peggy

• peggyjs/peggy
  • PEG.js 后继
• 参考
  • https://github.com/peggyjs/peggy/blob/main/src/parser.pegjs
  • https://peggyjs.org/online
  • metadevpro/ts-pegjs
    • TS code generation plugin for peggy
  • Formatter https://siefkenj.github.io/prettier-pegjs-playground/
  • examples
    • https://github.com/alsotang/sql.pegjs/blob/master/lib/sql.pegjs
    • https://www.sqlite.org/syntaxdiagrams.html
• PEG.js 之后新功能
  • Global Initializers {{}}
    • 全局
    • {} 初始化是每次 parse 都会创建 - 能访问 options
  • value plucking @
  • typescript
  • source maps
• options
  • grammarSource
  • startRule

npx -y peggy ./parser.pegjs --format es

flag	for
--allowed-start-rules <rules>	默认第一个,逗号分隔指定多个,* for all
--ast	输出内部 AST 代替 parser 源码
--cache	缓存结果,避免指数级解析时间,但解析会更慢
-d, --dependency <[name:]module>	依赖
-D, --dependencies <json>	依赖
--dts	生成 .d.ts 文件
-e, --export-var <variable>	全局变量
--extra-options <options>	额外选项 for peg.generate, json object
-c, --extra-options-file <file>	额外选项
--format <format>	输出格式, amd, commonjs, globals, umd, es
-o, --output <file>	输出文件
--plugin	插件
-m, --source-map <file>	生成 source map
--return-types <JSON object>	返回类型, for --dts
-S, --start-rule <rule>	指定 start rule
-t, --test <text>	测试
-T, --test-file <text>	测试
--trace	追踪
-w,--watch	监听

config.cjs

module.exports = {
  allowedStartRules = ["foo", "bar"],
  format: "umd",
  exportVar: "foo",
  input: "fooGrammar.peggy",
  plugins: [require("./plugin.js")],
  testFile: "myTestInput.foo",
  trace: true,
};

plugin.ts

export function use(config:{parser:Parser,reservedWords,passes:{ [stage: string]: Pass[] } }, options) => {
}

import peggy from 'peggy';
const parser = peggy.generate("start = ('a' / 'b')+");

const parser = peggy.generate([
  { source: 'file1.peggy', text: "numbers = number|.., ','|" },
  { source: 'lib.peggy', text: 'number = n:$[0-9]+ { return parseInt(n, 10) }' },
]);

syntax	for
"a",'a'	匹配 a
'a'i	匹配 a 或 A
.	匹配任意
!.	EOF, EOI, End of Input
[ab]	匹配 a 或 b
<rule>	匹配 rule
(expr)	分组
expr *,expr +,expr ?	重复
& expr	positive assertion, lookahead
! expr	negative assertion, lookahead
& { predicate }	code block
! { predicate }	code block
$ expr	-> {return text();} - 语法糖
label: expr	定义 label/变量
@(label:)? expr	返回 label 作为内容 - pluck
expr1 expr2	顺序匹配
expr { action }	执行脚本
expr1 / expr2	alternate , choose
expr |COUNT|
expr |COUNT,SEQ|
expr |MIN..MAX|
expr |MIN..MAX,SEP|
expr |..|	-> expr*
expr |0..|	-> expr*
expr |1..|	-> expr+
expr |..1|	-> expr?

// use runtime value as option
start = count:n1 "a"|count|;
n1 = n:$[0-9] { return parseInt(n); };

start = "a"|{ return options.count; }|;

• min,max,count 可以是 label/变量/code block

start = "a"|{ return options.count; }|;

// 手写
Values = next:(a:Value _ b:(_ ',' _ next:Value {return next})* ','? {return b?[a,...b]:a})? {return next || []}
// repeat
Values = next:(Value|..,","|)  ','?  {return next || []}

• https://github.com/peggyjs/peggy/blob/main/lib/peg.d.ts

Action Execution Environment

• () 会形成变量作用域
• input - parse 参数
• options - parse 参数
• error(message,where=location()) - 返回错误
• expected(message, where=location())
• location() - {source:options.grammarSource,start:{offset,line,column},end}
• range() 只返回 offset 对象
• offset() -> location().start.offset
• text()
• reserved/保留关键词
  • count

{{
  // 全局初始化 - 定义的方法和变量全局有效
}}

{
  // parser 初始化
}

list = head:word tail:(_ "," _ @word)* { return [head, ...tail]; }
word = $[a-z]i+
_ = [ \t]*
__ "whitespace" // human-readable name
  = [ \t]+

// 引入另外的 rule
import {number} from "./number.js"
a = number|1.., "," WS|
WS = [ \t]*

list
  = word|.., delimiter| delimiter?
delimiter
  = _ "," _
word
  = $[a-z]i+
_
  = [ \t]*