5 return f(l.hd) : map(f, l.tl);
13 return foldr(f, f(acc, l.hd), l.tl);
22 return filter(f, l.tl);
24 return l.hd : filter(f, l.tl);
33 return x : intList(x-1);
47 // print("faculty of 5 is: ", foldr(\x y->x*y, 1, intList(5)));
48 // print("sum of 1..5 is: ", foldr(\x y->x+y, 0, intList(5)));
49 // print("sum of 0..12 but only the evens: ",
50 // foldr(\x y->x+y, 0, filter(\x->x%2 == 0, intList(12))));