README.md

Blood donations

There are four blood groups, A, B, AB and O:

type blood_group = A | B | AB | O

A blood donation is possible only if the blood group of the donor is compatible with the blood group of the recipient.

The compatibility relation is illustrated in the directed graph below, where an edge from x to y indicates that a patient with blood group x can give blood to a patient with blood group y.

Define a function check_groups that takes the blood groups of two different patients and checks if the first patient can donate blood to the second patient. The type must be:

check_groups : blood_group -> blood_group -> bool

For example, the following asserts must pass:

assert (check_groups O AB = true);;
assert (check_groups A B = false);;
assert (check_groups AB AB = true);;