有短路乘法吗? [英] Is there such a thing as short circuit multiplication?

问题描述

我们都知道逻辑表达式中的短路，即何时

We all know about short circuiting in logical expressions, i.e. when

if ( False AND myFunc(a) ) then
...

不必费心执行myFunc()，因为if条件不可能成立.

doesn't bother executing myFunc() because there's no way the if condition can be true.

我很好奇您的日常代数方程式是否相等

I was curious as to whether there is an equivalent for your everyday algebraic equation, say

result = C*x/y + z

如果C=0，则没有必要评估第一个项.如果x和y是标量，则在性能上并没有多大关系，但是如果我们假装它们是大型矩阵，并且运算成本很高(并且适用于矩阵)，那么肯定会有所作为.当然，您可以通过抛出if C!=0语句来避免这种极端情况.

If C=0 there is no point in evaluating the first term. It wouldn't matter much performance-wise if x and y were scalars, but if we pretend they are large matrices and the operations are costly (and applicable to matrices) then surely it would make a difference. Of course you could avoid such an extreme case by throwing in an if C!=0 statement.

所以我的问题是这样的功能是否存在以及是否有用.我不是一个程序员，所以可能是以我没遇到过的名字来做的.如果是这样，请赐教:)

So my question is whether such a feature exists and if it is useful. I'm not much of a programmer so it probably does under some name that I haven't come across; if so please enlighten me :)

推荐答案

您所讨论的概念有不同的名称:惰性评估，非严格评估， 按需呼叫，仅举几例，实际上比避免在这里和那里乘法的功能要强大得多.

The concept you are talking about goes under different names: lazy evaluation, non-strict evaluation, call by need, to name a few and is actually much more powerful than just avoiding a multiplication here and there.

有些编程语言例如 Haskell 或弗雷格(Frege)的评估模型是非严格的.编写短路"乘法运算符非常容易，例如，您可以编写以下内容:

There are programming languages like Haskell or Frege whose evaluation model is non-strict. There it would be quite easy to write your "short circuiting" multiplication operator, for example you could write something like:

infixl 7 `*?`        -- tell compiler that ?* is a left associative infix operator
                     -- with precedence 7 (like the normal *)

0 *? x = 0           -- do not evaluate x
y *? x = y * x       -- fall back to standard multiplication

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