[PD] Implementing a scheme extension language

Larry Troxler lt at westnet.com
Mon Jun 25 00:20:41 CEST 2001

pix at test.at wrote:
> i have been thinking about something like this for a while too. i have
> settled on a different approach to the problem (which essentially involves
> making a separate, more scheme-savvy pd-like application), because my time
> is not as limited (i am looking at it as a -really- long term project).
> but as a quick way of getting a lot of extra functionality into pd, the
> mechanism you described would be cool.
> my halfbaked inital conception of something like what you have describe
> was that there would be an object which takes the name of a textfile,
> which contains scheme code to build the object. kind of like providing a
> mechanism for describing abstractions in scheme.
> eg "scheme myobject.scm"..
> internally tho, i think the execution model of pd is going to make this
> tricker than it appears (hence my desire to ambitiously rebuild pd from
> the
> gorund up).
> pix.

Hi pix - 

I pretty much have SIOD working with PD. But of course, it is slow.
Especially because for now, I have not attempted to interface the data
structures but instead create strings containing the expression to be
evaluated in scheme, and similarly parse the string that is returned.

I had embarked on this in the hopes of having a faster way of creating
objects without having to compile C code and understanding the PD API,
but of course, in doing this, I personally have learned enough about the
PD functions that it might now be just as fast to code my externs in C!

Once I iron out a few details, I hope to post the code. It works
similarly to what we both have been describing, except that I load a
single scheme file into the interpreter which defines all the objects.
the PD object names a function in scheme which creates a closure for the

> On Sat, 28 Apr 2001, Larry Troxler wrote:
> > Hi all,
> >
> > I am attempting to implement an library which will provide a scheme
> > extension language, and would welcome any comments.
> >
> > First I should say what my motivation is. I have found PD very fun and
> > practical, except where any kind of serious programming logic is needed.
> > In these cases, I have found it a mind bender to try to implement
> > graphically what could be accomplished very easily using a text-oriented
> > language. As a case in point, I want to create a PD piano instrument
> > that uses a piano sample CD. Although I got it working with a particular
> > set of sample files, it is clear that the graphical hookup technique is
> > certainly not a sensible way to go about this. As a result (well, not
> > only because of this, but also because of several other similar
> > situations), I have longed to drop down into a textual language to
> > implement PD objects.
> >
> > True, I could use C and implement what I need directly as a loadable
> > object, but I though that an interpreted language would be in general
> > nicer, and fast enough, for most purposes like this.
> >
> > I have decided at first to use "scheme in one defun" (siod), simply
> > because my time is limited, and siod it takes much less brain power to
> > integrate siod, then to learn how to implement guile or elk.
> > Of course, guile/elk is more complete and probably will run a lot
> > faster, and this is a future option.
> >
> > I'd like to present my first-attempt specs for how this would work, and
> > see if anyone has any comments. This is very rough-draft and not
> > precise, but just to give a general idea...
> >
> > 1) implement a global receiver (like "pd"), that when it receives any
> > message, sends it to the sheme interpreter to evaluate. This would not
> > be as nice as a seperate interpreter console, but for now, it will avoid
> > me to have to deal with a new gui for an interpreter. Question: what to
> > name this? I will take "scm" for now, so that for example, in a message
> > box, "; scm foo `( 1 2)" will call the scheme function "foo" with the
> > list (1 2) as an argument. The outer pair of parenthesis is implicitly
> > added.
> >
> > 2) The scheme function (pdsend 'receiver arg1 arg2 ..) will send its
> > args to the pd receiver named "receiver". For example, (pdsend 'pd
> > 'quit).
> >
> >
> > 3) The scheme function (pdreceive 'x fn) will create a pd receiver, so
> > that when pd sends a message to "x", the scheme function "fn" will be
> > called, and passed the message as a list.
> >
> > 4) The pd object "scmob" (Question: better name?) will instantiate a pd
> > object implemented in scheme (for now I won't deal with DSP signals).
> > Its first argument, prepended with "make-", will be the name of a scheme
> > function which will create a closure which will become the object. The
> > number of inlets to this object will be determined by the number of the
> > arguments in the lambda expression returned by the generation function.
> > And the number of outlets will be determined by, well I don't know yet.
> > The additional creation arguments will be passed to the creation
> > function. Within the lambda, the function (pdout n val) would send val
> > to the n'th outlet of the object. When anything is received at the first
> > inlet to the object, the arguments of the lambda will be bound to the
> > current values at the inlets, and the lambda will be called.
> >
> > For example, say we have in the scheme environment (note, I just typed
> > this in without a proper editor, so there could be paren mismatches,
> > etc, but to give the general idea...) :
> >
> > (define (make-integrator initial-value)
> >   (let ((current initial-value))
> >     (lambda (x)
> >        (cond
> >          ((and (symbol? x) (eq x 'reset))
> >             (set! current initial-value))
> >          ((number? x)
> >              (set! current (+ current x))))
> >        (pdout 0 current)
> >        (pdout 1 x)))
> >
> >
> > Given that the above has been evaluated in the scheme environment, then
> > typing "scmob integrator 10" into a PD object would create a an object
> > with one inlet, whose first  outlet would be a sum of the number object
> > received at the inlet, or be reset to 10 if the "reset" message is
> > received at the inlet. The second outlet would be a copy of the inlet.
> >
> > --
> >
> > Larry Troxler
> >

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