syntax-rules是定义模式匹配宏的方法,它接受一组模式和一组模板,并返回一个宏转换规则函数。在模式匹配宏中,宏的输入会被与模式进行匹配,如果匹配成功,则使用模板生成新的语法对象。syntax-rules宏通常用来定义简单的宏,例如let宏和case宏。 总之,了解Scheme宏的来源需要熟悉define-syntax和syntax-rules这两个基...
syntax-rules的能力是受限的,不能引入新的syntax-object,只能写一些简单的宏.但是用syntax-rules写出来的宏肯定比用syntax-case或define-macro写的更优雅. syntax-case完全不受限制,扩展能力与传统lisp宏(defmacro)是一样的,但由于它自带模式匹配功能,所以写起来会更方便,至少quasiquote,unquote,unquote-splicing少了很...
In this case, the indirect object comes right after the verb, and the direct object comes after the indirect object. Keep in mind that objects of prepositions do not follow this pattern; for example, you can say, The dog gave the ball to me. 6 Subject → verb → direct object → ...
Python is case-sensitive (name and Name are different). Keywords like class, def, and return cannot be used as a variable name Example: Python 1 2 3 4 5 6 7 8 9 10 11 12 # Correct variable naming _valid_name = "Python" #Incorrect variable naming invalid-name = "Error" print(_...
Command syntax is case insensitive, and three- or four-letter abbreviations can be used for many command specifications. You can use as many lines as you want to specify a single command. You can add space or break lines at almost any point where a single blank is allowed, such as around...
(一、EQEQ25)有效期,(一、二5EQ)不是. 空白(不1995/32)单独使用,必须由相关机构所表现相比.4. 一变就比不上了一连串数字变化,反之亦然. 由于无法与一个比较合理的功能sysmis、失踪、任何范围或多项.5. 串用价值体现,必须要引用任何具体领导和厦门车. 小写字母被认为是有别于uppercase信.6. ...
They can be entered in uppercase or lowercase letters. If you use keywords as names of columns, tables, or database users, you must place them in double quotation marks. <xyz> Terms in angle brackets are placeholders for end symbols explained in this document. Do not use angle brackets ...
The text-editor will add a small hidden header (called UTF-BOM) at the beginning of the xml file in this case. Whitespace characters like blanks, tabs and line-breaks between xml-elements and between the xml-attributes will be ignored. But inside attribute-values they will be respected. ...
String values used in expressions must be specified in quotation marks and must include any leading or trailing blanks. Lowercase letters are distinguished from uppercase letters. To create a new string variable within a DO IF—END IF structure, you must first declare the variable on the STRING...
对于syntax-rules(),The Scheme Programming Language上面是这样描述的:While it ismuchless expressive than syntax-case, it is sufficient for defining many common syntactic extension。也就是说,它的表达能力是远弱于 syntax-case 的。syntax-case 在 r6rs 是标准实现所要求的,但是在 r7rs small 中被废除了,...