Java Platform Module System

[Remi Forax]

It's context-free because a context free grammar defined its input in term of terminals and the theory do not say how to map a token to a terminal.

Jay is right that it requires to use either some specific parser generator like Tatoo [1] the one i've written 10 years ago (because i wanted the tool to help me to extend a grammar easily) or to modify an existing parser generator so the parser can send the production state to the lexer which will enable/disable the automata that recognize the associated keywords .

Rémi

[1] http://dl.acm.org/citation.cfm?id=1168057

----- Mail original -----
> De: "Alex Buckley" <alex.buckley at oracle.com>
> À: "Jayaprakash Arthanareeswaran" <jarthana at in.ibm.com>, "Dan Smith" <daniel.smith at oracle.com>, "Brian Goetz"
> <Brian.Goetz at oracle.com>
> Cc: jigsaw-dev at openjdk.java.net
> Envoyé: Mercredi 3 Mai 2017 19:46:54
> Objet: Re: Java Platform Module System

> On 5/2/2017 3:39 PM, Alex Buckley wrote:
>> On 5/2/2017 7:07 AM, Jayaprakash Arthanareeswaran wrote:
>>> Chapter 2 in [1] describes context-free grammars. The addition to "3.9
>>> Keywords" defines "restricted keywords", which prevent the grammar for
>>> ModuleDeclaration from being context-free. This prevents compilers from
>>> using common parser generators, since those typically only support
>>> context-free grammars. The lexical/syntactic grammar split defined in
>>> chapter 2 is not of much use for actual implementations of
>>> module-info.java parsers.
>>> The spec at least needs to point out that the given grammar for
>>> ModuleDeclaration is not actually context-free.
>>
>> The syntactic grammar in JLS8 was not context-free either; the opening
>> line of Chapter 2 has been false for years. For JLS9, I will remove the
>> claim that the lexical and syntactic grammars are context-free, and
>> perhaps a future JLS can discuss the difficulties in parsing the
> 
> Jan Lahoda pointed out privately that the syntactic grammar in JLS8 and
> JLS9 is in fact context-free -- it's just not LL(1). Not being LL(1) is
> what I should have said the grammar hasn't been for a long time.
> 
> Alex