Modifying the Program for Strategies: Exercise 6.13, pp. 156-7

• Exercise 6.13 walks you through the process of creating a move instruction ADT that is analogous to the game state ADT.

• A move instruction basically bundles into one data type a number of coins and a pile to take them from. So that your program works consistently with the Nim server (discussed later), use the following move instruction ADT representation:

     (define make-move-instruction cons)
  
     (define coins car)
  
     (define pile cdr)
  

  After adding these definitions to nim.scm, the ADT can be used as shown below. A move instruction to take 7 coins from pile 2 is created and then accessed.

     > (define move (make-move-instruction 2 7))
     > move
     '(2 . 7)
     > (pile move)
     7
     > (coins move)
     2
     > 
    

• The exercise then has you modify your program to use move instructions but to behave the same as it did before. Note that remove-coins-from-pile will be replaced by a new procedure next-game-state.