[PD] [list] output

[Jonathan Wilkes]

--- On Thu, 2/4/10, ypatios <ypatios at gmail.com> wrote:

> From: ypatios <ypatios at gmail.com>
> Subject: Re: [PD] [list] output
> To: "Jonathan Wilkes" <jancsika at yahoo.com>
> Cc: pd-list at iem.at
> Date: Thursday, February 4, 2010, 6:31 PM
> hello
> 
> 
> 
> But as far as I can tell, [list] doesn't do any
> conversion at its outlet--
> 
> everything it outputs will have the selector
> "list", and it's up to other
> 
> objects like [route] to do any conversion they deem
> necessary.
> 
> 
> 
> For example, take the bug with sigbinops:
> 
> 
> 
>     [put anything you want in this message box(
> 
>     |
> 
>     [list]
> 
>     |
> 
> [+~ ]
> 
> 
> 
> error: inlet: expected 'signal' but got
> 'list'
> 
> 
> 
> 
> [1, 1 2, a, a b, a 2 b (
> |
> [list ]
> |
> [print ]
> 
> gives the following (0.42-5):
> 
> ######
> print: 1
> print: 1 2
> print: symbol a
> print: list a b
> print: list a 2 b
> 
> ######
> 
> so [list ] does some kind of conversion. what i don't
> understand is why there is no selector printed in the first
> two messages, where only numbers are present.

As far as your output from [print] goes:

For "1" and "1 2", they are an implicit float and implicit list, 
respectively.  This is a convenience feature of Pd: you don't have 
to type "float 1" every time you want to send a number from a msg box 
to a [+] object, for example.

For "list a b" and "list a 2 b", you would expect this because all 
non-list messages are converted to lists at the _inlets_ of the 
[list] object.

So that leaves "symbol a" unexplained: why isn't it "list a" if my 
theory is correct?  It's because the [print] object decided to print it 
that way: it receives a message "list a" and calls the print_list method, 
which decides to print "symbol a" instead of "list a".

Here's a trick that shows clearly what is happening in Pd 0.42-5, using 
the -n flag of [print], which suppresses the word "print":

[1(
|
[print]

[1(
|
[print -n]

For the first one, the print_method (x_interface.c) prints the 
word "print", followed by a colon, and the float itself.  For the second 
one, the word "print" is absent, so print_method then decides not to 
print a colon either. Only the float is printed.

However, consider the following:

[1(
|
[list]
|
[print -n]

Now the [print] calls the method print_list because the incoming message 
is a list.  How do I know this?  Because of a bug: instead of just 
printing the float-atom (as above), the output is ": 1", which matches the 
way print_list is telling Pd to format a list with at least one element 
that is not a symbol. [1]

Likewise, the output "symbol a" you referred to above enters [print] as 
"list a", and gets formatted as "symbol a" because it's a one-element 
list, with that element being a symbol-atom.

This is complicated by the fact that objects like [route] do a similar 
trick.

Ok, now I'm pretty convinced that [list] always outputs a list.

[1]- On older versions of Pd, you can still see a discrepancy if, for 
example, you compare the way [print] formats a gpointer, and a list 
containing one gpointer.

-Jonathan

> 
> anyways, you should provide [+~ ] operator with an argument
> if you want it to expect messsages instead of a signal
> (check help patch) :-)
> 
> 
> 
> ciao
> 
> -- 
> ypatios
> 
>