What purpose is served by universal reference types? What is type inference? Describe three contexts in which it occurs. Under what circumstances does an ML compiler announce a type clash? Explain how...

What purpose is served by universal reference types? What is type inference? Describe three contexts in which it occurs. Under what circumstances does an ML compiler announce a type clash? Explain how the type inference of ML leads naturally to polymorphism. Why do ML programmers often declare the types of variables, even when they don’t have to? What is unification? What is its role in ML?