Debugging
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 effects 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. Composing music is also hard. Both programming and composing involve some trial and error and serendipity. Inevitably you will make mistakes along the way. Music Blocks provides a number of mechanisms, reviewed below, to help you explore ideas and find mistakes.
The Play button (in top left corner) will run all of the Start blocks simultaneously. (Every Music 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.
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.
The Print block is used to display the number of whole notes played, in this case, 1/4 + 1/4 + 1/2, which adds up to 1, which is displayed at the top of the browser window.
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.
The Status widget is a tool for inspecting the status of Music Blocks as it is running. By default, the key, BPM, and volume are displayed. Also, each note is displayed as it is played. There is one row per voice in the status table.
Additional Print blocks can be added to the Status widget to display additional music factors, e.g., duplicate, transposition, skip, staccato, slur, and graphics factors, e.g., x, y, heading, color, shade, grey, and pensize.
You can do additional programming within the status block. In the example above, whole notes played is divided by 4 (e.g. quarter notes) before being displayed.
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.) But there are two other playback modes.
On the Secondary Menu, there are two other Play buttons.
During 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 advances one block per button press.
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 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 Music 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 three notes: sol mi sol.