Why is Python popular, while Lisp and Scheme aren't?

[Pascal Costanza]

Syver Enstad wrote:

> On another note, I think the Smalltalk method call (keyword message send)
> syntax is fabulously readable, why haven't anybody picked that up?
> Code like this is marvelously more understandable than the usual
> position based argument list that one uses in Lisp and C.
> 
> Ex: 
> 
> aCircle paintOn: aCanvas at: aPoint
> 
> Where aCircle, aCanvas and aPoint are variable names, and what is
> happening is that one is calling the method paintOn: at: where aCircle
> is self. The alternative:
> 
> aCircle.paint(aCanvas, aPoint)
> 
> is okay for this example but the smalltalk way lets you convey much
> more. Python has a kind of middle ground with its keyword messages,
> which is good but not quite as nice as Smalltalk.

In Common Lisp, you can have:

(paint circle :on canvas :at point)

Given that you have defined paint as follows:

(defun paint (&key on at)
    ...)

You can also have default values.

(defun paint (&key (on default-canvas) (at '(0 0)))
    ...)

So you can have all of the following.

(paint circle :on canvas)
(paint circle :at '(5 5))
(paint circle)

If you define circle to be a class, you can have the usual overriding of 
methods as follows:

(defmethod paint ((object circle)
                   &key (on default-canvas)
                        (at '(5 5)))
    ...)

(defmethod paint ((object rectangle)
                   &key (on default-canvas)
                        (at '(10 10))
    ...)

(paint (make-instance 'rectangle) :on my-canvas :at '(150 10))

...which is to show that you can mix positional and keyword parameters.

In the latter examples, circle and rectangle are classes defined as follows.

(defclass circle (graphical-object)
    (radius))

(defclass rectangle (graphical-object)
    (width height))

...where graphical-object is the common superclass, and radius, width 
and height are slots (instance variables).


etc., etc. ;)


Pascal

-- 
Given any rule, however ‘fundamental’ or ‘necessary’ for science, there 
are always circumstances when it is advisable not only to ignore the 
rule, but to adopt its opposite. - Paul Feyerabend