24 09 12 1

Pagina 1

Principles of Programming Languages 2012.09.24 Notes • Total available time: 2h 30’. • You may use any written material you need. • You cannot use computers, phones or laptops during the exam 1 Haskell (10 points) 1. Please define a procedure getCSV that is used, in the Monad IO, to get a field in a Comma Separated Values textfile (assume as separators both the , and ; characters). 2. Define the unless procedure in the IO Monad. It takes two arguments, a condition c and a body b, and repeats b unless c becomes true (in a sense, it is a “dual” of while). 3. Alfio is experimenting with Haskell, and wants to define a very simple object-oriented-like system, where an object is just a container of a datum, and a list of “methods”, i.e. functions having signature a→ a→ a, where a is the type of the datum. This is an example object defined by Alfio: myob = Obj (5, [("add", \self -> \x -> self+x), ("sqr", \self -> \x -> self*self)]) -- x is ignored Please, help Alfio to define both the needed datatype, and the call function for invoking methods. E.g. call myob "add" -2 should return 3. 2 Prolog (8 points) 1. Please, define a Prolog procedure to obtain from a list the last but one element. If the number of elements in the list is less than 2, it should fail. 2. Define a nested version of the previous procedure: when the last but one element of the list is another list, this new procedure should look to the last but one element, until it finds an atomic value. E.g. ?- nestedlastb1([1,2,[3,3,[5,2,2],6],4],X). X = 2. 1 3 Scheme (7 points) Scheme does not natively support matrices: there are just vectors. Of course, we can define a matrix as a vector of vectors, each having the same size. 1. Please define make-matrix, with three parameters: r, c, and f ill. This procedure returns a matrix having…