Home » Archimedes archive » Archimedes World » AW-1993-05.adf » AWMay93 » !AWMay93/Goodies/LogoV2/Technical/ASCII
!AWMay93/Goodies/LogoV2/Technical/ASCII
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Archimedes archive » Archimedes World » AW-1993-05.adf » AWMay93 |
| Filename: | !AWMay93/Goodies/LogoV2/Technical/ASCII |
| Read OK: | ✔ |
| File size: | 24ED bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
The logo interpreter By Duncan F. McPherson
Technical Details
Welcome to logo V2.0 � Archimedes World 1993
My logo interpreter is now finished, and amongst many new
features, it now offers the ability to save your logo program`s
output as a sprite file or a draw file (so you can have logo
generated lineart in your DTP documents e.t.c.).The interpreter
supports loops, subroutines, command abbreviations and
expressions (though not variables).All the usual logo commands
are there as well, making graphics programming childsplay (even
for big kids!).
Driving a buggy
The robot driver program also comes with a fully working
driver program, in its application directory (under the filename
2Motors).This driver works with an Acorn User port expansion card
(on my A3000) to drive my simple home made buggy (Made from plans
in the Usborne book ROBOTICS).I have designed my !Robot
application so anyone can easily rewrite the basic library file
"Driver" with their own code to drive any buggy under the
sun.This system also allows for pleanty of future expansion.
See the REM lines in the basic file 2Motots for more details
Entering Programs
To create a logo program you need to use a text editor such as
edit or 1st word plus (in non wp mode).Once you have finished
typing in your program check it over thoroughly, and make sure
that every statement in the program is separated by either a a
new-line code (&0D) or a `:` character.Statements that haven`t
been separated properly will generate errors when you try to run
your program in the interpreter.
The logo command line
The command line window inside the logo application can be
used to execute subroutines (by typing their names) or any normal
logo command.Note that you cannot define TO subroutines at the
command line, this can only be done using a textfile program.The
program searches the currently loaded program for any name you
type that it does not recognise as one of it`s own commands, only
throwing back an error if no TO subroutine can be found going by
that name
Any normal logo command can be used at the command line
(forward,back,left e.t.c.), as well as loops and TO subroutine
names.Commands are separated as usual by the `:` character
The HELP function
The help function is supported as a window available by
clicking on `HELP` in the programs menu tree or by typing HELP
followed by the logo command you would like help on.
Program execution
Because the logo interpreter was written in BASIC, execution
is not as fast as it might be.Also the wimp environment slows
down programs, as extensive redrawing of the interpreters display
window is necessary every time the turtle is moved or a line is
drawn.To help speed up the programs execution, close the programs
display and command line windows leaving the program status
window open only, to indicate programs progression.
Loops
The interpreter uses a stack system to keep track of current
loops so you can nest loops at the command line or inside your
programs.
The structure of a loop is as follows :
[<number of times to execute the loop> <== start of loop
FORWARD 100
RIGHT 90 <== statements
e.t.c.
] <== end of loop
Try the following at the command line:
[24:Forward 50:Right 15:]
This short statement draws a circle by repeating the
statements forward 100 and right 15 twenty four times.
The looping system provided is a powerful feature of the
interpreter, and can be used to repeat any logo command or
commands several times.
`To` subroutines
The interpreter has provisions for subroutines via the TO and
EndTo commands.A subroutine takes the format as follows :
TO <name of routine> <== start defining the subroutine <name>
FORWARD 100
RIGHT 90 <== statements
ENDTO <== Tells logo that`s the end of the
subroutine
The subroutine can then be executed at either the command
line or inside the program by typing its name only.
Note subroutines cannot be defined at the command line.
The FINISH command
This command stops the execution of the program currently
running.It is needed to prevent the interpreter carrying on as it
normally would to the end of a program, when a program contains
one or more TO subroutine definitions, as if the interpreter
tries to execute these sequentially an error will be generated.
The Error messages
The interpreter generates the following error messages which
are displayed in its command line window :
Bad logo parameter
No such subroutine
Too many TO subroutines
Not in a TO subroutine
These messages reflect an error in either the users program or
the statement just typed in at the command line window.
Background Execution
Execution of logo programs takes place in the background (via
the wimp`s null reason code), but statements at the command line
take over the machine during their execution.This is not normally
noticeable unless you have entered commands which will take some
time to execute at the command line.To stop a command during its
execution at the command line hit the escape key a few times
Running Programs
Programs can be run by either typing `RUN` at the logo command
line or by clicking on RUN in the program status window.This
window can be displayed by clicking on the `program` option in
the interpreters main menu tree, though this should not normally
be necessary, as the interpreter brings up the status window as
soon as a program is loaded.
Overheads
Every time a logo command which moves the turtle is executed,
the interpreter broadcasts a message over the wimp message system
describing the command just executed.This message will normally
be intercepted by a robot driver program which will in turn move
a turtle around.The format of this message is as follows :
Wimp poll code 17 (user message)
message_block!16=&4C4F474F ("LOGO" in ASCII")
message_block!20=command number
message_block+24=numeric string containing a parameter
to go with the command.
The command numbers are as follows :
1. Forward (the parameter is the distance)
2. Back (the parameter is the distance)
3. Left (the parameter is the angle in degrees)
4. Right (the parameter is the angle in degrees)
5. Penup (no parameter)
6. PenDown (no parameter)
7. PenColour (the parameter is the colour 0-16)
Using this messages the application !Robot will be able to
drive floor turtles via a logo program or commands at the logo
command line.Presently the !Robot program only displays messages
received in its windows, but I have left it easily alterable
(just fill in the blank procedures) so that I can make it drive
various buggy`s and floor turtles at a later data.
