Ch8, Ex2

I.Well, have a look at the kernel transform of the given program

local X in
   local Y in
      Y = X+1
      {Exchange C X Y}
   end
end 

Now its clear to see that X is unbound and above program will keep on waiting for X to bind(that'll never happen) at line Y=X+1 and will never execute Exchange. Here is the program with a simple fix:

L = {NewLock}
lock L then X Y in
   {Exchange C X Y}
   Y = X+1
end 

II. The simple fix that I have given above will not work in a language that doesn't have dataflow variables because it is *using* dataflow behavior of variable Y to work.

III. Another fix that doesn't use dataflow variables and hence, is possible in a language without dataflow variables:

L = {NewLock}
lock L then
   C:=@C+1
end