Computer Science 3675
Summer 2000
Quiz 4

1. Write a clearly legible T to the left of each of the following that is true, and a clearly legible F to the left of each that is false.
   1. A genuinely strongly typed language such as Standard ML does not need to perform any type checking at run time.
   2. Most object-oriented programming languages are strongly typed.
   3. All programming languages employ types at compile time.
   4. Polymorphism is most useful in creating general purpose libraries.
   5. Object-based programming is centered around the notion of a class.
   6. Under the name equivalance rule, two types with different names must be different types.
   7. An implementation of a typeless language does not do any type checking at all, at compile time or run time.
2. What is the most general polymorphic type of function f defined by f(x) = tail(left(x))? Function tail takes the tail of a list, and left takes the left-hand member of an ordered pair. Use and as type variables. Answer:
3. Function filter is defined so that (filter p x) returns the list of all members of list x that cause predicate p to return true. For example, suppose that function pos is defined so that pos(n) is true just when n is positive. Then (filter pos [9,-3,8,-2]) = [9,8]. Notice that (filter pos) is a function. What is the most general polymorphic type of filter? Use and as type variables. Answer:
4. Explain how variable selectors are inherited in single-inheritance object-oriented programming languages.

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