On Sun, Feb 05, 2006 at 01:29:06PM +1100, skaller wrote:
> On Sat, 2006-02-04 at 22:19 +0100, Oliver Bandel wrote:
> > Hello,
> > 
> > 
> > how to implement a simple non-trivial machine (Heinz von Foerster)
> > in a purely functional manner?
> 
> Define a record S containing your state variables.

Is it necessary to have state-variables in a record?
Is it then (with records) functional implementation?!

> 
> Write a pure function f: S -> S representing one tick of the  
> system clock.

Hmhhh.... ok, I see.

But I'm not clear about how to write this function "f",
because it needs mutual recursion...
In a purely impeative way I think i woulf find a solution,
but thinking about it in Ocaml => blackout. ;-(


> 
> Then write
> 
> 	let rec run f S = 
> 		let S' = f S in
> 		if S' = S then S
> 		else run f S'
> 	in 
> 	run f S0
> 
> Note it may never terminate, it isn't hard to build
> an oscillator :)

Well, the run-function is not what I was looking for, because
the loop is intended to work again and again, so, it is not
necessary to have the if-then stuff inside: each clock
cycle reads in a new input-value and calculates a new output value
and then calls itself again...

and inside "f" there also is a feedback.

See the second picture in the jpeg-file:

    http://www.belug.org/~ob/struktur-grafisch.jpg



Ciao,
   Oliver