CMSC330 - SUMMER 2006 - PSEUDO-MIDTERM 2
INSTRUCTOR: GUILHERME FONSECA
•Write all answers in the answers book provided.
•You can keep the exam. Only return the answers book.
•You are allowed to consult one letter-size paper, handwritten on one side. Besides that, the
exam is closed book, closed notes.
•There are 9 questions, totaling 100 points, in this exam. You have 1 hour and 20 minutes
to finish it.
(1) (15 points) Give short anwers:
(a) Garbage collection makes dangling pointers impossible. Give one short fragment of C
language code which tries to access the memory pointed by a dangling pointer.
(b) There are two basic techniques that can be used to simulate multiple arguments in
OCaml: tuples and Currying. Give one advantage of Currying compared to using
tuples to simulate multiple arguments.
(c) Describe a language that is context-free, but not regular.
(2) (10 points) The fold function can be written in OCaml as:
let rec fold f a l =
match l with
[] -> a
| (h::t) -> fold f (f a h) t
Write a fold function with a similar behavior in Ruby using codeblocks. The following
Ruby code should work with your fold function and return the sum of the elements in an
Array:
fold([5, 5, 3, 1],0) {|x,y| x+y} # Returns 14
(3) (15 points) What is the type of fin each of the OCaml lines below.
(a) let f = (2*3, 2.0 *. 3.0)
(b) letfx=1
(c) letfxy=x+.y
(d) let f (x,y) = x::y
(e) let f x y z = (x y)::z
(4) (10 points) Write a merge function in OCaml that receives two sorted lists and returns the
sorted list containing the elements that are in either list, as the example below. You can
assume that no element will appear multiple times in the input lists. Do not use any library
function. All listed are sorted in increasing order, accoding to OCaml comparison operators
(<,>,<=...).
merge [1; 2; 7; 9] [3; 5; 8; 12]
(* Returns [1; 2; 3; 5; 7; 8; 9; 12] *)
The type of your function should be:
’a list -> ’a list -> ’a list
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