[PD] confused about $1 in messages

[Jonathan Wilkes]

I'm not sure why the people replying to you are feigning ignorance on how this situation could possibly be confusing.  You're chopping off the word "one" with [list split] and leaving it intact on the other message; yet the dollarsign substitution gives you the same output in both cases.  Furthermore, if you use [list length] on each message you will find the two message have a different number of elements.

What you don't see, however, is that [list] objects like [list split] interpret incoming messages as "list" messages-- that is, they add the word "list" to the beginning of the message.  Also, they prepend a "list" selector to the messages they send out (except for [list trim], of course).

But we're not done.  The selectors "list", "float", and "symbol" are special and do not get counted as elements with [list length].  Yet inside message boxes they _do_ get counted as the selector (i.e., the very first symbol atom in a message) when variable substitution is involved.

Once you know those two details it gets a little easier to grasp.

This is all further complicated by the fact that there is no dollarsign variable in Pd that can get the selector of an incoming message.  So for "list two three" you can't get "list" with a dollarsign variable, and likewise for "one two three" you can't get "one" with a dollarsign variable.  That's a real sticking point for new users, especially because they've no doubt already seen how seamlessly everything works when only numbers are involved.

So I'd suggest everyone have a look at the help patch for [list], especially the subpatch labeled [pd about-lists].  In it, Miller Puckette-- the guy who designed and implemented this part of the language-- describes what is happening in some detail.  In his explanation he questions his own design, even going so far as calling the very distinction you point out here "ugly".  It's not the easiest part of Pd to understand, and it's the reason why you're having a problem in the patch example you gave.

But if you learn to use the [list] family objects when dealing with data messages it can makes things a lot easier.  Since you know those objects will output messages with a "list" selector, then for everything other than a bang you're guaranteed that [$1( will work properly.

-Jonathan




On Monday, January 20, 2014 11:33 AM, Jack <jack at rybn.org> wrote:
 
Le 20/01/2014 15:34, rolfm at dds.nl a écrit :
> dear list,
>
> i'm confused about the $1 replacement in messages.
>
> [one two three(
> |\
> | \
> |  [list split 1]
> |      /
> |     /
> |    /
> |   /
> |
> [;
> [this $1 $2(
>
> [r this]
> |
> [print this]
>
> output:
> this: two three
> this: two three
>
> why?
>
> rolf
>
>
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[one two three( is not a list.
[list one two three( is a list.
So what you get is *maybe* the normal behavior ?
But, yep, what did you expect ?
++

Jack




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