Racket中的一些宏术语
我很长一段时间都对这些术语感到困惑，认为最好问问它们到底是什么意思：
A.语法。 B. 语法值。 C. 语法对象。 Ds-表达式 E.datum（语法->datum）
- s-表达式和符号有什么区别？
- s-表达式和数据有什么区别？
- (语法、语法值和语法对象) 与 s-表达式 有什么区别？
- 用于解释的代码示例将不胜感激。
I am confused by the terms for a long time, thinking it is good to ask out what exactly do they mean:
A. syntax. B. syntax value. C. syntax object. D.s-expression E.datum (in syntax->datum)
- What's the difference between s-expression and symbol?
- What's the difference between s-expression and datum?
- What's the difference between (syntax, syntax values and syntax object) from s-expression?
- Code examples for explanation will be appreciated.
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“语法”是 Racket 中表示源代码的一种类型，它是 S 表达式的包装器（请参阅 最近的博客文章了解详细信息）。 “语法值”和“语法对象”都是这个的同义词，古代处理语法的
mzscheme语言函数在名称中使用了syntax-value。如今，我们更频繁地使用“语法”，而对于复数形式，我们使用“语法”。“S-表达式”要么是可以在代码中键入的原始数据片段（符号、数字、字符串、布尔值等——在 Racket 中，您还可以包含其他类型），要么是这些内容的列表。因此，S 表达式是由这些边缘原始类型组成的列表的任何嵌套结构。有时这也包括向量（因为它们可以使用
#(...)语法输入），但更常见的是它们被忽略。最后，“datum”是 S 表达式的另一个名称，有时当您想要引用它是具有输入表示形式的数据片段这一事实时。您可以查看 R5RS 如何介绍它：
至于你的问题：
s-表达式和符号有什么区别？
符号是S-表达式，S-表达式可以包含符号。
s-表达式和数据有什么区别？
其实没什么。 （尽管可能存在一些微妙的意图差异。）
（语法、语法值和语法对象）与 s-表达式之间有什么区别？
它们是racket中宏使用的程序语法的表示形式——它们包含 S-表达式，但它们添加源位置信息、词汇上下文、语法属性和证书。请参阅该博客文章以获取快速介绍。
"Syntax" is a type for representing source code in Racket, which is a wrapper around S-expression (see a recent blog post for details). "Syntax value" and "syntax object" are all synonyms of this, and ni the ancient days of the
mzschemelanguage functions that deal with syntax usedsyntax-valuein the name. These days we use just "syntax" more often, and for a plural form we use "syntaxes".An "S-expression" is either a primitive piece of data that can be typed in code (symbols, numbers, strings, booleans, etc -- in Racket you could also include other types), or a list of these things. An S-expression is therefore any nested structure of lists made of these primitive types at the fringe. Sometimes this includes vectors too (since they can be typed in using the
#(...)syntax) but more usually they're left out.Finally, "datum" is another name for an S-expression, sometimes when you want to refer to the fact that it's a piece of data that has an input representation. You can see how R5RS introduces it:
<Datum>may be any external representation of a Scheme object [...]. This notation is used to include literal constants in Scheme code.As for your questions:
What's the difference between s-expression and symbol?
A symbols is an S-expression, an S-expression may contain symbols.
What's the difference between s-expression and datum?
Nothing really. (Although some subtle intentions differences might be there.)
What's the difference between (syntax, syntax values and syntax object) from s-expression?
They are the representation of program syntax used by macros in racket -- they contain the S-expressions, but they add source location information, lexical context, syntax properties, and certificates. See that blog post for a quick introduction.