JSR 308 and implicit n-ary lambdas
Werner Dietl
wdietl at gmail.com
Thu Nov 8 10:30:27 PST 2012
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?
cu, WMD.
On Thu, Nov 8, 2012 at 10:22 AM, Maurizio Cimadamore <
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> <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
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