> At the moment I have something working in many cases, but not all (attached)
> 
> It can do
> 	| y x |
> 	y := 10.
> 	x := 8.
> 	[:a :b | a + y + x] tempBindings 	" {'y'->10 . 'x'->8} "

... well in fact it can't, because just switching x and y in the block 
leads to:

	| y x |
	y := 10.
	x := 8.
	[:a :b | a + x + y] tempBindings	"  {'x'->10 . 'y'->8} "

So I'm stuck.

Stef