在Mathematica中打印符号名称和值 [英] Printing symbol name and value in Mathematica

问题描述

我想创建一个函数My`Print[args__]，该函数打印我传递的符号的名称以及它们的值.问题在于，在将符号传递给My`Print之前，需要对它们进行评估.因此My`Print永远都看不到符号名称.

I'd like to create a function My`Print[args__] that prints the names of the symbols that I pass it, along with their values. The problem is that before the symbols are passed to My`Print, they're evaluated. So My`Print never gets to see the symbol names.

一种解决方案是用Unevaluated[]包围我传递给My`Print的每个参数，但这似乎很混乱.有没有一种定义MACRO的方式，当我键入My`Print[args__]时，Mathematica内核会看到My`Print[Unevaluated /@ args__]?

One solution is to surround every argument that I pass to My`Print with Unevaluated[], but this seems messy. Is there a way of defining a MACRO such that when I type My`Print[args__], the Mathematica Kernel sees My`Print[Unevaluated /@ args__]?

推荐答案

您需要设置属性这是可能的实现方式:

Clear[my`print]
SetAttributes[my`print, HoldAll]
my`print[args__] := 
 Scan[
  Function[x, Print[Unevaluated[x], " = ", x], {HoldAll}], 
  Hold[args]
 ]

我使用小写名称来避免与包中的内置函数或函数发生冲突.

I used lowercase names to avoid conflicts with built-ins or functions from packages.

仅需明确说明:我在这里有两个功能.一个将打印一个单个符号的值，并在其中实现为Function.如果足够，您可以单独使用它.另一个是实际的my`print函数.请注意，两者都必须具有HoldAll属性.

Just to make it explicit: I have two functions here. One will print the value of a single symbol, and is implemented as a Function inside. You can just use this on its own if it's sufficient. The other is the actual my`print function. Note that both need to have the HoldAll attribute.

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