Drill 5

1. Does the current compiler ever put the address of a memory location on the heap onto the stack?

2. Does the current compiler ever put the address of a memory location on the heap into a register?

3. How many 8-byte heap "cells" will be used when each of the following programs are compiled and executed? (Remember that each pair takes up two cells).

   • (+ (left (pair 1 2)) (right (pair 3 4)))
     

   * 4

   • (let ((x false)) 
         (pair 1 (if x (pair 2 (pair 3 (pair 4 false))) 
                         (pair 2 (pair 3 false))
                 )
         )
     )
     

   * 6. Remember that only one branch of the conditional will actually be executed: in this case, the `else` branch! We can't count heap usage just by counting occurences of `pair`.

4. For each expression below, will it result in an error or a valid result when run in the interpreter we have built in class?

   program	error	valid result
   (+ 1 3 4)
   (+ 1 (let ((x 2)) x))
   (+ 1 (let ((x 2)) false))
   (left (pair 1 false))
   (left (left (pair 1 false)))
   (** 2 3)
   (if true (* 2 3) (** 2 3))

5. For each expression below, will it result in a compile-time error, a run-time error, or a valid result when run in the compiler we have built in class? (Assume that we have added error handling for all supported operations).

   program	compile error	runtime error	valid result
   (+ 1 3 4)
   (+ 1 (let ((x 2)) x))
   (+ 1 (let ((x 2)) false))
   (left (pair 1 false))
   (left (left (pair 1 false)))
   (** 2 3)
   (if true (* 2 3) (** 2 3))

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