DDMathParser:解析包含if语句的公式 [英] DDMathParser: Parsing formulas which contain if statements

问题描述

我已经开始在当前项目中实现DDMathParser，并使用此框架结合字典中给出的变量(变量替换)来计算公式的结果.

I have started to implement DDMathParser in my current project and I use this framework to calculate the results of formulas in combination with variables given in a dictionary (variable substitution).

是否可以在公式中使用类似if语句的内容，例如"if ($a > 0) { $b / $c } else {$b * 1000}?

Would it be possible to use something like if statements in the formulas, e.g. "if ($a > 0) { $b / $c } else {$b * 1000}?

我认为if语句的创建方式可以与新函数类似(如 DDMathParser Wiki ).如果是这样的话，如果有人可以向我展示如何做到这一点，我将感到非常高兴.

I assume that if statements could be created in a similar way than new functions (as described in the DDMathParser Wiki). If this would be the case, I would be glad if someone could show me how to do this.

关于如何在DDMathParser中使用if语句的任何想法或提示?

Any ideas or hints on how to use if statements in DDMathParser?

谢谢！

推荐答案

DDMathParser作者在这里...

这实际上是不可能的，但这不是您想的原因. DDMathParser可以很好地解析if.这是花括号，它将有问题.您也许可以这样做:

This isn't really possible, but not for the reason you think. DDMathParser can parse if just fine. It's the curly braces it would have issues with. You could maybe do:

if ($a > 0) ($b / $c) else ($b * 1000)

这将被解析为:

if($a > 0) * ($b / $c) * else($b *1000)

NSLogged的哪个是:

multiply(multiply(if(l_gt($a,0)),divide($b,$c)),else(multiply($b,1000)))

因此，您可以执行此操作，但是尝试自己进行范围确定将是一件很痛苦的事情.我认为将字符串预分解成各个部分可能会更容易:

So, you could do it, but it would be a total pain to try and handle the scoping yourself. I think it'd probably be easier to pre-parse the string into various parts:

if ($a > 0) => if(l_get($a, 0))
($b / $c) => divide($b, $c)
($b * 1000) => multiply($b, 1000)

然后自己处理.

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