Happy new year!

Here is a new year's resolution: by July 2015, we will freeze the Pencil Code interface so that we can build curriculum without worrying about removed features. So mail me any ideas of things that need to be changed in Pencil Code before then - info@pencilcode.net.


The first change for 2015 is forever.

forever lets you repeat something indefinitely. Put an arrow -> after it, then indent code that you want to repeat.

forever ->  
  fd 2
  rt 2

It is useful for making animations. The previous version of this function was called tick. The difference is that forever lets you set up more than one loop to run at once:

forever ->
  fd 2
  rt 2

forever ->
  pen random color

The two processes run in parallel forever, so the pen continually changes color as the turtle moves.

stop() nothing is forever

Inside a forever loop, stop() will stop the repetitions. The following program will run the forever loop, watching for the w and down s keys on the keyboard. One of them will increase v and make the turtle move. The other will stop the forever loop.

v = 0
forever ->
  fd v
  if pressed 'w'
    v = v + 0.1
  if pressed 's'

forever loops are different from for and while loops. forever is a function whose loops are stopped by calling the function stop().

for and while are loops that are built-in to the language. To stop those loops, use the built-in command break.

The speed of forever

The forever function can be set to repeat at any number of repetitions per second. Just add an optional number before the arrow:

forever 1, ->
  dot random color
  rt 30
  fd 25

The number is the number of repetitions per second.