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Logo Programming Language
The Logo Programming Language, a dialect of Lisp, was designed
as a tool for learning. Its features - interactivity,
modularity, extensibility, flexibility of data types - follow
from this goal.
Although there are some versions of Logo that compile, it is
generally implemented as an interpreted language. The
interactivity of this approach provides the user with immediate
feedback on individual instructions, thus aiding in the
debugging and learning process. Error messages are descriptive.
For example
(The word fowad is not a primitive - one of Logo's
built in words - nor a procedure that you've defined.)
(Now that you've spelled it correctly, Logo knows the word forward,
but can't run your instruction because forward requires
additional information.
(Logo is happy. There's no error message. The turtle moves
forward 100 steps.)
Logo programs are usually collections of small procedures.
Generally, procedures are defined by writing them in a text
editor. The special word to is followed by the name of
the procedure. Subsequent lines form the procedure definition.
The word end signals that you're finished.
In our turtle graphics example
we defined a procedure to draw a square
to square
repeat 4 [forward 50 right 90]
end
to flower
repeat 36 [right 10 square]
end
Similarly, flower could be a building block of
something larger