I just had one of those eureka! moments when pondering the implementation of recursive calls.

I know that it does not take much effor to recurse a VI


But what about a vi that automates the process for you and wraps it up into a neat little sub-vi

here is my vision which I don't have time to complete but I belive that the community could easily wrap their wires around

Create a VI that when dropped into a BD will do the following

1. Create a sub-vi in the same location as the parent w/ some special namespacing
2. drop the necessary blocks for recursion: see picture above
3. determine the parents connector pane and set the sub-vi's pane to the same along w/ the static pane reference
4. Copy the parents icon and do a glyph edit to mark as recursive
5. then do a replace on the parents BD of the dropped recursion vi w/ the one just created

So I belive what would happen is the parent BD would have a sub-vi which looked almost identical which allowed for recursive calls!!!!

whatdaya think!!!

That's just crazy enough to work!

I'm thinking also that we could use express technology to accomplish this because it does the creation of a sub-vi for you w/out needing to make new files.

For those of you who are savvy to the express world. We have the ability to modify the source when running the configure vi. So when the express is configured (either automatically when dropped or when told so by the user) would be to modify the source VI to have the same inputs as the caller and drop the vi-server recursion fuctions in the guts.

oooooh I'm liking this.

Hey that sounds very interesting ! So you can create the correct connector pane constant ! I've been waiting for that for quite some time...
Can you create such a constant given a non-typed VI ref ?

Joris

I think an externalNode (XNode) will be better for that, because, as you modify the connector pane of the parent, the connector pane of the child (the recursive call subVI) should modify itself as well.

Edit: Another benefit is that you would not even need to create a SubVI in your project folder. The code would be right there behind the XNode.

PJM

Sounds great! Show me the code.

I like this idea!

Quick safety tip for all you who seek to peek under the skirts of LV: external nodes and XNodes are not the same thing, though they both serve the same goal. External nodes were LabVIEW R&D's first attempt at nodes that script themselves. They have issues and have been supplanted by XNodes, our second attempt. XNodes are better, in theory*.

*"In theory", from the Latin "en theos" meaning "with God" or, more specifically, "assuming He Who Built The System doesn't change His mind."

I would find it hard to beilve that w/ all the scripting tools out there that it would be impossible... although I have not specifically tried yet.

anyone.... Bueller?....Bueller??

Bueller here.
http://xnodes.lavag.org/externalnodes/recursion.html

I desire any and all feedback, this was a quick-as-possible venture that turned out to be quite nasty.

Source code is open for all of those curious, especially since the source code directly touts my abilities as a scripter.

Bonus features:

- Manual construction of a constant by typedef number array (that stupid ref is *not* an object creatable by the Create Object function!)
- Icon tweaking (a shadowed "R" -- which is fully customizable)
- Manual internal reconstruction upon double click (if necessary, which I don't think it should be)

Basically it's all that was talked about...just the code looks impossibly arbitrary because it took me a lot of trial and error to find out what LabVIEW would let me do.

Now if only I could convert this VI directly into



- Adam Rofer

Nice idea. I think your example of factorial might take a second look. Maybe I did something simply wrong, but I built your example, exactly as shown and it returns an answer of 0. Makes sense, you keep subtracting one each time, til you get to zero, then pass out the eventual zero result and multiply. What am I missing here?

One thing I've noticed is that frames sometimes don't refresh properly, so if you have a problem finding my previously referenced item (and you've been to my documentation site before) you can simply go here:

http://xnodes.lavag.org/externalnodes/recursion.html




I took the code directly from NI's example:
http://zone.ni.com/devzone/cda/epd/p/id/1827

Check a few things, like if your VI is re-entrant. That needs to be the case or else my recursion thingy won't do anything but send back the default values for whatever outputs.

- Adam Rofer

This post has been edited by AdamRofer: Jan 2 2008, 11:01 PM