简化文法

program      → declaration* EOF ;
declaration  → "公"? ("令" | "定") IDENT type? "为" expression "；"
             | functionDecl
             | classDecl
             | importDecl
             | statement ;
type         → "：" typePrimary (("|") typePrimary)* ;
typePrimary  → TYPE_NAME "?"?
             | IDENT "<" type ("，" type)* ">"
             | "法" "（" (type ("，" type)*)? "）" "：" type ;
functionDecl → "异"? "法" IDENT "（" parameters? "）" type? "则" declaration* "终" ;
classDecl    → "公"? "类" IDENT ("承" IDENT)? ("纳" IDENT ("，" IDENT)*)?
               "则" classMember* "终" ;
classMember  → ("公" | "私" | "只" | "静")*
               (fieldDecl | functionDecl) ;
fieldDecl    → "域" IDENT type ("为" expression)? "；" ;
protocolDecl → "公"? "协" IDENT "则" (fieldDecl | functionSignature)* "终" ;
importDecl   → "引" STRING ("为" | "作") IDENT "；" ;
statement    → "置" (IDENT | member | index) "为" expression "；"
             | "言" expression "；"
             | "若" expression "则" declaration* ("否则" declaration*)? "终"
             | "当" expression "则" declaration* "终"
             | "逐" IDENT type? "于" expression "则" declaration* "终"
             | "试" "则" declaration* "救" IDENT "则" declaration* "终"
             | "抛" expression "；"
             | "归" expression? "；"
             | expression "；" ;
call         → primary (("（" arguments? "）") | ("." IDENT) | index | slice)* ;
index        → "【" expression "】" ;
slice        → "【" expression? "：" expression? "】" ;
primary      → literal | IDENT | list | tuple | map | "候" expression | "（" expression "）" ;
list         → "【" arguments? "】" ;
tuple        → "（" expression "，" (expression ("，" expression)*)? "）" ;
map          → "{" (expression "：" expression) ("，" ...)* "}" ;
expression   → 逻辑或、逻辑且、相等、比较、加减、乘除、一元、调用、原子表达式 ;