Newtro Logo

Logo is the programming language that put a turtle on the screen in 1967. Type a command at the ? prompt and the turtle carries it out. Teach it new words with TO, and it remembers them next time you visit.

? FD 100

This terminal needs JavaScript to run.

Turtle speed 0 draws instantly

Try a program

Each one runs in the terminal above. Read the code, run it, then change a number and see what happens.

A square

Four steps forward, four quarter turns.
```
CS
REPEAT 4 [FD 120 RT 90]
```
A star

Turn 144 degrees five times and the lines cross into a star.
```
CS SETPC 6
REPEAT 5 [FD 200 RT 144]
```
Spinning squares

A loop inside a loop, with a new color on every turn.
```
CS SETPENSIZE 2
REPEAT 12 [
  SETPC REPCOUNT
  REPEAT 4 [FD 110 RT 90]
  RT 30
]
```

A square spiral

A procedure that calls itself, growing a little each time.

TO SPIRAL :SIZE
  IF :SIZE > 240 [STOP]
  FD :SIZE RT 91
  SPIRAL :SIZE + 3
END
CS SETPC 3 SPIRAL 2

A tree

Every branch is a smaller tree. This is recursion.

TO TREE :SIZE
  IF :SIZE < 6 [STOP]
  FD :SIZE
  LT 25 TREE :SIZE * 0.7
  RT 50 TREE :SIZE * 0.7
  LT 25 BK :SIZE
END
CS SETPC 2
PU BK 190 PD
TREE 110

A snowflake

The Koch curve: each line becomes four smaller lines.

TO SIDE :SIZE :DEPTH
  IF :DEPTH = 0 [FD :SIZE STOP]
  SIDE :SIZE / 3 :DEPTH - 1
  LT 60 SIDE :SIZE / 3 :DEPTH - 1
  RT 120 SIDE :SIZE / 3 :DEPTH - 1
  LT 60 SIDE :SIZE / 3 :DEPTH - 1
END
CS SETPC 11
PU SETXY -150 90 PD SETH 90
REPEAT 3 [SIDE 300 3 RT 120]

Flower of circles

ARC and CIRCLE draw curves around the turtle.

CS HT
FOR [I 1 18] [
  SETPC 1 + MODULO :I 6
  PU FD 60 PD CIRCLE 60
  PU BK 60 RT 20
]
PD ST

Our wordmark

NEWTRO is a procedure too. Type PO "NEWTRO to read it.
```
CS NEWTRO
```

Everything the turtle understands

Short forms are in brackets. Commands work in upper or lower case. The turtle starts in the middle facing up, and 0 degrees is straight up.

Moving

FORWARD 100 (FD): Move forward 100 steps.
BACK 50 (BK): Move backward.
RIGHT 90 (RT): Turn clockwise by degrees.
LEFT 45 (LT): Turn counterclockwise.
HOME: Return to the middle, facing up.
SETXY 50 -20: Go straight to a point.
SETHEADING 180 (SETH): Face a direction.
ARC 180 50: Draw part of a circle around the turtle.
CIRCLE 40: Draw a full circle around the turtle.

Pen and screen

PENUP (PU): Move without drawing.
PENDOWN (PD): Draw again.
PENERASE (PE): Rub out lines as you move.
SETPENCOLOR 4 (SETPC): A color number, a name like "RED, or [R G B] from 0 to 255.
SETPENSIZE 3: Make the line thicker.
SETBACKGROUND 1 (SETBG): Change the screen color.
CLEARSCREEN (CS): Wipe the screen and go home.
HIDETURTLE (HT): Hide the turtle. SHOWTURTLE (ST) brings it back.
LABEL "HELLO: Write text where the turtle is.
SPEED 10: From 1, slow, to 10, fast. 0 is instant.

Repeating and deciding

REPEAT 4 [ ... ]: Run the list a number of times. REPCOUNT says which time it is.
FOR [I 1 10 2] [ ... ]: Count from 1 to 10 in steps of 2.
IF :X > 5 [ ... ]: Run the list only when the test is true.
IFELSE test [ ... ] [ ... ]: Choose between two lists.
WHILE [test] [ ... ]: Keep going while the test is true.
FOREVER [ ... ]: Keep going until you press Esc.
WAIT 60: Pause. 60 is one second.

Teaching new words

TO SQUARE :SIZE ... END: Define a procedure with inputs. Type it over several lines.
STOP: Leave the procedure now.
OUTPUT value (OP): Give a value back to whoever asked.
MAKE "SIDE 50: Store a value. Read it back with :SIDE.
LOCAL "X: Keep a variable inside one procedure.
POTS: List your procedures. PO "NAME shows one.
ERASE "NAME (ER): Forget a procedure. ERALL forgets them all.

Numbers and words

+ - * / = < >: Arithmetic and comparisons.
PRINT SUM 2 3 (PR): Show a result. SHOW keeps list brackets.
RANDOM 10: A whole number from 0 to 9.
SQRT, POWER, SIN, COS: Math, with angles in degrees.
INT, ROUND, ABS, MODULO: Tidy up numbers.
FIRST, LAST, BUTFIRST, ITEM: Take apart words and lists.
LIST, SENTENCE, WORD, PICK: Build them up, or choose at random.

The terminal

HELP: A quick reminder.
Up and down arrows: Bring back earlier commands.
Esc: Stop a running program.
Paste: Paste a whole program to run it at once.
CLEARTEXT (CT): Clear the text lines.
GAMES: What else we're making.

Pen colors

0 black
1 blue
2 green
3 cyan
4 red
5 magenta
6 yellow
7 white
8 brown
9 tan
10 forest
11 aqua
12 salmon
13 purple
14 amber
15 gray

Why a turtle?

Wally Feurzeig, Seymour Papert and Cynthia Solomon created Logo in 1967 so children could learn by making things. The turtle started as a small robot that crawled across the floor with a pen. It moved onto screens, and into school computer labs everywhere.

Our puzzle game One Command Ahead grew from that same idea: a few clear instructions, a very literal machine, and the fun of watching your plan play out.

Visit onecommandahead.com Read the history of Logo