根据SICP的评估环境模型进行词汇和动态范围界定 [英] Lexical vs dynamic scoping in terms of SICP's Environment Model of Evaluation

问题描述

在 根据每次应用功能时，都会创建一个新框架(用E1至E4标记)，该框架代表符号和值之间的一组绑定.当符号未绑定到框架中时，将查询该框架的封闭环境以绑定该特定符号.

Each time a function is applied, a new frame is created (labeled by E1 through E4) which represents a set of bindings between symbols and values. When a symbol is not bound in a frame, that frame's enclosing environment is queried for a binding of that particular symbol.

关于此图的有趣之处在于，所有由E标记的帧都包含在全局环境中.文字解释说这是因为这些功能是在全局环境中定义的，但并未对此问题进行详细说明:

The interesting thing about this diagram is that all the frames labelled by E is contained in the global environment. The text explains that this is because the functions was defined in the global environment, but does not elaborate on the issue:

请注意，由square创建的每个框架都指向全局环境，因为这是square过程对象指示的环境.

Notice that each frame created by square points to the global environment, since this is the environment indicated by the square procedure object.

如果取而代之的是在调用该函数的环境中包含框架，例如E3包含在E2中，而E2包含在E1中，那将是动态范围语言的有效模型作品?另外，由于Scheme在词法范围内，图中的框架具有相同的父"环境吗?

If instead frames where contained in the environment that the function was called in, say E3 was contained in E2 which in turn was contained in E1, would that be a valid model of how a dynamically scoped language works? Also, is the way that the frames in the diagram have the same 'parent' environment because Scheme is lexically scoped?

推荐答案

两个问题的答案都是是. SICP的这一章在不实际使用术语的情况下解释了词法范围.如您所描述的那样更改评估机制将创建一个动态范围的模型.

The answer to both questions is yes. That chapter of SICP is explaining lexical scope without actually using the term. Changing the evaluation mechanism as you describe would create a dynamically-scoped model.

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