Exactly where is a RegularExpressionLiteral allowed?

Allen Wirfs-Brock Allen.Wirfs-Brock at microsoft.com
Mon Mar 23 11:36:40 PDT 2009

Pratap came up with an issue in reviewing the ES3.1 draft that I don't have a good answer to:

Sections 7 and 5.1.2 mention InputElementDiv and InputElementRegExp.
    7 "There are two goal symbols for the lexical grammar.  The InputElementDiv symbol is used in those syntactic grammar contexts where a division (/) or division-assignment (/=) operator is permitted.  The InputElementRegExp symbol is used in other syntactic grammar contexts."

Where in the grammar (or elsewhere) does it define **when** these two contexts are used?

There are no subsequent references to  InputElementDiv or InputElementRegExp in either the grammars or the prose of the specification.  Nor, is there any reference to RegularExpressionLiteral in the syntactic grammar or supporting prose.

So how am I as a language implementer reading this specification supposed to know that:
       var rx =  /a*z/;
is a valid expression whose RHS is an RegualrExpressionLiteral?  The best explanation  I can come up with for this interpretation solely from the specification is that the production to the right of the "=" in VariableDeclaration is an AssignmentExpression that can reduce to ConditionalExpression and since ConditionExpression doesn't describe any non-parenthesized expressions that begin with "/"  or "=/" I should use InputElementRegExp  and accept a RegularExpressionLiteral as a PrimaryExpression.  (and there really isn't anything in the specification that tells me to make that last leap.  Actually, I don't really think that the specification actually says that the above example is valid.)

This isn't a new ES3.1 problem.  Nothing has changed from the ES3 specification in this regard.  Am I missing something obvious?  Obviously this can't be unambiguously specified in the grammar but it sure seems like there should be some sort of comprehensible specification of exactly when RegularExpressionLiteral is allowed.


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