Re: Lua syntax ambiguity

The syntax is token based as far as I understand, so in t={[[[a]]]=true} it 
sees: punctuator {, string literal [[[a]], punctuator ], punctuator =, 
keyword true, and punctuator }. That does not meet the syntax so it is 
invalid.

On Sunday, August 16, 2026 at 10:25:12 AM UTC-4 Martin Eden wrote:

Ahoy list, 

Let's say we're writing Lua code generator. He just applies grammar rules. 

So let's take parts of Lua grammar and apply them. 

  chunk ::= block 

  block ::= {stat} [retstat] 

  stat ::= varlist ‘=’ explist 

  varlist ::= var {‘,’ var} 

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

  explist ::= exp {‘,’ exp} 

  exp ::=  false | true | LiteralString | prefixexp | tableconstructor 

  prefixexp ::= var 

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

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

  field ::= ‘[’ exp ‘]’ ‘=’ exp 

  fieldsep ::= ‘,’ | ‘;’ 

Problem is that "LiteralString" can start with "[" (long quotes). 
And so when writing index in "field" we emit "[", then we go 
to "exp" which may be "LiteralString" and we will emit another "[". 

So we'll have text like "t={[[[a]]]=true}". 

It's generated by perfectly abiding EBNF rules and greedy parser will 
miserably fail on it. 

I doubt there is a way to fix it by mangling EBNF grammar. 
That's just consequence that character to open index is "[", 
same character was chosen to start "long quotes", and table 
index can be literal string. 

-- Martin 

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