Scratch

johncpw wrote:

I have try to simulate 'function' by using boardcast, but can I simulate recurrion? I remeber I can define function and recurrion in traditional LOGO.

I think you are talking about "recursion".  Take a look at Jens work

http://scratch.mit.edu/users/jens

he has done a lot of work with recursion.  He has even made his own version of Scratch that supports recursion directly.

You can simulate recursion using a List as a stack...here is an example

http://scratch.mit.edu/projects/Paddle2SeeFixIt/482887

The tree is drawn by repeatedly calling the Draw One Branch routine.

Hi coolstuff.

wikipedia wrote:

Recursion
        If you still don't get it, see: "Recursion".

Recursion usually refers to a function calling itself, i.e. in order to navigate a tree-node or determine a number's factorial.

Logo is a wonderful programming language, and in many ways Scratch's predecessor.

Jens wrote:

Hi coolstuff.

wikipedia wrote:

Recursion
        If you still don't get it, see: "Recursion".

Recursion usually refers to a function calling itself, i.e. in order to navigate a tree-node or determine a number's factorial.

Logo is a wonderful programming language, and in many ways Scratch's predecessor.

Paddle2See wrote:

Well, the definition is here

http://en.wikipedia.org/wiki/Recursive_definition

but it's pretty hard to understand.  Maybe an example would help:  factorials of numbers.  To get the factorial of a number you multiply that number by all the positive integers less than that number.  So the factorial of 6  = 6*5*4*3*2*1 = 720.  The symbol for factorial is the exclamation mark so another way to say the same thing is

6! = 6*5*4*3*2*1 = 720

But if we look at that more closely, we can see that it is the same as 6 times the factorial of 5.  So we can write

6! = 6 * 5!

Or, for any positive integer number N

if N = 1 then N! = 1
If N > 1 then N! = N * (N-1)!


So this is a recursive definition of the factorial operation...since it includes itself in the definition.  Kind of weird, huh?  But you could use this definition (and many people do) to write a recursive program that calculates factorial numbers.

Thanks!

*stares at what Paddle2See wrote* uhhhhhhhhhhhh... I think I get it. *n*