parsing - LOOKAHEADs for the JavaScript/ECMAScript array literal production -

parsing - LOOKAHEADs for the JavaScript/ECMAScript array literal production -

i implementing javascript/ecmascript 5.1 parser javacc , have problems arrayliteral production.

arrayliteral : [ elision_opt ] [ elementlist ] [ elementlist , elision_opt ] elementlist : elision_opt assignmentexpression elementlist , elision_opt assignmentexpression elision : , elision ,

i have 3 questions, i'll inquire them 1 one.

this sec one.

i have simplified production next form:

arrayliteral: "[" ("," | assignmentexpression ",") * assignmentexpression ? "]"

please see first question on whether right or not:

how simplify javascript/ecmascript array literal production?

now have tried implement in javacc follows:

void arrayliteral() : { } { "[" ( "," | assignmentexpression() "," ) * ( assignmentexpression() ) ? "]" }

javacc complains ambiguous , or assignmentexpression (its contents). obviously, lookahead specification required. have spent lot of time trying figure lookaheads out, tried different things like

lookahead (assignmentexpression() ",") in (...)* lookahead (assignmentexpression() "]") in (...)?

and few other variations, not rid of javacc warning.

i fail understand why not work:

void arrayliteral() : { } { "[" ( lookahead ("," | assignmentexpression() ",") "," | assignmentexpression() "," ) * ( lookahead (assignmentexpression() "]") assignmentexpression() ) ? "]" }

ok, assignmentexpression() per se ambiguous, trailing "," or "]" in lookaheads should create clear of choices should taken - or mistaken here?

what right lookahead specification production like?

update

this did not work, unfortunately:

void arrayliteral() : { } { "[" ( "," | lookahead (assignmentexpression() ",") assignmentexpression() "," ) * ( assignmentexpression() ) ? "]" }

warning:

warning: selection conflict in (...)* build @ line 6, column 5. expansion nested within build , expansion next build have mutual prefixes, 1 of is: "function" consider using lookahead of 2 or more nested expansion.

line 6 ( before first lookahead. mutual prefix "function" 1 of possible starts of assignmentexpression.

here yet approach. has advantage of identifying commas indicate undefined elements without using semantic actions.

void arrayliteral() : {} { "[" morearrayliteral() } void morearrayliteral() : {} { "]" | "," /* undefined item */ morearrayliteral() | assignmentexpression() ( "]" | "," morearrayliteral() ) }

javascript parsing grammar ecmascript-5 javacc