Enums

[mitchellwrosen]

An example for how to bind to java enums would be great. I've tried several different things and none have worked out so far. For example, for some enum Day = MONDAY | TUESDAY | ... enum, this code:

type Day = J ('Class "foobar.Day")

dayMonday :: IO Day
dayMonday = [java| { foobar.Day.MONDAY } |]

seems to work (it compiles), and I also believe it can be underneath an unsafePerformIO, but regardless - actually trying to use this function throws

Exception in thread "main" java.lang.NoSuchMethodError: function_6989586621679038179
blah: JVMException (J 0x000000000208c638)

[mitchellwrosen]

Hm, I think my problem is due to an incorrect encoding of a java type. Specifically, I'm trying to encode a Enum BooleanClause.Occur as:

type JBooleanClauseOccur
  = J ('Class "org.apache.lucene.search.BooleanClause.Occur")

occurMust :: IO JBooleanClauseOccur
occurMust = [java| org.apache.lucene.search.BooleanClause.Occur.MUST |]

main :: IO Int32
main = withJVM [] $ do
  must <- occurMust
  [java| {
    System.out.println($must.toString());
    return 0;
  } |]

The generated java is:

public static java.lang.Object function_6989586621679038179 (org.apache.lucene.search.BooleanClause.Occur $must)
{                                                                                                                        
  System.out.println($must.toString());                                                                                  
  return 0;                                                                                                              
}

Note the name of the function is correct, so I assume it's being called at the wrong type somehow.

[mitchellwrosen]

I think part of the problem is that inner classes (like Occur) are written with an $ in the JNI, as org.apache.lucene.search.BooleanClause$Occur. However, this syntax doesn't work with the inline-java package, as in

type JBooleanClauseOccur
  = J ('Class "org.apache.lucene.search.BooleanClause$Occur")

because the type is dropped verbatim into the generated java module.

[facundominguez]

Nice finding!

[mitchellwrosen]

I'm happy to say I was able to stitch everything together using just the jni package and googling around for JNI syntax =)

[mitchellwrosen]

Here is the gist of it in case anyone else gets stuck, and I'm sure I missed some syntactic sugar in jvm or inline-java:

Get the BooleanClause.Occur class ID.

occur_class_id <- 
  findClass
    (referenceTypeName (SClass "org/apache/lucene/search/BooleanClause$Occur"))

Get the field ID of Occur.MUST.

must_field_id <-
  getStaticFieldID
    occur_class_id "MUST"
      (signature (SClass "org/apache/lucene/search/BooleanClause$Occur"))

Get the field from the class ID and field ID.

must_field <- getStaticObjectField occur_class_id must_field_id

Now time to make sure it works by calling the new BooleanClause(Query query, BooleanClause.Occur occur) constructor...

Get the BooleanClause class ID.

clause_class_id <-
  findClass
    (referenceTypeName (SClass "org/apache/lucene/search/BooleanClause"))

Some boilerplate for making some Query to pass as the first arg (code is unimportant).

query <- newTermQuery =<< newTerm "foo" "bar"

Call the constructor.

bclause <-
  newObject
    clause_class_id
    (methodSignature
      [ SomeSing (SClass "org/apache/lucene/search/Query")
      , SomeSing (SClass "org/apache/lucene/search/BooleanClause$Occur")
      ]
      SVoid)
    [ coerce query, coerce must_field ]

Make sure it doesn't blow up.

[java| {
  System.out.println($bclause.toString());
  return 0;
} |]

[mitchellwrosen]

I opened #50 to move some of this up from jni to the jvm level of abstraction, like call & callStatic.

[facundominguez]

Related #64. Duplicate?

[facundominguez]

This has been addressed in #90.