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#1577 — "This rule is recursively applied" rule is opaque

• bug_id: 1577
• creation_ts: 2013-07-08 09:30:00 -0700
• short_desc: "This rule is recursively applied" rule is opaque
• delta_ts: 2013-07-15 17:03:28 -0700
• product: Draft for 6th Edition
• component: editorial issue
• version: Rev 15: May 14, 2013 Draft
• rep_platform: All
• op_sys: All
• bug_status: RESOLVED
• resolution: FIXED
• priority: Normal
• bug_severity: enhancement
• everconfirmed: true
• reporter: Jason Orendorff
• assigned_to: Allen Wirfs-Brock

---

• commentid: 4353
• comment_count: 0
• who: Jason Orendorff
• bug_when: 2013-07-08 09:30:29 -0700

ES6 replaces the ES5 "early error" language with static semantics, a welcome change.

However, people seem to have trouble understanding the new rules about 'delete', especially the second rule. It says:

> * It is a Syntax Error if the derived UnaryExpression is
> PrimaryExpression : CoverParenthesisedExpressionAndArrowParameterList
> and derives a production that is used in place of UnaryExpression would
> produce a Syntax Error according to these rules. This rule is
> recursively applied.

https://people.mozilla.com/~jorendorff/es6-draft.html#sec-11.4.1

It means:

If `delete EXPR` is a syntax error, then so is `delete (EXPR)`.

Can the language be made clearer? Failing that, I think a NOTE is in order.

---

• commentid: 4354
• comment_count: 1
• who: Jason Orendorff
• bug_when: 2013-07-08 09:31:56 -0700

An example of an ES1-5 spec veteran not immediately grasping this rule occurs in the second paragraph of the comment here:

https://bugzilla.mozilla.org/show_bug.cgi?id=888002#c5

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• commentid: 4355
• comment_count: 2
• who: Jason Orendorff
• bug_when: 2013-07-08 09:35:35 -0700

I just noticed there's a typo in the rule.
"that is used" should be "that if used".

I don't think that is the main issue here though.

---

• commentid: 4356
• comment_count: 3
• who: Allen Wirfs-Brock
• bug_when: 2013-07-08 10:22:51 -0700

fixed in rev16 editor's draft

tweaked the language of the recursive application rule and added a clarify note in: 11.4.4, 11.13.3.1, 12.6.4.1

---

• commentid: 4413
• comment_count: 4
• who: Allen Wirfs-Brock
• bug_when: 2013-07-15 17:03:28 -0700

fixed in rev16 draft. July 15, 2013