GIML: Tutorial Six: Hints

The sum function might be defined for lists of reals as follows:

fun sum nil = 0.0
|   sum (h::t) = h + sum t;

However we can use reduce instead:

val sum = reduce (op +) 0.0;

Either way we need to map the appropriate function over the list of countries to obtain a list of populations or GDP's first.

map pop europe;

gives a list of populations which can be summed.

sum (map pop europe);

The major countries might be definied using the function major which takes a country and returns true if it's population is at least 1 million.

fun major country = (pop country > 1000000.0);

We can then obtain a list of major countries by filtering the main list.

filter major europe;