module
10
A procedure you have defined is not fixed. You will want to change one - to make a shape bigger, or fix a number you got wrong - and typing the whole definition again is not the way.
ed "star
The screen clears and your procedure appears on it, with a line across the bottom:
Logo Editor:^C to accept,<ESC> to quit
That is a different kind of screen from the ? prompt. Nothing you type here
runs; you are changing text, and it takes effect when you leave.
Note the " before the name. That mark matters and S17 explains it properly;
for now, ed wants it.
Give it a moment. The editor takes a second to draw, and for that second you may see the status line with nothing above it.
The arrow keys do nothing in here. At the ? prompt they type [ and ];
in the editor they do neither that nor anything else. Moving about is done with
CONTROL.
| Press | What it does |
|---|---|
| CTRL-J | Down one line |
| CTRL-E | To the end of the line |
| CTRL-Y | Delete the character before the cursor |
| CTRL-C | Keep the changes and leave |
Typing inserts at the cursor. Nothing is ever overwritten, so to replace something you delete it first.
When the editor opens, the cursor is at the end of the first line - after the procedure's name.
There are about twenty more keys. Appendix I has the ones that are worth knowing; these four are enough for most changes.
to star
repeat 5 [fd 60 rt 144]
end
Type that in, then ss, cs, ht and star to see what it draws - a
five-pointed star.
Now change the 144 to 72:
ed "star144] - the closing bracket counts72]Starting from
A fresh boot, at the ? prompt.
What you should see
While you are in the editor, after the deletes and retyping, the second line reads:
repeat 5 [fd 60 rt 72]
CTRL-C prints star defined and takes you back to ?. Then cs and star
draws a pentagon.
The procedure is still called star, and now draws something that is not one.
Nothing stops you renaming it - the name is on the first line and you can edit
that too.
star.
Which shape do you get, and what does that tell you about when a change takes
effect?ed "star and press CTRL-C straight away, without touching anything.
What does Dr Logo say, and is it telling the truth?ed "wheel, which you have never defined. What appears? What does that
suggest about another way to write a procedure from scratch?| Symptom | Cause |
|---|---|
| The arrow keys do nothing | They do nothing in the editor. Use CTRL-H and CTRL-D to go left and right. |
Pressing [ gives you a bracket where you did not want one |
You are at the ? prompt, not in the editor. |
| The editor opens with nothing in it but the status line | Give it a second to draw. |
You get to wheel and end and nothing between |
That name has no procedure. ed offers you the frame for a new one. |
| Your change did not take | ESC throws changes away. CTRL-C keeps them. |
| You counted the deletes wrong and the number is odd | Delete the rest of it and type the whole number again - the editor always inserts, so half-deleted numbers stay put. |
ed "name opens a procedure for editing. The arrow keys do nothing; CTRL-J and
CTRL-E move, CTRL-Y deletes backwards, and typing inserts. CTRL-C keeps the
change, ESC throws it away. Appendix I has the rest of the keys.
S11, keeping your work - saving what you have written to the disc, so it is still there tomorrow.
