[jira] [Commented] (FLINK-3414) Add Scala API for CEP's pattern definition

["Dawid Wysakowicz (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-3414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16062863#comment-16062863 ] 

Dawid Wysakowicz commented on FLINK-3414:
-----------------------------------------

Hi [~kkl0u], [~dian.fu]

As there is ongoing work to introduce GroupPatterns( [FLINK-6927] ) and branching patterns ( [FLINK-4641] ) I would like to start a discussion about reworking our Pattern API as a better hierarchical API would help in the implementation.

I feel there is couple of problems with current API:
# there is lots of places where we throw {{MalformedPatternException}}, it would be better to restrict illegal patterns in API rather than throw exceptions in runtime
# API does not corresponds well to hierarchy of groups and branches
# it is hard to provide a good intuitive Scala dsl
 
In my branch [cep-api-rebuilt| https://github.com/dawidwys/flink/tree/cep-api-rebuilt ] in {{flink-cep-scala}} in package {{org.apache.flink.cep.scala.pattern.proto}} I created a proposal for a new API written in Scala(better type support I think). For this API to work we would need to port {{NFACompiler.java}} into the new API, which I think should be done also in Scala, what would allow us to better leverage scala type support by pattern matching.

As the current API is not annotated as Public, I feel there is no that much of a problem with breaking API compatibility. 

I would love to hear your opinions.
 

> Add Scala API for CEP's pattern definition
> ------------------------------------------
>
>                 Key: FLINK-3414
>                 URL: https://issues.apache.org/jira/browse/FLINK-3414
>             Project: Flink
>          Issue Type: Improvement
>          Components: CEP
>    Affects Versions: 1.0.0
>            Reporter: Till Rohrmann
>            Assignee: Dawid Wysakowicz
>            Priority: Minor
>
> Currently, the CEP library only supports a Java API to specify complex event patterns. In order to make it a bit less verbose for Scala users, it would be nice to also add a Scala API for the CEP library. 
> A Scala API would also allow to pass Scala's anonymous functions as filter conditions or as a select function, for example, or to use partial functions to distinguish between different events.
> Furthermore, the Scala API could be designed to feel a bit more like a DSL:
> {code}
> begin "start" where _.id >= 42 -> "middle_1" as classOf[Subclass] || "middle_2" where _.name equals "foobar" -> "end" where x => x.id <= x.volume
> {code}



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