[PD-dev] proposed new "list" object

[Miller Puckette]

Hi devs...

I'm thinking about finally writing a "list" object for Pd to do jobs
like "append", "any", etc.  I've held off so far because I've felt
unsure about the best design... and once I stick it in the "base" Pd
it will be hard to change.

To avoid cluttering up the namespace I want to use just the one name,
"list", and use the first argument to differentiate between functions
(an idea inspired by Krzysztof's xeq object).  Here are the functions I
imagine:

    list append - append a list to another
    list prepend - prepend a list to another
    list cat - build a list by accumulating elements
    list serialize - spit out elements of a list one by one
    list first - output first n elements
    list last - output last n elements
    list length - output number of items in list
    list reverse - permute elements of a list back to front
    list pack - synonym for 'pack'
    list unpack - synonym for 'unpack'
    list selector - change selector of a list
    list <no args> - "prepend" the selector list to non-list messages

The "append" option would also play the role of "any" (just bang the left
inlet after putting any list in the right).

All of these would expect the "list" selector at the head of messages, with
the exception of plain "list"; all of them would output "list" messages except
"list selector".  These would work as follows:

--------------------------- list ----------------------------------
in (real message)   in (as printed)    out (real message)    out (as printed)
list                bang               (same)
list 1              1                  (same)
list foo            list foo           (same)
foo                 foo                list foo              list foo

--------------------------- list  selector bar -------------------------
in (real message)   in (as printed)    out (real message)    out (as printed)
list                bang               bar
list 1              1                  bar 1
list foo            list foo           bar foo
foo                 foo                (error)

There's one inconvenience with plain "list" since you can't differentiate
"list foo" from "foo" using its output; you'd have to use "route list symbol"
first and then do whatever you wanted to do differently ("list list foo" for
example).  It seemed better to leave that to the imagination of programmers,
since there seem to be disagreements about it...


cheers
Miller