Comments inserted into programs
You can insert any comment you like in your ASCII text
program file after a `/` command.This command behaves just like
BASIC`s REM command.
Remember that after your comment still put in a `:` character
or a return code, to separate it from the next statement.The same
goes for the statement before your comment.
The basic logo commands
Forward <distance> Moves your turtle forward the distance
specified by you in the parameter following it.
Back <distance> Moves the turtle back <distance> units
Left <angle> Turns the turtle anti-clockwise through <angle>
degrees
Right <angle> Turns the turtle clockwise through <angle> degrees
PenUp Tells the interpreter not to draw lines
PenDown Tells the interpreter to draw lines when the turtle moves
PenColour <colour> Tells the interpreter to draw the lines in
colour <colour>
Home Moves the turtle back to its home position and angle
SetHome Takes the current position and angle to be the turtles
home position and angle
Clear Clears the logo display window to the default white
ReStart Resets the entire logo display (not the program running)
Angle <degrees> Sets the turtle`s angle to <degrees>
Run Tells the interpreter to begin executing the currently
loaded logo textfile program
Most logo commands have minimum abbreviations, which can make
program entry easier.Many numeric parameters can have
mathematical expressions used in place of just numbers though
variables are not supported currently.Also note that the letter
case of the commands dosen`t matter, the interpreter will
recognise the command either way.
To find out a commands abbreviation use the help window
(available by clicking on help in the interpreters main menu
tree).Once the window is displayed click on the command you want
to know about.
Debugging your program
Debugging a logo program is mainly up to the user, however the
percentage display in the program status window, constantly
updated whilst a program is run, will indicate the percentage
through the programs textfile, the command where the error
occurred was after the bug is reached.
I have found a common sources of errors in programs are either
mistyped commands (generating `No such subroutine`) and missing
separators between statements (generating `Bad Logo parameter`).
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00000010 6f 67 6f 20 69 6e 74 65 72 70 72 65 74 65 72 20 |ogo interpreter |
00000020 42 79 20 44 75 6e 63 61 6e 20 46 2e 20 4d 63 50 |By Duncan F. McP|
00000030 68 65 72 73 6f 6e 0a 0a 20 20 20 20 20 20 20 20 |herson.. |
00000040 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
00000050 54 65 63 68 6e 69 63 61 6c 20 44 65 74 61 69 6c |Technical Detail|
00000060 73 0a 0a 57 65 6c 63 6f 6d 65 20 74 6f 20 6c 6f |s..Welcome to lo|
00000070 67 6f 20 56 32 2e 30 20 20 a9 20 41 72 63 68 69 |go V2.0 . Archi|
00000080 6d 65 64 65 73 20 57 6f 72 6c 64 20 31 39 39 33 |medes World 1993|
00000090 0a 0a 20 20 20 4d 79 20 6c 6f 67 6f 20 69 6e 74 |.. My logo int|
000000a0 65 72 70 72 65 74 65 72 20 69 73 20 6e 6f 77 20 |erpreter is now |
000000b0 66 69 6e 69 73 68 65 64 2c 20 61 6e 64 20 61 6d |finished, and am|
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000000d0 66 65 61 74 75 72 65 73 2c 20 69 74 20 6e 6f 77 |features, it now|
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000000f0 69 74 79 20 74 6f 20 73 61 76 65 20 79 6f 75 72 |ity to save your|
00000100 20 6c 6f 67 6f 20 70 72 6f 67 72 61 6d 60 73 20 | logo program`s |
00000110 0a 6f 75 74 70 75 74 20 61 73 20 61 20 73 70 72 |.output as a spr|
00000120 69 74 65 20 66 69 6c 65 20 6f 72 20 61 20 64 72 |ite file or a dr|
00000130 61 77 20 66 69 6c 65 20 28 73 6f 20 79 6f 75 20 |aw file (so you |
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00000150 65 6e 65 72 61 74 65 64 20 6c 69 6e 65 61 72 74 |enerated lineart|
00000160 20 69 6e 20 79 6f 75 72 20 44 54 50 20 64 6f 63 | in your DTP doc|
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00000180 68 65 20 69 6e 74 65 72 70 72 65 74 65 72 20 0a |he interpreter .|
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00000260 67 20 61 20 62 75 67 67 79 0a 0a 20 20 20 54 68 |g a buggy.. Th|
00000270 65 20 72 6f 62 6f 74 20 64 72 69 76 65 72 20 70 |e robot driver p|
00000280 72 6f 67 72 61 6d 20 61 6c 73 6f 20 63 6f 6d 65 |rogram also come|
00000290 73 20 77 69 74 68 20 61 20 66 75 6c 6c 79 20 77 |s with a fully w|
000002a0 6f 72 6b 69 6e 67 20 0a 64 72 69 76 65 72 20 70 |orking .driver p|
000002b0 72 6f 67 72 61 6d 2c 20 69 6e 20 69 74 73 20 61 |rogram, in its a|
000002c0 70 70 6c 69 63 61 74 69 6f 6e 20 64 69 72 65 63 |pplication direc|
000002d0 74 6f 72 79 20 28 75 6e 64 65 72 20 74 68 65 20 |tory (under the |
000002e0 66 69 6c 65 6e 61 6d 65 20 0a 32 4d 6f 74 6f 72 |filename .2Motor|
000002f0 73 29 2e 54 68 69 73 20 64 72 69 76 65 72 20 77 |s).This driver w|
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00000310 72 6e 20 55 73 65 72 20 70 6f 72 74 20 65 78 70 |rn User port exp|
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