Csci 4651 Problem set 6

Due Wednesday, October 29 in class

Problem 1 (18 points): type inference.

Apply the type inference algorithm to the examples below. Show all your work. Write down the resulting type for the function f in each case (or demonstrate a type mismatch if the function does not have a valid type). Feel free to use the OCaml interpreter to check your types.


(* Question 1 *)
let f x y = if x < 2 then x :: [] else x :: [y];;

(* Question 2 *)
let f x = fst x :: snd x ;;

(* Question 3 *)
let f x = match x with
  (y, []) -> y
 |(z, w) -> z + w;;

(* Question 4 *)
let rec f x = match x with 
  [] -> []
 |y :: ys -> (not (y < 2)) :: f ys;; 

Problem 2 (4 points).

Exercise 6.3 p. 157. "No conversion" means that the contents of the memory location (the sequence of 0s and 1s) is left unchanged.

Problem 3 (8 points).

In the following Java program please point out all L-values (expressions that are used to denote a memory location) and R-values (expressions used to denote a value in memory).

import java.awt.*;

public class LRValues {

    public static void main(String [] args) {
        int x = 0;
        x++;
        boolean y = (x == 0);
        if (y) {
            y = !y;
        }
        int [] A = {1, 2, 3};
        for (int i = 0; i < 2; ++i) {
            A[i] = A[i+1];
        }
        Point thePoint = new Point();
        thePoint.x = thePoint.x + 1;
    }

}

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