JSR 308 and implicit n-ary lambdas
maurizio cimadamore
maurizio.cimadamore at oracle.com
Thu Nov 8 11:33:54 PST 2012
On 08-Nov-12 6:30 PM, Werner Dietl wrote:
> Thanks a lot for this patch!
>
> Is it safe for me to pull in the whole lambda/langtools repository or
> should I just selectively merge the JavacParser?
Better just to pull the parser alone.
Maurizio
>
> cu, WMD.
>
>
> On Thu, Nov 8, 2012 at 10:22 AM, Maurizio Cimadamore
> <maurizio.cimadamore at oracle.com
> <mailto:maurizio.cimadamore at oracle.com>> wrote:
>
> This patch passes all the tests I could throw at it :-)
>
> As I said before, it is based on the JavacParser available in the
> lambda branch; I believe now the differences between the lambda
> version and the JDK 8 version are few enough that you shouldn't
> have problems merging those changes in. In order to apply the
> patch you need first to update the parser code to match what's
> available in the lambda repository.
>
> With the patch, the parser now should apply a disambiguaton logic
> that is more 308-friendly (I hope!).
>
> Maurizio
>
>
> On 08/11/12 18:04, Maurizio Cimadamore wrote:
>>
>> Sorry, I gave you the wrong pointer - the new parser is here:
>>
>> http://hg.openjdk.java.net/lambda/lambda/langtools/file/tip/src/share/classes/com/sun/tools/javac/parser/JavacParser.java
>>
>> [in the lambda repository]
>>
>> This is slightly different (and more powerful) from the one in
>> JDK8/TL.
>>
>> I have a patch based on this parser code that should be helpful -
>> I'm currently testing it to see if it doesn't break anything ;-)
>>
>> I will send you the patch once testing is complete.
>>
>> Maurizio
>>
>> On 08/11/12 17:58, Werner Dietl wrote:
>>> Hi Maurizio,
>>>
>>> thanks for these clarifications!
>>>
>>>> One idea that comes to my mind would be to use the new lambda parser code
>>>> and, in the disambiguation logic, add some code for essentially skipping
>>>> through an annotation. I.e. an annotation should not cause the parser to
>>>> take one route over another - but it certainly restricts the set of
>>>> possibilities: i.e. either it's an explicit lambda, or an annotated cast. I
>>>> think that the new disambiguation code could work _provided_ that the whole
>>>> annotation is skipped before speculatively consuming the next token.
>>>>
>>>> [1] -
>>>> http://hg.openjdk.java.net/jdk8/tl/langtools/file/tip/src/share/classes/com/sun/tools/javac/parser/JavacParser.java
>>> I'm not sure what you mean with "new lambda parser code" and the
>>> earlier " lambda-repository [1]". I merged with jdk8/tl/langtools, so
>>> the parser in type-annotations should be based on the same code.
>>> Should I pull from some other repository to get a newer parser? Will
>>> this newer parser become the default in jdk8/jdk8?
>>>
>>> It would be great if you could spend some time in the type-annotations
>>> repository and see whether you can disambiguate the grammar. I think
>>> for you this should be a lot quicker than a day.
>>> If not, a pointer to what functions to look at would be helpful.
>>>
>>>
>>>> Also, we are adding support for intersection types in cast i.e.
>>>>
>>>> Object = (A & B)obj;
>>>>
>>>> Which probably further complicates things.
>>> I assume we also want to be able to annotate each sub-type, as in:
>>>
>>> Object o = (@TA1 A & @TA2 B) obj;
>>>
>>> Are there any other locations in the grammar where MONKEY_AT is now
>>> interpreted differently or where you think we might not have
>>> considered type annotations yet?
>>>
>>> Thanks!
>>> cu, WMD.
