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Turtle Roy == Roy with Turtle Graphics
JavaScript C++ Perl C HTML Inno Setup Other

Turtle Roy

A Roy programming/learning environment with Turtle Graphics, as in the Logo programming language.

Try it online:

Turtle Roy API

Command Result
fd 100 moves 100 pixels forward
lt 45 turns left 45 degrees
rt 90 turns right 90 degrees
penup lifts the pen, no trace left when moving
pendown lowers the pen again for drawing
setshape "rocket-large" changes the cursor. available (with and without -large): butterfly, car, fairy, formula, princess, rocket, turtle
clear clear the paper and reset turtle to center
home reset the turtle to center
say "wat" speak!
print "x" print to console
login "raimo" login as "raimo" (this is the author name in your saved work)
save "asdf" save current work as "asdf"
open "asdf" open saved work "asdf" (presuming you've saved with this name and current author name)
whoami show the author name of the logged-in user (this is just saved in a cookie)
ls list your saved works
play c plays the note C
play c 500 plays the note C for 500 milliseconds
play c*2 plays the note C2 (frequency = C * 2)
sequence [fd 100, rt 90] 100 pixels forward, then right turn
s [fd 100, rt 90] same as above
repeat 4 (say "hello") says "hello" 5 times
r 4 (say "hello") same as above
par [play c, play e] playes notes C and E in parallel
bg "red" change background color (red, rgb(255,0,0), #FF0000)
color "red" change pen color (red, rgb(255,0,0), #FF0000)
text "HELLO" draw the text "HELLO" beside the turtle
font "40px Arial" changes to the 40px Arial font
font 100 changes to the 100px Courier font

Array / List API

Example Result Description
range 1 3 [1,2,3] range of numbers
length [1,2,3] 3 list length
empty [1] false is list empty
concat [1,2] [3] [1,2,3] concatenate lists
cons 1 [2,3] [1,2,3] prepend to list
head [1,2] 1 first item on list
tail [1,2,3] [2,3] all but first item on list
last [1,2] 2 last item on list
times 2 "yes" ["yes", "yes"] repeat same element
sum [1,2,3] 6 sum of items on list
map (\x -> x * 2) [1,2] [2,4] map list items with function
filter (\x -> x ==1) [1,2] [1] filter list with function
zip plus [1,2] [3,4] [4,6] zip lists pairwise with function
scanl plus 0 [1,2,3] [0,1,3,6] accumulate values, output all
foldl plus 0 [1,2,3] 6 accumulate values, output last

In addition to this, you may use the full Roy programming language.


Bunch of examples available in the demo menu. Some more stuff here.

Basic Turtle commands

fd 100
lt 90
rt 45


let square = repeat 4 (sequence[fd 50, lt 90])


let flower = repeat 36 (sequence[rt 10, square])


3 + 4
3 / 4
let factorial n = if n==1 then 1 else n * (factorial n - 1)
factorial 12


"apple" ++ "sauce"
"apple" + 10 (won't compile)


range 1 99
times 100 "lol"
head [1,2,3]
tail [1,2,3]
concat [1,2,3] [4,5,6]
length [1,2,3]
empty []
let reverse xs = if (empty xs) then [] else concat (reverse (tail xs)) [head xs]
reverse [1,2,3]
sum [1,2,3]
map (\x -> x * 2) [1,2,3]
filter (\x -> x > 1) [1,2,3]
foldl (\x y -> x * y) 1 [1,2,3]

Building and running

Build (and rebuild on javascript changes)

npm install

Run the server (node.js / express)



open http://localhost:8070

Optionally also start the mongo db



Thanks to Miikka "arcatan" Koskinen for creating tryroy, from where I shamelessly stole the Roy browser REPL.

Thanks to Brian McKenna for the Roy language and support.

See origins of the cursor images from src/main/webapp/images/image-sources.txt

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