如何在不评估它们的情况下阻止符号? [英] How to Block Symbols without evaluating them?

问题描述

假设我有一个 Symbol 的名称列表:

Suppose I have a list of names of Symbols:

f1 := Print["f1 is evaluated!"];
list = {"f1", "f2"};

Block这些Symbol的显而易见的方法是对它们进行评估:

The obvious way to Block these Symbols leads to evaluation of them:

In[19]:= With[{list=Symbol/@list},Block[list,f1//ToString]]
During evaluation of In[19]:= f1 is evaluated!
During evaluation of In[19]:= f1 is evaluated!
Out[19]= Null

但无需评估，我们就可以阻止它们而不会出现任何问题:

But without evaluation we could Block them without any problem:

In[20]:= Block[{f1, f2}, f1 // ToString]
Out[20]= "f1"

是否可以在不评估 Symbol 的情况下将此列表注入 Block 范围?

Is it possible to inject this list into the Block scope without evaluating the Symbols?

推荐答案

这是实现此目的的另一种技术:

Here is yet another technique to do this:

SetAttributes[blockAlt,HoldRest];
blockAlt[s : {__String}, body_] :=
   Replace[Join @@ ToHeldExpression[s], Hold[x__] :> Block[{x}, body]]

由于规则的破坏性(它们不尊重其他作用域构造，包括它们自己)，我们在此保留纯函数

We save here on pure functions, due to the disruptive nature of rules (they don't respect other scoping constructs, including themselves)

编辑

另一种选择(甚至更短):

Yet another alternative (even shorter):

SetAttributes[blockAlt1, HoldRest];
blockAlt1[s : {__String}, body_] :=
   Block @@ Append[ToHeldExpression@ToString[s], Unevaluated[body]] 

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