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#297 — Undecidable tokenization in modules' grammar

• bug_id: 297
• creation_ts: 2012-03-09 07:06:00 -0800
• short_desc: Undecidable tokenization in modules' grammar
• delta_ts: 2013-10-10 12:35:14 -0700
• product: Harmony
• component: proposals
• version: unspecified
• rep_platform: All
• op_sys: All
• bug_status: RESOLVED
• resolution: INVALID
• priority: Normal
• bug_severity: major
• everconfirmed: false
• reporter: Xavier Cambar
• assigned_to: Allen Wirfs-Brock
• cc: ["dherman", "samth", "xcambar"]

---

• commentid: 738
• comment_count: 0
• who: Xavier Cambar
• bug_when: 2012-03-09 07:06:26 -0800

Consider the following expression:

export x, y, z;

According to the grammar defined in the harmony:modules wiki page, this expression can have two tokenized forms:

ExportDeclaration
-> ExportSpecifierSet
-> Id
-> Id
-> Id

ExportDeclaration
-> ExportSpecifierSet
-> Id
-> ExportSpecifierSet
-> Id
-> ExportSpecifierSet
-> Id

A parser has no way of choosing one form or the other unless maybe by using operator precedence, which is not defined in the grammar.

I've posted a possible revised grammar here: https://gist.github.com/1990115, replacing

ExportSpecifierSet ::= "{" ExportSpecifier ("," ExportSpecifier)* "}"
| Id ("," Id)*
| "*" ("from" Path)?

with

ExportSpecifierSet ::= "{" ExportSpecifier ("," ExportSpecifier)* "}"
| Id
| "*" ("from" Path)?


Regards.

---

• commentid: 5887
• comment_count: 1
• who: Allen Wirfs-Brock
• bug_when: 2013-10-10 12:35:14 -0700

no longer applicable to current ES6 module grammar