GXL 语法（对齐当前代码）

本文档按当前解析器实现整理（src/parser/*）。

1. 顶层结构

GXL 文件由多个 mod 组成：

mod main {
  env default {
    ROOT = "./";
  }

  flow conf {
    gx.echo(value: "hello");
  }
}

也支持 extern mod（外部模块引用）：

extern mod os,ssh { path = "./_gal/mods"; }
extern mod net { git = "https://example.com/repo.git", branch = "main"; }

2. 语法骨架

GxlFile      = { ExternMod | Module } ;

ExternMod    = "extern" "mod" ModNameList ModAddr ;
ModNameList  = Name { "," Name } ;
ModAddr      = "{" ( "path" "=" String
                 | "git" "=" String [ "," ("branch"|"channel") "=" String ] [ "," "tag" "=" String ] ) "}" ;

Module       = [Annotation] "mod" Name [":" MixList] "{" { Prop | Env | Flow | Fun | Activity } "}" [";"] ;
Env          = [Annotation] "env" Name [":" MixList] (";" | "{" { Prop | EnvStmt } "}" [";"]) ;
Flow         = [Annotation] "flow" FlowHead (";" | Block [";"]) ;
Fun          = "fn" Name "(" [FunParams] ")" (";" | Block [";"]) ;
Activity     = "activity" Name "{" { FormalParam [","|";" ] } "}" ;

FlowHead     = Name [":" FlowList [":" FlowList]]
             | [FlowPipe "|"] "@" Name ["|" FlowPipe]
             | Name ["|" FlowPipe] ;
FlowPipe     = FlowRef { "|" FlowRef } ;
FlowList     = FlowRef { "," FlowRef } ;
FlowRef      = Name | Name "." Name | VarRef ;
MixList      = MixItem { "," MixItem } ;
MixItem      = Name | VarRef ;

Block        = "{" { Prop | IfStmt | ForStmt | Builtin | Call | CmdBlock } "}" ;
IfStmt       = "if" Expr Block { "else" "if" Expr Block } [ "else" Block ] ;
ForStmt      = "for" VarRef "in" VarRef Block ;
CmdBlock     = "```cmd" <raw text> "```" ;

Prop         = Name "=" GxlObject (","|";") ;
GxlObject    = VarRef | Scalar | List | Object ;
Object       = "{" [ ObjItem {"," ObjItem} ] "}" ;
ObjItem      = Name ":" ScalarOrNested ;
List         = "[" [ ScalarOrNested {"," ScalarOrNested} ] "]" ;

Builtin      = gx.xxx call syntax ;
Call         = Path "(" [ActualParams] ")" [";"] ;
Annotation   = "#[" AnnFun {"," AnnFun} "]" ;

3. Flow 头部支持形式

3.1 旧式（冒号）

flow test : pre1,pre2 : post1,post2 {
  gx.echo(value: "run");
}

3.2 管道 + @ 指定主 flow

flow pre1 | pre2 | @test | post1 | post2 {
  gx.echo(value: "run");
}

3.3 简写管道

flow test | post1 | post2 {
  gx.echo(value: "run");
}

4. 参数与调用约定

所有内置能力统一使用调用形式：

gx.cmd(cmd: "echo hello");
gx.echo("hello");              // 等价，匿名参数映射到 default

说明：

• 调用参数分隔符是 ,。
• 命名参数使用 :，如 name: "v"。
• 很多能力支持 default（匿名首参数）写法。

5. 条件表达式

支持：

• 比较：== != > >= < <= =*（=* 为通配）
• 逻辑：&& || !
• 函数：defined(${VAR})

示例：

if defined(${CUR.ENABLE}) && ${CUR.ENABLE} == true {
  gx.echo(value: "enabled");
} else {
  gx.echo(value: "disabled");
}

6. 目前块内可直接识别的内置能力

• gx.cmd
• gx.shell
• gx.run
• gx.echo
• gx.assert
• gx.ver
• gx.read_file
• gx.read_cmd
• gx.read_stdin
• gx.tpl
• gx.tar
• gx.untar
• gx.download
• gx.upload
• gx.patch_file

补充：

• gx.vars 只在 env 块中使用。
• defined(...) 是表达式函数，不是 gx.defined 命令。