Why Logo?

Or, why Logo instead of Python?

• Most people don't need the skills to become professional programmers.
• Especially when they are 9 years old
• We shouldn't confuse our ideas about programming with the education goals of programming. This includes many of the programming practices we use for software: thoughtful naming, object-oriented programming, modularity, etc.
• People who think we should teach children assembly language are just crazy.

How Logo is different from Python

• It doesn't put effort into code reuse.
• Commands can be abbreviated, and can be very short (like FD for forward) because children type very, very slowly.
• Very little punctuation.
• Structure is casual with respect to command separation and whitespace. Also case-insensitive.
• It uses dynamic scoping.

Examples

In Logo:

? REPEAT 4 [FD 100 RT 90]
? PR [Hello world!]
Hello world!

The Python equivalent:

>>> from turtle import *
>>> for i in range(4):
...     forward(100)
...     right(90)
>>> print 'Hello world!'
Hello world!

What's neat about PyLogo

• It's free, of course (and cross-platform and everything else you get from implementing it in Python -- the only other decent implementations of Logo on Linux are UCBLogo and TurtleTracks)
• It's traditional Logo (lots of naive non-traditional implementations of logo exist, but they often just implement turtle graphics and ignore the rest)
• It integrates well with Python.

Python Integration

• All Python functions are made easily available.
• Procedures can be easily annotated with function attributes, allowing renaming, or allowing access to the Logo interpreter object.

Making a procedure available is easy:

# in turtle.py...
from turtle import forward
forward.aliases = ['fd']

; In logo...
? import "turtle
? FD 100

Even control structures are easy:

def logoWhile(interp, test, block):
    lastVal = None
    try:
        while logoEval(interp, test):
            try:
                lastVal = logoEval(interp, block)
            except LogoContinue:
                pass
    except LogoBreak:
        lastVal = None
        pass
    return lastVal
logoWhile.logoAware = 1
logoWhile.logoName = 'while'

This is the actual implementation of WHILE in Logo.

Why you might want to work on PyLogo

• Python has a bunch of libraries that would be nice to make available to a Logo user, either directly or indirectly.
• The PyLogo interpreter is really easy to play with (Logo is a very simple language).
• Logo is a real Lisp language. It's simple and regular, and perhaps a bit antiquated (particularly dynamic scoping), but it's still a real language.
• Unfortunately, I get really distracted with different projects, so I haven't been able to keep moving it forward.
• Also, I'm not very experienced with GUI programming, and a Logo environment should have a good interface. PyLogo doesn't have one.
• But PyLogo has almost no professional potential, so it's just plain fun, and you can ignore all other aspects.
• Writing languages is fun. But hard. Playing around with a toy language is educational, but ultimately not useful for anyone else.
• But Logo is a toy language that isn't just a toy.
• Reminder: http://pylogo.org
• If you want to look at it, please drop me a note -- the code in the repository may not be in the best shape at the moment.