Scratch

I don’t expect my kids to become programmers like their dad. I wouldn’t wish it for them unless it is what they want for themselves. Still, I think there is value in getting exposure to programming for a number of reasons – thinking logically, planning, designing, applying math, understanding how things work and fostering creativity to name a few.

The question is when and how to introduce kids to programming. Scratch may be the answer to how and right about now the answer to when. Scratch is a new language from the Lifelong Kindergarten group at the MIT Media Lab designed to make it fun and easy for kids 8 and up to create programs. My kids and I found Scratch instantly compelling. Everything about Scratch, from the friendly looking cartoon cat that starts out in each new project, to the building block style programming, to the sharing of projects on the Scratch web site has been designed for and appeals to the youngest possible audience.

My kids are at the young end of the target age range for Scratch so I don’t expect too much programming from them at this point. The important thing is that they are really excited to use the program. They create projects to collect, edit and arrange pictures. They are interested in seeing and trying the projects that other people have created. It provides a context for me to talk to them about things like the X, Y coordinate system in terms of the number line they already know and what it is used for in moving things around on the screen.

Just the other night I was sitting with my youngest and she had chosen a cartoon girl sprite and a bedroom background. Then she asked “can we make her jump up and down on the bed”. I said “sure” and in a few minutes I showed her how. A block to move up. Click, a block to move down. Put them in a repeat loop, click. How many times do you want her to Jump? Twenty, OK. Oops, too fast. Click, add a wait block. Done. Then I introduced her to variables so she could control how many times the girl jumped.

The Scratch web site provides a social network where people (I say people because it is not just kids playing with Scratch) can share their projects and ideas. Any uploaded project can be downloaded by anyone so they can open it up and learn how it works or simply just play with it. This really fosters learning and building on the ideas of others. You will see some comments complain of copying or ripping off ideas but overall the site promotes an attitude of sharing. Knowledge and ideas are not a scarce resource to be horded and protected they are abundant and should be shared. Many people share projects that demonstrate a particular technique and encourage others to use it in their own projects.

I am very impressed with the projects on the Scratch web site. There are over 32,000 projects as of this writing, which is impressive since the program only came out in May of 2007. Some projects are artistic perhaps using color cycling or other graphic effects to make their pictures come to life. Some are animated stories. Some are musical. Some interactive. There are plenty of video game style projects ranging from imitations of classics like Pac-Man or Donkey Kong to original ideas. There are projects exploring science and math and many show a great deal of sophistication.

The usability of the development environment is superb. It is well organized and intuitive. It is also visually attractive. What I find most impressive, for such a new product, is that it is rock solid. I used it a number of hours over the course of a week often leaving it running for days without a single crash, glitch or loss of data.

Programming is done by putting together statement blocks such as and control blocks such as . As far as I can tell it is not possible to get an error message no matter how you put the blocks together. It may not do what you want but it will not complain that you did something wrong. Feedback is immediate. Just double click a block to see what it will do. Another great feature is that you can change your program while it is running.

Scratch is implemented in squeak. When the projects are uploaded to the web site they run as a Java applet. I have noticed some differences between the behavior of my project when run in Scratch and as an applet but the differences are minor. Probably just display glitches in the Java graphics routines.

How about the Scratch language itself? Well from an experienced programmer’s point of view the language is extremely limited. For example, variables can only hold numbers, there are no string manipulation operations, and there are no arrays or collection data types. Not surprisingly the programs are event driven. Groups of statement or control blocks are run when the start flag is pressed, a key is pressed, when a sprite is clicked or when a message is received. Messages are broadcast and all handlers act on the message. You can define as many messages as you like. Messages cannot have arguments which is one of the most limiting things. The message handlers are the closest thing to a subroutine but because there is no argument passing all information flows through global variables. I would say that it is a strongly typed language in the sense that the round edges of a numeric value will not fit where the sharp edges of a Boolean expression are expected. Variables must be declared.

Simple things like prompting for a name and then outputting "Hello " + name is very difficult due to lack of input/output and string manipulation primitives. However things that would be complex in other environments like hit tests between two moving sprites are trivial. I had to remind myself that I am not their target audience and everything left out was probably left out for a good reason – usability.

I am not a big fan of graphical programming languages. I quickly got tired of the Lego Mindstorms block programming language and switched to NQC. I found the Mindstorms programming environment to be slow, noisy, and inefficient. All of the graphical programming languages I have ever tried I found to be far inferior to text. Scratch is no exception but it is the best interface I have see yet. I also think it is just the right thing for young kids. Having visual blocks to move around really maps well to the physical world they are used to manipulating.

I do hope the language gets extended. I would like to see advanced users be able to explore programming concepts such as recursion.

Like I said, its not just my kids that find Scratch compelling. I wanted to play with it as well. I rationalized that by learning it I would be better able to help explain it to my kids but I like creating things no matter what the medium.

My first project is Addition Tutor. It is an interactive program to learn and practice addition of up to 3 digit numbers. I decided on this project because of the challenge of inputing and displaying numbers in Scratch and because it is something that I’m teaching my kids now.

Scratch is not the first programming language with kids in mind. Way back when there was Logo and more recently KPL. I took a quick look at KPL and it looks like visual basic to me. Unlike Scratch there was nothing enticing me to try it out. The first thing you may ask about a language is what can I do with it. What better way to answer that question than with a web site with thousands of examples all of which you can download and try.