>>>
>>>
>>>
>>> On Thu, Nov 8, 2012 at 5:36 AM, Maurizio Cimadamore
>>> <maurizio.cimadamore at oracle.com> <mailto:maurizio.cimadamore at oracle.com> wrote:
>>>> On 08/11/12 10:14, Werner Dietl wrote:
>>>>
>>>> Lambda experts,
>>>>
>>>> the parser in file
>>>> langtools/src/share/classes/com/sun/tools/javac/parser/JavacParser.java
>>>> around line 968 contains the following:
>>>>
>>>> case LPAREN:
>>>> if (typeArgs == null && (mode & EXPR) != 0) {
>>>> if (peekToken(MONKEYS_AT) ||
>>>> peekToken(FINAL) ||
>>>> peekToken(RPAREN) ||
>>>> peekToken(IDENTIFIER, COMMA) ||
>>>> peekToken(IDENTIFIER, RPAREN, ARROW)) {
>>>> //implicit n-ary lambda
>>>> t = lambdaExpressionOrStatement(true,
>>>> peekToken(MONKEYS_AT) || peekToken(FINAL), pos);
>>>> break;
>>>> } else {
>>>>
>>>> this breaks in combination with type annotations on type casts.
>>>>
>>>> For an example failure, see this test case:
>>>>
>>>> http://buffalo.cs.washington.edu:8080/job/type-annotations-langtools/61/testReport/com.sun.tools.javac.annotations.typeAnnotations.classfile/TypeCasts/tools_javac_annotations_typeAnnotations_classfile_TypeCasts_java/
>>>>
>>>> In the above code, is the MONKEYS_AT used with the assumption that any
>>>> annotation after a LPAREN must be a declaration annotation on a parameter
>>>> and therefore a lambda should start?
>>>>
>>>> Your assumption is correct - currently the only way an @ could occur inside
>>>> a parenthesized expression is if a lambda parameter type was annotated; of
>>>> course I see this creates issues with type annotations. We could remove that
>>>> assumption from the parser, however note that a sequence of two identifiers
>>>> is also a trigger for an explicit lambda.
>>>>
>>>> Also you might want to look at the new parser code in the lambda-repository
>>>> [1], which has an explicit disambiguation logic; perhaps it would be easier
>>>> to make things work there by adding necessary rules for type annotations.
>>>>
>>>>
>>>>
>>>>
>>>> In the following code:
>>>>
>>>> String a0 = (@A String) o;
>>>>
>>>> instead of looking for just the MONKEYS_AT, I think we will have to parse a
>>>> whole type and then see whether we hit an identifier (it's a lambda) or a
>>>> closing RPAREN (it's an annotated cast).
>>>>
>>>> Do you see a simpler way to disambiguate this? Am I misunderstanding what's
>>>> happening here?
>>>>
>>>> One idea that comes to my mind would be to use the new lambda parser code
>>>> and, in the disambiguation logic, add some code for essentially skipping
>>>> through an annotation. I.e. an annotation should not cause the parser to
>>>> take one route over another - but it certainly restricts the set of
>>>> possibilities: i.e. either it's an explicit lambda, or an annotated cast. I
>>>> think that the new disambiguation code could work _provided_ that the whole
>>>> annotation is skipped before speculatively consuming the next token.
>>>>
>>>> Also, we are adding support for intersection types in cast i.e.
>>>>
>>>> Object = (A & B)obj;
>>>>
>>>> Which probably further complicates things.
>>>>
>>>> [1] -
>>>> http://hg.openjdk.java.net/jdk8/tl/langtools/file/tip/src/share/classes/com/sun/tools/javac/parser/JavacParser.java
>>>>
>>>> Maurizio
>>>>
>>>>
>>>> Thanks,
>>>> cu, WMD.
>>>>
>>>> --
>>>> http://www.google.com/profiles/wdietl
>>>>
>>>>
>>> --
>>> http://www.google.com/profiles/wdietl
>>
>
>
>
>
> --
> http://www.google.com/profiles/wdietl
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.openjdk.java.net/pipermail/type-annotations-dev/attachments/20121108/35e40313/attachment-0001.html
More information about the type-annotations-dev
mailing list