Parallel Scratch

Note: this is still just a draft…

In some of your Scratch projects so far, you might have seen some scripts that look like this:

forever
  if <key [up arrow v] pressed> then
    change y by (10)
  end
  if <key [down arrow v] pressed> then
    change y by (-10)
  end
  if <key [left arrow v] pressed> then
    change x by (-10)
  end
  if <key [right arrow v] pressed> then
    change x by (10)
  end
end

This code follows a single line of steps one after the other. This approach has only one step running at once. Scratch can only ever be reacting to one key at a time.

What would it look like if we split that up so that Scratch did more of the work behind the scenes, and our code did less work?

For example:

when [up arrow v] key pressed
change y by (10)

when [down arrow v] key pressed
change y by (-10)

when [left arrow v] key pressed
change x by (-10)

when [right arrow v] key pressed
change x by (10)

Now we have five less blocks, the code is smaller and hopefully faster. Not only that, Scratch can now react to multiple keys at a time internally. We now have multiple code blocks running in ‘parallel’.

We can make our projects more flexible by reacting to different Scratch events like this rather than creating one big loop with lots and lots of if checks in them.