使用子例程和 DO/END 块来跳转到程序的不同部分，但它确实有一种更通用的跳转指令。你可以使用 SIGNAL 关键字将计算机重定向到程序中带标签的位置。标签以冒号结尾。

/* Jump around to validate input and factor a whole number. */
START:
 say "I can factor a positive whole number for you."
 say "First, enter a number of your choice:"
 signal GET_NUMBER
START_FACTORING:
 say "Here are the factors of" number":"
 possible_factor = 1
CHECK_FACTOR:
 if number // possible_factor = 0 then signal SHOW_FACTOR
 else signal NEXT_FACTOR
SHOW_FACTOR:
 say possible_factor
NEXT_FACTOR:
 possible_factor = possible_factor + 1
 if possible_factor > number then signal FINISHED
 signal CHECK_FACTOR
FINISHED:
 say "That's all!"
 exit
GET_NUMBER:
 pull number
CHECK_NUMBER:
 if DataType(number, "W") then signal POSITIVE?
 say "That's not even a whole number."
 signal GET_NUMBER
POSITIVE?:
 if number > 1 then signal START_FACTORING
 say "Positive, please!"
 signal GET_NUMBER

依赖 goto 语句的长程序众所周知从长期来看很难理解。坚持使用本书其他地方所述的结构化流程控制语句，比如 for 循环。编写此脚本的一种更简洁的方式（无需 SIGNAL 语句）如下

/* Greet the user and ask for a positive whole number. */
say "I can factor a positive whole number for you!"
say "First, enter a number of your choice:"
/* Make sure the user actually enters a positive whole number. */
do until whole? & positive?
 pull number
 whole? = DataType(number, "W")
 positive? = number > 0
 if \ whole? then say "That's not even a number!"
 else if \ positive? then say "Positive, please!"
end
/* Now show the factors */
say "Here are the factors of" number":"
do possible_factor = 1 to number
 if number // possible_factor = 0 then
  say possible_factor
end
say "That's all!"
exit