I continue working on my JavaCC grammar for ECMAScript 5.1. It actually goes quite well, I think I've covered most of the expressions now.
I have now two questions, both of them are related to the automatic semicolon insertion (§7.9.1). This is one of them.
The specification defines the following production:
PostfixExpression :
LeftHandSideExpression
LeftHandSideExpression [no LineTerminator here] ++
LeftHandSideExpression [no LineTerminator here] --
How can I implement a reliable "no LineTerminator here" check?
For the record my LINE_TERMINATOR
is at the moment something like:
SPECIAL_TOKEN :
{
<LINE_TERMINATOR: <LF> | <CR> | <LS> | <PS> >
| < #LF: "\n" > /* Line Feed */
| < #CR: "\r" > /* Carriage Return */
| < #LS: "\u2028" > /* Line separator */
| < #PS: "\u2029" > /* Paragraph separator */
}
I have read about lexical states, but I am not sure if this is a right direction. I've checked a few other JavaScript grammars I have found, but did not find any similar rules there. (I actually feel myself a total cargo culter when I try to overtake something from these grammars.)
I'd be grateful for a pointer, a hint or just a keyword for the right search direction.
I think for the "restricted productions" you can do this
void PostfixExpression() :
{} {
LeftHandSideExpression()
(
LOOKAHEAD( "++", {getToken(0).beginLine == getToken(1).beginLine})
"++"
|
LOOKAHEAD( "--", {getToken(0).beginLine == getToken(1).beginLine})
"--"
|
{}
)
}