5 Higher order Functions on Lists

  1. try:
    use list;
    double:num -> num;
    double(n) <= n*n;
    map double [1,2,3,4];
    map (lambda x => x*x) [1,2,3,4];
  2. try

    use list;
    type string == list(char);
    type student == string X string;
    type class == list(student X num);
    c <= [(("Fred","Jones"),66),(("Ali","Mohamed"),76),(("Mary","Ward"),92),(("Colin","Gold"),31)];
    map (lambda ((x,y),z) => x) c;
    map (lambda ((x,y),z) => z) c;
    foldr  (0 ,(+))  (map (lambda ((x,y),z) => z) c);
    (foldr  (0 ,(+))  (map (lambda ((x,y),z) => z) c))/length(c);
    averageClass: class -> num;
    averageClass k <= (foldr  (0 ,(+))  (map (lambda ((x,y),z) => z) k))/length(k);
    averageClass	 c;
    type course == string X class;
    c1: course;
    c1 <=("CS1", c);
    c2: course;
    c2 <=("Maths", [(("Fred","Jones"),36),(("Ali","Mohamed"),56),(("Mary","Ward"),45),(("Colin","Gold"),71)]);
    averageCourse:course -> num;
    averageCourse(x,y) <= averageClass(y);
    averageCourse c1;
    type degreeprogramme == list(course);
    cs <= [c1,c2];
    map averageCourse cs;
    map (lambda (x,y) => (x, averageCourse (x,y))) cs;

  3. Redo all last week's exercises using higher order functions.

  4. Look at the files on igor in directory: /usr/local/share/hope/lib. That explains the point of use list; at the beginning of the above.

Sebastian Danicic BSc MSc PhD (Reader in Computer Science)
Dept of Computing, Goldsmiths, University of London, London SE14 6NW
Last updated 2011-03-15