Third Brick Wall
steve_nunez at yahoo.com
Sat Jul 25 09:11:31 UTC 2020
Thanks Alan. What finally worked is:
(#"parallelize" *sc* (#"asList" 'Arrays (java:jarray-from-list '(1 2 3 4 5))))
But I can't help but think that going from a list to an array to a list is the long way 'round. Is there a better or more idiomatic way to do this?
More generally, I think much of the confusion is that a Lisper will enter into the FFI with a certain set of assumptions that don't hold. An array is a type of list? No Array class? Only specific types of array classes (e.g. array of Int)? I was hoping that this was or could be papered over in a manner similar to CFFI where I barely notice I'm using an external library most of the time.
On Saturday, July 25, 2020, 12:35:08 PM GMT+8, Alan Ruttenberg <alanruttenberg at gmail.com> wrote:
Try just using a java list. As I understand it, that should work the same way.
Since Java.util.List is abstract, you need to choose a concrete class, such as ArrayList.
(let ((jlist (jss::new 'arraylist))) (loop for el in '(1 2 3 4 5)
do (#"add" jlist el))
(print (jss::jlist-to-list jlist))
The print statement is to verify that we got what was expected, and to demonstrate jlist-to-list.
On Fri, Jul 24, 2020 at 10:21 PM Steven Nunez <steve_nunez at yahoo.com> wrote:
I think what parallelize really needs is a java.util.list. Alessio mentioned some reasons why an automatic conversion is challenging; perhaps a restart is easier? I.e. search for a method of the given name that takes a java.util.list, and if you're giving it an abcl.cons, the restart asks if you want an automatic conversion.
Trying such a conversion manually, it seems I need a jlist-from-list, but this doesn't exist in the JAVA package. How do I get a java.util.list from an abcl.cons ?
On Saturday, July 25, 2020, 5:20:30 AM GMT+8, Alan Ruttenberg <alanruttenberg at gmail.com> wrote:
If you send a smallish example of the code that doesn't work, and a list of the dependencies, I can have a look. I've been dealing with some stuff recently that might make it easier to debug.
You definitely can't use CopyToArray that way. You need to work with a java array(jarray-from-list '(1 2 3 4 5))Maybe:(#"parallelize" *sc* (jarray-from-list '(1 2 3 4 5)))
On Thu, Jul 23, 2020 at 11:03 PM Steven Nunez <steve_nunez at yahoo.com> wrote:
OK, I'm on lines 4 and 5 of 'hello world' and ran into yet another brick wall. Trying to convert the following two lines into ABCL:
List<Integer> data = Arrays.asList(1, 2, 3, 4, 5);
JavaRDD<Integer> distData = sc.parallelize(data);
it looks like it should be easy. Heck, I can do that in one line:
(#"parallelize" *sc* '(1 2 3 4 5)) ; *sc* defined yesterday and known to be correct
But no, it claims "no applicable method named parallelize found on JavaSparkContext" (but there is!). Reading through section 3.1.1 of the documentation, it appears that this is probably because '(1 2 3...) is a LispObject and not a Java object (why no automatic conversion?). Let's try to convert it:
(#"parallelize" *sc* (#"copytoArray" '(1 2 3 4 5)))
No instance method named copytoArray found for type org.armedbear.lisp.Cons'
And the same with using an array, e.g. (#"parallelize" *sc* (#"copytoArray" #(1 2 3 4 5)))
It's been a week and my intention was to have a working prototype by now and present ABCL as a viable alternative to use in a project. I haven't got past line 5 in 'hello world'. This doesn't bode well.
I've been reading about ABCL for years, and it's impressive. Full MOP, extensible sequences, nearly 100% ANSI compliance, and the ability to deploy on the JVM are major achievements. However, as a not-inexperienced Lisp programmer, I find the barrier to entry remarkably high and the documentation and examples sparse and insufficient to surmount the hurdles I encountered.
Please take these comments in the way they are intended: constructive feedback from someone who is a fan of the project and would love to be able to use it. It's nearly impossible to get Lisp introduced into enterprise environments, and ABCL provides a wedge into those types of projects, ticking the boxes on deployment and ability to work with legacy Java code. Perhaps it makes more sense to someone approaching Lisp from the Java side, but coming from the Lisp side to Java, there's a high barrier to entry. I know that no volunteer wants to write documentation, but more and clearer docs are sorely needed here. This is probably not news, but sometimes it helps to be reminded of the obvious.
I hate giving up, so this will be a personal background project in the hopes that at the next opportunity things will have improved to the point where we can consider introducing ABCL, so if anyone has any pointers, generally (though I think I would have found any docs or examples (lsw2) by now) and explaining this problem in particular, it would be greatly appreciated.
@easye, you mentioned your ember project. If you're going to continue with that, please message me. A Spark wrapper would be useful, serve as a good exemplar for using ABCL to wrap a large library and, with a companion tutorial, help others overcome the kind of obstacles I've encountered. I'd be happy to contribute.
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