---
DROP ALIAS evals IF EXISTS;
CREATE ALIAS evals AS $$
import groovy.util.Eval;
@CODE
String evals(String aCode) throws Exception {
    Object o = Eval.me( aCode );
    if ( o != null ) { return o.toString(); }
    else { return (String) o; }
}
$$;

DROP ALIAS evald IF EXISTS;
CREATE ALIAS evald AS $$
import groovy.util.Eval;
@CODE
Double evald(String aCode) throws Exception {
    Object o = Eval.me( aCode );
    if ( o instanceof Double ) {
        return (Double) o ;
    } else {
       Object p = Eval.me( "o", o , "o as Double" );
       return (Double) p;
    }
}
$$;


---
assume main groovy jar is in classpath of h2 and jdk javac in PATH
use call or select e.g.