Learning is hard fun.—Marvin Minsky
Make the complicated comprehensible—Arthur Miller
Debugging is the learning opportunity of the 21st Century. — Cynthia Solomon
The important message that comes from ideas about debugging is that we learn from our mistakes; that the intricate process of making things work or learning new skills has to do with hypothesizing, testing, revising, etc.—Cynthia Solomon
Sometimes bugs are serendipitously adopted as features worth perpetuating, sometimes procedures must be constructed to deal with the phenomena caused by their appearance, and sometimes the bugs and their side effect need to be removed. But in this pursuit, children become creative researchers studying behavior, making up theories, trying out ideas, etc.—Cynthia Solomon
6 Stages of Debugging—Anonymous
- That can't happen.
- That doesn't happen on my machine.
- That shouldn't happen.
- Why does that happen?
- Oh, I see.
- How did that ever work?
Programming is hard. Art and Design is Fun. Both programming and drawing involve some trial and error and serendipity. Inevitably you will make mistakes along the way. Turtle Blocks provides a number of mechanism, reviewed below, to help you explore ideas and find mistakes.
The Play button (in top left corner) will run all of the Start blocks simultenously. (Every Turtle Blocks project has at least one Start block). But you can also run an individual stack of code by clicking on a stack. This lets you test and debug small sections of code, or, as in the example below, you can play a single voice by clicking on one of the Start blocks or single phase by clicking on one of the Action blocks.
Probably the most oft-used debugging aid in any language is the print statement. In Turtle Blocks, it is also quite useful. You can use it to examine the value of parameters and variables (boxes) and to monitor progress through a program.
The Print block (found on the Extras palette) can be used to print a message while running a program. It is useful to determine if a section of code is being executed when expected or if a box or parameter contains an expected value.
In this example, we use the addition operator to concatinate strings in a print statement. The mouse x + ", " + mouse y are printed in the inner loop. RUN LIVE
The Comment block (also found on the Extras palette) is similar to the Print block, except it only prints a message when the program is being run in Playback Slow mode (See below). Comments are also written to the browser console.
In this example, we use the comment block to get the value returned by the random block. RUN LIVE
The Status widget is a tool for inspecting the status of Turtle Blocks as it is running. By default the turtle co-ordinates and header are displayed. There is one row per turtle in the status table.
Additional Print blocks can be added to the Status widget to display additional turtle factors and graphics factors e.g.box values, x, y, heading, color, shade, grey, and pensize.
In this example, we use the status block to get the value of x,y,heading and colour . RUN LIVE
You can also do additional programming within the status block.
A "long press" on the Play button will invoke Playback Slow mode. The program will pause between the execution of each block and the block being executed will be highlighted. This is useful for following program flow, ensuring that the sequence of blocks being executed is what you expect. In addition, the value stored in any box or parameter is displayed on the block as the program runs, so you can "inspect" program elements as the program runs.
Run Step by Step advance one block per button press.
Clicking on the Play button will play your program at full speed. (It will also hide the blocks while the program runs, which improves performance.)
The above example show all the playback modes in order mentioned above.
First we started with Playback Slow moved on to Run Step by Step and finaly ended execution of remaining code with play
The Show and Hide blocks (found on the Extras palette) are useful for setting "breakpoints" in your program to debug a specific section of code. By putting a Show block at the start of a problematic section of code and a Hide block at the end of the section, your program can be run full speed until it gets to the Show block. Then the blocks are blocks are displayed and run in Playback Slow mode. When the Hide block is encountered, the blocks are hidden and the program resumes running at full speed.
As Turtle Blocks runs, some debugging information is written to the
browser console, such as the notes being played and comments (See the
Comment block above). The console can be accessed by typing
Ctrl-Shift-J on most web browsers.
Shown above is the console output from Example:10 turtle Experiment