Markdown之EBNF语法介绍(二十七)

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1.前言

本篇目的：Markdown之扩展Backus-Naur语法介绍。

2.扩展Backus-Naur语法介绍

• 扩展的 Backus-Naur 形式 （EBNF）是一种形式化的语法，用于指定编程语言或其他形式化语言的结构。它是Backus-Naur形式（BNF）的扩展，最初由John Backus和Peter Naur开发，用于描述Algol编程语言的语法。
• EBNF在原来的BNF元符号的基础上增加了几个额外的元符号，这使得语言的语法规范更加简洁和易读。它常用于编程语言的规范，有时也- 用于描述其他类型的形式语言的语法，如数据库查询语言或标记语言。
• 在PlantUML中已经引入了对EBNF的基本支持。

3.最小二进制图

@startebnf
binaryDigit = "0" | "1";
@endebnf

4.所有EBNF元件

• 介绍了PlantUML处理的EBNF元素

@startebnf
title All EBNF elements managed by PlantUML

(* Nodes *)
litteral = "a";
special = ? a ?;
rule = a;

(* Edges *)
required = a;
optional = [a];

zero_or_more = {a};
one_or_more = a, {a};
one_or_more_ebnf = {a}-;

zero_or_more_with_separator = [a, {',', a}];
one_or_more_with_separator = a, {',', a};
zero_or_more_with_terminator = {a, ','};
one_or_more_with_terminator = a, ',', {a, ','};
one_or_more_with_terminator_ebnf = {a, ','}-;

alternative = a | b;
group = (a | b) , c;
without_group = a | b , c;
@endebnf

5.特殊序列管理 special-sequence-symbol “?”

• 可以使用 special-sequence-symbol “?” 管理特殊序列

@startebnf
(* Example from §8.1 ISO-EBNF *)

h-tab = ? IS0 6429 character Horizontal Tabulation ? ;

new-line = { ? IS0 6429 character Carriage Return ? },
? IS0 6429 character Line Feed ?,
{ ? IS0 6429 character Carriage Return ? };

(* Other possible examples: *)
h-tab = ?Unicode U+0009?;
empty-special = ??;
@endebnf

6.完全重复管理 repetition-symbol “*”

• 可以使用 repetition-symbol “*” 管理重复。

@startebnf
(* Simplified Fortran example *)
Fortran_77_continuation_line = 5 * " ",  '[...]', 66 * [character];

(* Minimal test *)
test = 4 * '2';

(* Example of §5.7 Syntactic-factor of ISO EBNF *)
aa = "A";
bb = 3 * aa, "B";
cc = 3 * [aa], "C";
dd = {aa}, "D";
ee = aa, {aa}, "E";
ff = 3 * aa, 3 * [aa], "F";
gg = 3 * {aa}, "D";
@endebnf

7.绘图模式

• 可以选择绘图模式，并使用 !pragma compact 命令选择压缩模式。
• 扩展模式（默认）

@startebnf
title Expanded mode

zero_or_more = {a};
one_or_more = a, {a};
one_or_more_ebnf = {a}-;

zero_or_more_with_separator = [a, {',', a}];
one_or_more_with_separator = a, {',', a};
zero_or_more_with_terminator = {a, ','};
one_or_more_with_terminator = a, ',', {a, ','};

@endebnf

• 压缩模式

@startebnf
!pragma compact
title Compacted mode

zero_or_more = {a};
one_or_more = a, {a};
one_or_more_ebnf = {a}-;

zero_or_more_with_separator = [a, {',', a}];
one_or_more_with_separator = a, {',', a};
zero_or_more_with_terminator = {a, ','};
one_or_more_with_terminator = a, ',', {a, ','};

@endebnf

8.关于元素的说明

• 可以使用 EBNF 注释标签将注释添加到图表的元素中。

@startebnf
title Comments
(* Notes for Rule1 *)
Rule1 = {"a-z" (* any letter *) };
(* Notes for Rule2 *)
Rule2 =;
(* Additional notes and references *)
@endebnf

9.使用全局样式

• 不带样式（默认模式）

@startebnf
title Title
not_styled_ebnf = {"a", c , "a" (* Note on a *)}
| ? special ?
| "repetition", 4 * '2';
(* Global End Note *)
@endebnf

• 带有风格
• 可以使用样式来更改元素的渲染。

@startebnf
<style>
element {
  ebnf {
    LineColor blue
    Fontcolor green
    Backgroundcolor palegreen
    note {
      Backgroundcolor pink
    }
  }
}
</style>
title Title
styled_ebnf = {"a", c , "a" (* Note on a *)}
| ? special ?
| "repetition", 4 * '2';
(* Global End Note *)
@endebnf

10.LISP语法示例

• 使用 PlantUML 的 LISP 语法。

@startebnf
title LISP Grammar
grammars_expression = atomic_symbol | "(", s_expression, ".", s_expression, ")" | list;
list = "(", s_expression, { s_expression }, ")";
atomic_symbol = letter, atom_part;
atom_part = empty | letter, atom_part | number, atom_part;
letter = ? a-z ?;
number = ? 1-9 ?;
empty = " ";
@endebnf

11.Java语言规范

@startebnf
CompilationUnit = OrdinaryCompilationUnit | ModularCompilationUnit;
OrdinaryCompilationUnit = [PackageDeclaration], {ImportDeclaration}, {TopLevelClassOrInterfaceDeclaration};
ModularCompilationUnit = {ImportDeclaration}, ModuleDeclaration;
PackageDeclaration = {PackageModifier}, "package", Identifier, {Identifier}, ";";
PackageModifier = Annotation;
ImportDeclaration = SingleTypeImportDeclaration | TypeImportOnDemandDeclaration | SingleStaticImportDeclaration | StaticImportOnDemandDeclaration;
SingleTypeImportDeclaration = "import", TypeName, ";";
TypeImportOnDemandDeclaration = "import", PackageOrTypeName, ".*", ";";
SingleStaticImportDeclaration = "import", "static", TypeName, ".", Identifier, ";";
StaticImportOnDemandDeclaration = "import", "static", TypeName, ".*", ";";
TopLevelClassOrInterfaceDeclaration = (ClassDeclaration | InterfaceDeclaration), ";";
ModuleDeclaration = {Annotation}, [open], "module", Identifier, {Identifier}, "{", {ModuleDirective} "}";
ModuleDirective = ("requires", {RequiresModifier}, ModuleName, ";") | ("exports", PackageName, ["to", ModuleName {"," ModuleName}], ";") | ("opens", PackageName, ["to" ModuleName {"," ModuleName}], ";") | ("uses", TypeName, ";") | ("provides", TypeName, "with", TypeName {"," TypeName}, ";");
RequiresModifier = "transitive" | "static";
@endebnf

• Lexical Structure 词汇结构

@startebnf
Identifier = ?IdentifierChars but not a ReservedKeyword or BooleanLiteral or NullLiteral?;
IdentifierChars = JavaLetter, {JavaLetterOrDigit};
JavaLetter = ? any Unicode character that is a "Java letter" ?;
JavaLetterOrDigit = ? any Unicode character that is a "Java letter-or-digit" ?;
TypeIdentifier = ? Identifier but not permits, record, sealed, var, or yield ?;
UnqualifiedMethodIdentifier = ? Identifier but not yield ?;
Literal = IntegerLiteral | FloatingPointLiteral | BooleanLiteral | CharacterLiteral | StringLiteral | TextBlock | NullLiteral;
@endebnf