Re: [Help-jel] Variable argument list

[Mark Taylor]

Philip,

I don't have a solution to this problem, but I'd really like to be
able to use variable-length argument lists functions with JEL too.

In the "PLANNED FEATURES" section of the release notes for JEL 2.0.2
(http://www.gnu.org/software/jel/RELNOTES) it says:

   1. Allowing to call methods with variable number of arguments in JEL
   expressions.

which I think means it currently won't do that.  In case Konstatin
is listening: it would be great to see this in the (forseeable?)
future.

I'm a long time and extremely satisfied customer of JEL
(it forms the basis of the expression language in TOPCAT
http://www.star.bristol.ac.uk/~mbt/topcat/, widely used by
astronomers for analysis of catalogue data).  In case
Konstatin is listening again - many thanks for this excellent library.

Mark

On Mon, 7 Dec 2015, Philip Jonkergouw wrote:

> Hi,
> 
> I'm new to JEL and am considering using it for my project, so first of all, 
> thank you for creating it! Very impressive performance benchmarks (also 
> including my own tests).
> 
> I'm playing around in my home made JEL sandbox and have come across a problem 
> for which I would like to find a workaround. Consider this scenario:
> 
> public class Util {
> public static Object Decode(Object... b) {
> if (b.length < 2) throw new IllegalArgumentException("Too few arguments.");
> int i = 2;
> while (i < b.length) {
> if (b[0] == b[i-1]) return b[i];
> i += 2;
> }
> return null;
> }
> }
> 
> public class MySandBox {
> public static void main(java.lang.String[] args) throws Throwable {
> Object o = Util.Decode("Hello", "World", 2.0, "Hello", 3.0);
> System.out.println("decode(\"Hello\", \"World\", 2.0, \"Hello\", 3.0): " + 
> java.lang.String.valueOf(o));
> 
> Class[] stLib = new Class[1];
> stLib[0] = Util.class;
> gnu.jel.Library lib = new gnu.jel.Library(stLib,null,null,null,null);
> gnu.jel.CompiledExpression expr;
> expr = gnu.jel.Evaluator.compile("Decode(\"Hello\", \"World\", 2.0, 
> \"Hello\", 3.0)",lib, java.lang.Double.TYPE);
> };
> };
> 
> The error I get during execution is:
> 
> Exception in thread "main" gnu.jel.CompilationException: Function "Decode" 
> exists but parameters "Decode(class java.lang.String,class 
> java.lang.String,double,class java.lang.String,double)" can not be accepted 
> by it.
> 
> I can understand why this is happening.
> 
> However, might there be a way to disable this type of checking and "simply" 
> execute the code through the JEL library? Or could you suggest a workaround? 
> I realise there's nothing "simple" about the inner workings of JEL, please 
> don't get me wrong! The Java function "Decode" is meant to be extremely 
> flexible, passing any number and types of arguments. It can handle all sorts 
> of string comparisons, integer comparisons and return a number of types 
> including doubles, ints and strings. Creating strongly typed overrides isn't 
> an option.
> 
> Thanks in advance for the consideration.
> 
> Best regards,
> Phil

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
address@hidden +44-117-9288776  http://www.star.bris.ac.uk/~mbt/