Create a Custom Gremlin Step in Any JVM Language?

[James Thornton]

During my experimentation in creating Gremlin user-defined steps (https://github.com/tinkerpop/gremlin/wiki/User-Defined-Steps), I had a thought -- what if you could create a Gremlin step using any JVM language?

To create a step in Gremlin you write a closure in Groovy and include it as the third argument to the Gremlin.defineStep() method:

  Gremlin.defineStep("myCustomStep", [Vertex,Pipe], myCustomClosure)  

A few weeks ago Marko refactored Gremlin by pushing much of the heavy lifting down into Pipes, and this opens up the doors for Gremlin implementations in other JVM languages (https://groups.google.com/d/msg/gremlin-users/5DiHC9dWSAA/cWDZFnBl9l4J). 

But what if instead of rewriting all of Gremlin, you were able to just write your custom steps in whatever JVM language you want?

I did a few Google queries, and it looks like you can create Groovy closures in other JVM languages. Here's a blog about someone creating a Groovy closure in Java (http://www.jroller.com/melix/entry/coding_a_groovy_closure_in). 

I am not a JVM expert so I don't yet know if you can do this for every language, but it would be way cool if you could.

Hopefully some of the JVM gurus around here can provide more insight.

- James

[James Thornton]

Here's the key line and the docs to Groovy's MethodClosure function...

  MethodClosure cl = new MethodClosure(MyJavaClass.class, "staticMethod");

http://groovy.codehaus.org/api/org/codehaus/groovy/runtime/MethodClosure.html

- James

[Daniel Quest]

Yep would be awesome

Sent from my iPod

[James Thornton]

> But what if instead of rewriting all of Gremlin, you were able to just write your custom steps in whatever JVM language you want?

Well after some hacking, I got this to work. Evidently it is possible to write Jython methods that compile down to Gremlin closures -- I presume this will for other JVM languages too.

I'll post a tutorial soon.

- James  

[James Thornton]

Ok, I created a library that provides an example for how to write custom, user-defined Gremlin steps in Jython. 

The library is called mogwai, and it's on Github (https://github.com/espeed/mogwai).

You should be able to adapt it for any JVM language. 

Here's the example code:

Jython module:

https://github.com/espeed/mogwai/blob/master/mogwai/steps/jython/Gizmo.py

Java Interface:

https://github.com/espeed/mogwai/blob/master/mogwai/interfaces/GizmoType.java

Java Factory you can reuse for each Jython module:

https://github.com/espeed/mogwai/blob/master/mogwai/factories/JythonFactory.java

Groovy script that create the Gremlin steps:

https://github.com/espeed/mogwai/blob/master/examples/gizmo.groovy

Instructions on how to make this work:

https://github.com/espeed/mogwai/blob/master/README

- James

[Pierre De Wilde]

Cool. Thanks for sharing.

Pierre