陳鍾誠

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Lua 的 BNF 語法

看完上述的 Lua 程式範例之後,讓我們來看看 Lua 程式語言的語法吧!

Lua 的語法非常精簡,可以列印在單一頁面中,以下是 Lua 的 BNF 語法。

	chunk ::= block

	block ::= {stat} [retstat]

	stat ::=  ‘;’ | 
		 varlist ‘=’ explist | 
		 functioncall | 
		 label | 
		 break | 
		 goto Name | 
		 do block end | 
		 while exp do block end | 
		 repeat block until exp | 
		 if exp then block {elseif exp then block} [else block] end | 
		 for Name ‘=’ exp ‘,’ exp [‘,’ exp] do block end | 
		 for namelist in explist do block end | 
		 function funcname funcbody | 
		 local function Name funcbody | 
		 local namelist [‘=’ explist] 

	retstat ::= return [explist] [‘;’]

	label ::= ‘::’ Name ‘::’

	funcname ::= Name {‘.’ Name} [‘:’ Name]

	varlist ::= var {‘,’ var}

	var ::=  Name | prefixexp ‘[’ exp ‘]’ | prefixexp ‘.’ Name 

	namelist ::= Name {‘,’ Name}

	explist ::= exp {‘,’ exp}

	exp ::=  nil | false | true | Number | String | ‘...’ | functiondef | 
		 prefixexp | tableconstructor | exp binop exp | unop exp 

	prefixexp ::= var | functioncall | ‘(’ exp ‘)’

	functioncall ::=  prefixexp args | prefixexp ‘:’ Name args 

	args ::=  ‘(’ [explist] ‘)’ | tableconstructor | String 

	functiondef ::= function funcbody

	funcbody ::= ‘(’ [parlist] ‘)’ block end

	parlist ::= namelist [‘,’ ‘...’] | ‘...’

	tableconstructor ::= ‘{’ [fieldlist] ‘}’

	fieldlist ::= field {fieldsep field} [fieldsep]

	field ::= ‘[’ exp ‘]’ ‘=’ exp | Name ‘=’ exp | exp

	fieldsep ::= ‘,’ | ‘;’

	binop ::= ‘+’ | ‘-’ | ‘*’ | ‘/’ | ‘^’ | ‘%’ | ‘..’ | 
		 ‘<’ | ‘<=’ | ‘>’ | ‘>=’ | ‘==’ | ‘~=’ | 
		 and | or

	unop ::= ‘-’ | not | ‘#’

以上的 Lua 語法中總有 23 個非終端項目,去除空行不算的話只有 40 行的 BNF 語法,而且高階語言該有的特性 Lua 都不會少,是一個非常完整的程式語言。

對於那些想學習「編譯器」與「設計程式語言」的程式人而言,我相信研究 Lua 會是一件很美好的事情,因為「簡單就是美」啊!

參考文獻

【本文由陳鍾誠取材並修改自 [維基百科],採用創作共用的 [姓名標示、相同方式分享] 授權】