(*
some choose:
1. does not support ++ and -- operator, and use -- to begin comment, like lua.
2. integral division use 'div', modular division use 'mod'
 BTW, 'div' and 'mod' can also use as nomal, for example 'math.div'

 *)

module ::= stats

stats ::= {stat [';']}

block ::= '{' stats '}'

stat ::= block
 | 'if' exp block {'elseif' exp block} ['else' block]
 | 'while' exp block 
 | 'do' block 'while' exp 
 | 'for' Name '=' exp ',' exp [',' exp] block 
 | 'for' Name [',' Name] 'in' exp block 
 | 'for' block 
 | 'break' 
 | 'continue' 
 | 'try' block ['catch' [Name] block] ['finally' block] 
 | 'throw' [explist] 
 | scope_head+ block 
 | 'fn' funcname funcbody 
 | 'return' [explist] 
 | ('global'|'local') namelist ['=' explist] 
 | ('global'|'local') 'fn' Name funcbody 
 | varlist '=' explist 
 | var self_assign exp
 | funccall

scope_head ::= 'scope' '(' (namelist '=' explist | explist) ')'

# 语法糖,支持一部分吧
self_assign ::= '+=' | '-=' | '*=' | '/=' | '&=' | '|=' | '^=' | '.='

namelist ::= Name {',' Name}

varlist ::= var {',' var}

var ::= Name [{index | args } index]

funccall ::= Name {index | args} args [String]

funcname ::= Name {'.' Name}

funcbody ::= ['(' [paramlist [',']] ')'] block

paramlist ::= Name (',' Name )* [',' '*' Name] | '*' Name

explist ::= {exp ','} exp

array_def ::= '[' [exp {',' exp} [',']] ']'

table_def ::= '{' [field {',' field} [',']] '}'

field ::= '[' exp ']' '=' exp | Name '=' exp

exp_or_stat ::= exp | 'throw' [explist] | 'break' | 'continue' | 'return' [explist]

exp ::= q_exp | exp binop exp | unop exp | main_exp

primary_exp ::= 'nil' | 'false' | 'true' | Number | String
 | fn funcbody | table_def | array_def
 | '(' exp ')'
 | Name

main_exp ::= primary_exp {index | args} [String]

q_exp ::= exp '?' exp ':' exp_or_stat
 | exp '?:' exp_or_stat | exp '??' exp_or_stat

function ::= 'fn' funcbody

index ::= '[' exp ']' | '.' Name

args ::= '(' [(args_three | args_two | args_one) [','] ] ')'

args_one ::= exp {',' exp}
args_two ::= [args_one ','] '*' exp
args_three ::= [args_two ','] Name ':' exp {',' Name ':' exp }

binop ::= 'or' | 'and'
 | '<' | '<=' | '>' | '>=' | '==' | '!='
 | '..'
 | '|' | '~' | '&' | '<<' | '>>' | '>>>'
 | '+' | '-' 
 | '*' | '/' | 'div' | 'mod'
 | '^'

unop ::= '-' | 'not' | '~'