没有 ELSE 关键字的编程语言 - 是否更复杂？

发布于 2024-10-04 04:09:41 字数 960 浏览 9 评论 0原文

我正在为儿童开发一种简单的编程语言，基于 Karel。为了控制程序流程，我目前提供以下设施（以伪代码）：

定义无参数过程
if [not] EXPRESSION STATMENT
while [not] EXPRESSION STATMENT

我没有任何方法从过程中返回，并且 我不' t提供else语句。

以下面的代码为例：

if something
 statement1
if not something
 statement2

代码的执行流向if，执行statement1 if 某件事是真的；然后测试某事是否不成立（但程序的状态已更改！），然后执行statement2。 这可能会导致两个测试都成功。

这会限制程序员吗？到目前为止，我已经能够通过使用 if< 来解决所有示例问题/code> ... if not ...，或者先使用if not，然后使用if。

所以，我的问题是： 是否有必要添加 else 语句？ 关键字越多，语言就会变得越复杂。是否所有可以用 else 语句解决的问题在没有它的情况下也可以解决，尽管更复杂？

或者省略 else 语句实际上会使语言变得更加复杂且违反直觉？

原文

I'm working on a simple programming language for kids, based on Karel. For controlling program flow, I currently provide these facilities (in pseudocode):

defining parameterless procedures
if [not] EXPRESSION STATEMENT
while [not] EXPRESSION STATEMENT

I don't have any means to return from a procedure, and I don't provide the else statement.

Take the following code for an example:

if something
 statement1
if not something
 statement2

The execution of code flows to if, executing statement1 if something is true;
then testing if something is not true (but the state of the program has changed!), then executing statement2. This can lead to both tests succeeding.

Does this limit the programmer? So far I've been able to solve all of my example problems by just using if ... if not ..., or using if not first, then if.

So, my question is:
Is adding the else statement necessary? It would make the language a bit more complicated with having more keywords. Are all problems that would be solvable with else statement solvable also without it, albeit more complicated?

Or is omitting the else statement actually making the language more complicated and counter-intuitive?

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奢华的一滴泪 2024-10-11 04:09:41

如果某物的评估成本很高，那么您使用else的语言可能会出现问题，因为评估将执行两次。

另一个潜在的问题是，如果statement1可以修改something的值，您可能最终会两个测试都成功 - 如果您使用其他方法，则不会发生这种情况。

当然，可以通过将结果存储在临时局部变量中来缓解这些问题：

bool result = something
if result
    statement1
if not result
    statement2

所以不，您并没有限制程序员的可能性 - 使用 else 可以完成的所有事情都可以在没有它的情况下完成通过使用上述方法。但每次都要编写更多的代码，并且会给粗心的程序员带来一些新的潜在问题，如果您允许 else，这些问题就可以避免。

If something is expensive to evaluate then your language with else might give a problem because the evaluation will be performed twice.

Another potential problem is that if statement1 can modify the value of something you may end up with both tests succeeding - something that could not happen if you used else.

Of course these problems can be mitigated by storing the result in a temporary local variable:

bool result = something
if result
    statement1
if not result
    statement2

So no you aren't limiting the programmer in what is possible - everything that can be done with else can be done without it by using the above approach. But it is a little more code to write each time and it introduces a few new potential problems for the unwary programmer that would be avoided if you allowed else.

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