Java Platform Module System

Alex Buckley alex.buckley at
Wed May 3 17:46:54 UTC 2017

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
>> 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.


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