在 Scratch 中模拟自定义报告块？

Question

在 Scratch 2.0 中，添加了对自定义堆栈块 (procedures) 的支持。但是有什么方法可以将此用于 "abstract away" 逻辑，即 returns 一个值？

例如，我这里有一个简单计算指数的脚本：(view graphic representation)

set [base v] to [2]
set [index v] to [3]
... // above is for initializing
set [result v] to (base)
repeat until <(index) = [1]>
  set [result v] to ((result) * (base))
  change [index v] by (-1)

如何将此逻辑导出到 "custom reporter" 以供重用？

Answer 1

最简单的方法是创建自定义命令方块，并将 return 值存储在变量中。这有一些缺点，例如不允许递归调用，但在大多数情况下都有效。我还建议在不刷新屏幕的情况下将块设置为运行。

像这样简单地定义它，return 值可用 result:

define (base) ^ (exp)
set [index v] to (exp) // need a variable, as arguments are immutable
set [result v] to (base)
repeat until <(index) = [1]>
  set [result v] to ((result) * (base))
  change [index v] by (-1)

然后可以这样调用：

when gf clicked
(4) ^ (3) // the stack block
say (join [4 ^ 3 = ] (result)) // result is set by the [()^()] block

See this in rendered ScratchBlocks.

Answer 2

还有第二种更复杂的方法。它允许递归块，并且您可以多次运行一个块。我称它为堆叠方法，因为我使用列表作为堆栈。有关示例，请参阅 this project that i made.

这种方法也不会弄乱变量面板。

define (base) ^ (index) recursive
if <(index) = [1]>
  add (base) to [stack v]
else
  (base) ^ ((index) - (1)) recursive // adds the previous item to the stack
  add ((base) * (item (last v) of [stack v])) to [stack v]
  delete ((length of [stack v]) - (1)) of [stack v] // clean up

然后可以使用与我在中解释的基本相同的方法访问它：

when gf clicked
(4) ^ (3) recursive // the stack block
say (join [4 ^ 3 = ] (item (last v) of [stack v])) // get the item from the end of the stack
delete [last v] of [stack v] // optional, if you want to clean up

See this in rendered ScratchBlocks.

Answer 3

这是一个例子 (rendered):

define split [text] by [splitter]
delete (all v) of [output list v]
set [parse v] to [0]
set [cur string v] to []
repeat until ((parse) > (length of (splitter))
   if <(letter (parse) of (text)) = (splitter)> then
      add (cur string) to [output list v]
      set [cur string v] to []
   else
      set [cur string v] to (join (cur string) (letter (parse) of (text)))
   end
end

when GF clicked
split [Hello, world! Do you like this?] by [ ] // That's a space.

// That should output a list: ["Hello,", "world!", "Do", "you", "like", "this?"]

define the answer to life
set [output var v] to (42)

when GF clicked
the answer to life
say (output var)

它展示了如何使用列表输出和变量输出。

在 Scratch 中模拟自定义报告块？

Simulating a custom reporter block in Scratch?

mit-scratch