Hi,
the expressions module is just made for calculating scores, therefore
theres no need to call any function which takes strings. Also string
bindings are not consumed, it only supports DoubleValues as function
variables.
If you want a full scripting language, check Elasticsearch Expressions
(where I was also involved in development, especially the support for
lambdas and all kinds of dynnamic types). If you look at that code it is
a magnitude larger and more complex. This comes from the fact that
everything which is not a number in Java is a reference and therefor you
need invokedynamic to hell because you must be able to call methods on
object instances like String.
So I'd really say: expressions with reference types is a complete
rewrite, it could be a separate project, but rewriting a fully featured
Javascript compiler is slow on execution and has security risks. It was
already implemented by others. Making a more static language with
perfect support for safety and arbitrary invoke support based on
invokedyanmic and/or dynamic constants (like the Elasticsearch Painless
engine) is a very hard task. It took us months to implement it for
Elasticsearch in 2017. The ongoing port to Java 24 classfile library and
dynamic constants and hidden classes with classdata (Java 16) is still
not done (as far as I remember).
So I'd argue to keep expressions as a language to express score
canculations (plain function queries).
Small tip: If you want to provide a function to the engine that has a
fixed static "String" parameter or is bound to a fixed instance (because
it's virtual), you can register it as MethodHandle while binding it to
the String or another object instance, e.g., like a script function that
calls System.out.println(double) while returning Double.NaN as fake
return type:
functions.put("print",
MethodHandles.filterReturnValue(lookup.findVirtual(PrintStream.class, "println",
methodType(void.class, double.class)), MethodHandles.constant(double.class,
Double.NaN)).bindTo(System.out));
(I used this during debugging of expressions, mine was a bit of more
complex as it returned the double parameter itsself).
Uwe
Am 07.05.2025 um 20:55 schrieb David Smiley:
I've been looking at the Expressions module, a really impressive piece of
work!
The "JavaScript" sub-package only appears to support an extreme subset of
JavaScript, one where the only data type is a double. I don't see that it
supports Strings/text, to include passing Strings to methods and resolving
String data from a binding. Can someone confirm this? What would it take
to expand that?
I can see that Javascript.g4 (Antlr grammar) references a "STRING" but
can't make out if/how it's used in JavaScriptCompiler.
~ David Smiley
Apache Lucene/Solr Search Developer
http://www.linkedin.com/in/davidwsmiley
--
Uwe Schindler
Achterdiek 19, D-28357 Bremen
https://www.thetaphi.de
eMail:u...@thetaphi.de
