Question

假设我想生成此输出：

  public  String toString() {
         return this.getFirstName() + "," + this.getLastName() + "," + this.getAge();
  }

来自下面的模板和自定义递归构建标记函数：

  template-toString: {this.get<%property%>() <%either not context.build-markup/EOB [{+ "," +}][""]%> }

  build-markup/vars template-toString [property] ["FirstName" "LastName" "Age"]

我的问题是避免最后一个元素与{+“，”+}

连接

我的想法是使用带有EOB属性（End Of Block）的context.build-markup，当处理最后一个元素时，该属性将设置为true。然后我可以使用上面的template-toString，而不是context.build-markup / EOB [{+“，”+}] [“”]连接或不连接{+“，”+}：

context.build-markup: context [

  EOB: false

  set 'build-markup func [
      {Return markup text replacing <%tags%> with their evaluated results.} 
      content [string! file! url!] 
      /vars block-fields block-values
      /quiet "Do not show errors in the output." 
      /local out eval value n max i
  ][

    out: make string! 126 

    either not vars [
        content: either string? content [copy content] [read content] 

        eval: func [val /local tmp] [
            either error? set/any 'tmp try [do val] [
                if not quiet [
                    tmp: disarm :tmp 
                    append out reform ["***ERROR" tmp/id "in:" val]
                ]
            ] [
                if not unset? get/any 'tmp [append out :tmp]
            ]
        ] 
        parse/all content [
            any [
                end break 
                | "<%" [copy value to "%>" 2 skip | copy value to end] (eval value) 
                | copy value [to "<%" | to end] (append out value)
            ]
        ]
      ][          


          n: length? block-fields

          self/EOB: false

          actions: copy []

          repeat i n [



            append actions compose/only [

              ;set in self 'EOB (i = n)
              set in system/words (to-lit-word pick (block-fields) (i)) get pick (block-fields) (i)
            ]

          ]
          append actions compose/only [            
              append out build-markup content            
          ]
          foreach :block-fields block-values actions



          if any [(back tail out) = "^/" (back tail out) = " " (back tail out) = "," (back tail out) = ";" (back tail out) = "/" (back tail out) = "\"] [
            remove back tail out
          ]        
      ] 
      out
  ]

]

但我的尝试失败了（所以我评论说;设置为自我'EOB（i = n），因为它不起作用）。如何纠正代码以获得我想要的东西？

Answer 1

我很确定你能以比这更清洁的方式实现你的目标。无论如何，我可以告诉你为什么你在做什么不起作用！

n表达式length? block-fields，repeat循环上升到n。但block-fields包含单个参数[property]！因此，它从1循环到1。

你想要想要针对枚举block-values（在此示例中范围从1到3）的内容进行测试，然后在索引达到3时唯一地处理它。换句话说，您的set in self 'EOB表达式必须是block-values而不是block-fields的枚举的一部分。

这会给你你想要的行为：

n: length? block-values
i: 1
foreach :block-fields block-values compose/only [
    set in self 'EOB equal? i n
    do (actions)
    ++ i
]

这绝对不行：

append actions compose/only [
    set in self 'EOB (i = n)
    set in system/words (to-lit-word pick (block-fields) (i)) get pick (block-fields) (i)
]

...因为您正在处理i和n均为1的情况，对于此循环的单次迭代。这意味着(i = n)是真的。因此，您为“行动”获得的元代码就是：

[
    set in self 'EOB true 
    set in system/words 'property get pick [property] 1
]

接下来，您使用多余的组合运行代码（因为没有PAREN！s，您可以省略COMPOSE / ONLY）：

append actions compose/only [
    append out build-markup content
]

这显然会为您的actions元代码添加一行：

[
    set in self 'EOB true 
    set in system/words 'property get pick [property] 1 
    append out build-markup content
]

按照惯例，我建议您学会使用PROBE和PRINT来查看并检查每个阶段的期望。 Rebol很适合转储变量等......

Answer 2

你似乎把简单的东西弄得很复杂：

>> a: make object! [                           
[    b: false                
[    set 'c func[i n] [b: i = n]
[    ]
>> a/b
== false
>> c 1 4
== false
>> a/b 
== false
>> c 1 1
== true
>> a/b
== true

上下文和属性的问题

2 个答案: