There are many restrictions compared to LOGO. The two allowed user-defined procedures can't have parameters. Only two numeric global variables are available, no lists or other data-structures. You can't make user defined functions which return a value. The conditionals and some of the functions only take constants or variables, not expressions. Limited screen real-estate makes building large programs unfeasible.
There are five palettes of program elements available for program construction. You add blocks to your program by dragging them from the palette to the main area. You can delete a block by dragging it back onto the palette. Click anywhere on an existing "stack" of blocks to start executing that stack.
- Clean - clear the screen and reset the turtle to center, pointed up (pen down, bright red)
- Turtle state values (can plug into a parameter)
- X, Y, heading (Zeros for each are center screen, pointed up. Heading is degrees clockwise.)
- Pen Up
- Pen Down
- Set Pen Size(n)
- Set Color(n)
- Set Shade(n)
- Fill Screen(color,shade)
- Pen state values (can plug into a parameter)
- Pen size, color, shade
- Any idea of the allowed ranges of these variables? (Color/shade appears to be Hue/Brightness.)
- Values (can plug into a parameter)
- Number (constant)
- Infix operators(left,right)
- +, -, *, /, mod
- Random(min, max) (constants or boxes only)
- Conditions (oval, plugs into an If block)
- <, >, = (takes two constants or boxes)
- and, or, not (takes other conditions)
- Print(n) - Debugging output. When in full screen mode (Alt-Enter), show a numeric value at the bottom of the screen.
- Forever[stack] (no continuation)
- Stop (no continuation)
- jog right
- jog down
My blocks (yellow)
- Stack1,2 - a rhombus which tops a stack, equivalent to a procedure definition (but without parameters).
- "Stack1,2" - blocks for invoking a stack (no parameters)
- Store in "box" 1,2(n) - blocks for setting a variable
- "Box1,2" (plugs into a parameter)
- A glaring limitation: you cannot rename these objects. Thus, you are limited to two procedures and two global variables! Madness! --IanOsgood 13:59, 30 December 2007 (EST)
Program control icons
There are also some icons at the bottom right for user control:
- Show/Hide the current program
- Eraser - clear the screen and reset the turtle (same as the Clean block)
- Stop (for infinite loops)
The Project tab at the top left gives access to sample programs shipped with the activity.
<gallery> Image:Turtle0.png|Turtle Art startup screen Image:Turtle1.png|Clicking on the Blocks menu brings the basic tool set into view Image:Turtle2.png|Drag blocks from the menu Image:Turtle3.png|Click on the top block of a stack to execute the stack Image:Turtle4.png|Other blocks can be found under the tabs Image:Turtle5.png| Image:Turtle6.png|Example projects are found on the Projects menu on the upper right of the screen Image:542-turtleart-2.png Image:Turtle-recursion-1.jpg|A recursive algorithm (difficult without parameters)