FROM THE METRO-ORLANDO AUG (MOAUG) NEWSLETTER.
A SERIES of articles on LOGO by RICKI GERLACH.
 
We hope to distribute future parts of this series.




Ricki Gerlach's lst LOGO column from MOAUG:

               LEARNING WITH LOGO

                    PART 1

              BY: RICKI J. GERLACH



WHAT IS LOGO ?

  Logo has been described as being both a computer language and a
philosophy of learning. The major theme of Logo's philosophy is to
learn by doing, to learn by trial and error, to learn by exploring and
discovering. Errors do not reflect failure, but 'bugs' that can be
analyzed and fixed.
  The language itself was designed to reflect this philosophy by being
easy to use and powerful enough for sophisticated applications. Logo
achieves these two seemingly opposing goals by incorporating several
major design characteristics.
  The most important Logo feature is its ability to respond to new
user-created words or programs in the same way Logo responds to its
built-in words. Every computer language has certain 'reserved' words
that the computer knows and responds to. In Logo, these key words are
called PRIMITIVES, and include such commands as, MAKE, AND, IF,
REPEAT, FORWARD, and RIGHT. For example, the command

    FORWARD 50

will cause the turtle to draw a line 50 steps long on the screen,
while the command

    RIGHT 90

will turn the turtle 90 degrees to the right. We can create some
rather interesting programs using these primitives. Here is one of the
easiest programs to visualize.

TO BOX
REPEAT 4 [ FORWARD 50 RIGHT 90 ]
END

Remember to push SmartKey VI after typing this, so that ADAM will
store it in the memory, for later recall. Think of it as ADAM
remembering what BOX is. Now the key point here, is that we can run
this program, called a PROCEDURE in Logo, just by typing its name, the
same as we run a Logo primitive. We can even include this newly
defined procedure into other procedures. For example, here is a simple
procedure that uses our BOX procedure.

TO STAR
REPEAT 20 [ BOX RIGHT 18 ]
END
(SMART KEY VI)

Now just run STAR, and watch what happens.
  The primitive TO is used to enter the Logo editor in order to define
new 'vocabulary' words. When a language uses new words just like it
uses its built-in words, we say the language is 'extensible' and uses
the same 'syntax' for procedures as for primitives.
  Some words may be abbriviated, as
RIGHT  or RT       FORWARD or FD
LEFT   or LT       BACKWARD or BK
This means that the procedure you entered for BOX, could also be
entered as

TO BOX
REPEAT 4 [ FD 50 RT 90 ]
END
 
and the procedure for STAR could be entered as

TO STAR
REPEAT 20 [ BOX RT 18 ]
END

