[IAEP] Turtles All The Way Down

C. Scott Ananian cscott at laptop.org
Tue May 24 13:11:29 EDT 2011

On Fri, May 20, 2011 at 11:09 AM, Alan Kay <alan.nemo at yahoo.com> wrote:
> Smalltalk actually got started by thinking about a way to make a child's
> Logo-like language with objects and pattern matching that could express its
> own operating system and environment.
> It is very tricky to retain/maintain readability (so the first Smalltalk was
> also an extensible language not just semantically but syntactically).
> With a tile language, this is really worth thinking about, since using tiles
> suggests ways to extend both the form and the meaning of the tiles.

I've written a follow-up post, musing on the "readability" aspect Alan
mentioned above:

Is it worth trading a very simple and direct syntax like:
  var Point = {};
  Point.x = 0;
  Point.y = 0;
  var Point3D = Object.create(Point);
  Point3D.z = 0;

for the more readable:

    Class("Point", {
        has: {
            x: {is: "ro"},
            y: {is: "rw"},

    Class("Point.ThreeD", {
        isa: Point,
        has: {
            z: {}

at the cost of introducing additional complexity into the object
creation process.  The complexity is in a library, so the base
language is kept small -- but it's still more turtles thrown onto the
stack that you have to understand.

Returning to Alan's point about tiles -- the nice thing is that you
could define a custom tile for the Class(....) syntax above, with
pretty selectors to help you select parent class, slot attributes,
etc.  But perhaps it's better just to keep the conceptual model small
-- then you don't need fancy GUI widgets to help you out.

For a more concrete example, you might want to read through:

starting at line 333 or so.  That's a widget library written in
Simplified JavaScript/TurtleScript which uses prototype inheritance
extensively.  You can do clever things like swipe the implementation
of a function from a totally different class; see how we do "multiple
inheritance" around line 661.  Is the Joose syntax an improvement?

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