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Eta (Haskell) and Neo4j

This is a repository combining examples from the neo4j website on stored procedures and user functions and from the Eta website on how to export Java functions written in Eta (Haskell).


To get things going you need eta (installation instructions), neo4j (website), Java 8 and maven.

Make sure you set JAVA_HOME to your Java 8 directory in wrapper/


If everything goes well it produces output.jar in the root directory of this repository. Copy that file to neo4j's plugins directory, for me that is /var/lib/neo4j/plugins. Restart neo4j and try out the example function fib.

neo4j-sh (?)$ return example.fib(12);
| example.fib(12) |
| 233             |
1 row
55 ms


  • Eta currently does not support annotations, so we need a Java wrapper library.
  • Make sure the Eta project is compiled as an executable, otherwise the Eta runtime won't be included and execution of the user function will fail with Failed to invoke function 'example.fib': Caused by: java.lang.NoClassDefFoundError: eta/runtime/stg/StgClosure.
  • Use a very simple local maven repository to store the produced jar file, this makes sure that it's included in the next jar file that gets included by neo4j.