Chap 15 - Review Question and Problem Set - Concepts of Programming Languages, Sebesta

CONCEPTS OF

PROGRAMMING LANGUAGES

TENTH EDITION

Robert W. Sebesta

Chapter 15-Functional Programming Languages

Review Question

5. Explain why QUOTE is needed for a parameter that is a data list.
Answer: To avoid evaluating a parameter, it is first given as a parameter to the primitive function QUOTE, which simply returns it without change.

6. What is a simple list?
Answer: A list which membership of a given atom in a given list that does not include sublists.

7. What does the abbreviation REPL stand for?
Answer: REPL stand for read-evaluate-print loop

8. What are the three parameters to IF?
Answer:
The Scheme two-way selector function, named IF, has three parameters: a predicate expression, a then expression, and an else expression. A call to IF has the form (IF predicate then_expression else_expression)

11. What are the two forms of DEFINE?
Answer:
DEFINE takes two lists as parameters. The first parameter is the prototype of a function call, with the function name followed by the formal parameters, together in a list. The second list contains an expression to which the name is to be bound.

18. What is tail recursion? Why is it important to define functions that use recursion to specify repetition to be tail recursive?
Answer:
A function is tail recursive if its recursive call is the last operation in the function. This means that the return value of the recursive call is the return value of the nonrecursive call to the function. It is important to specify repetition to be tail recursive because it is more efficient(increase the efficiency).

27. What is the use of the fn reserved word in ML?
Answer: T
he predicate function is often given as a lambda expression, which in ML is defined exactly like a function, except with the fn reserved word, instead of fun, and of course the lambda expression is nameless.

29. What is a curried function?
Answer:
Curried functions are interesting and useful because new functions can be constructed from them by partial evaluation.

30. What does partial evaluation mean?
Answer:
Partial evaluation means that the function is evaluated with actual parameters for one or more of the leftmost formal parameters.

31. Define reader macros.
Answer:
Reader macros or read macros, that are expanded during the reader phase of a LISP language processor. A reader macro expands a specific character into a string of LISP code. For example, the apostrophe in LISP is a read macro that expands to a call to QUOTE. Users can define their own reader macros to create other shorthand constructs.

32.What is the use of evaluation environment table?
Answer:
A table called the evaluation environment stores the names of all implicitly and explicitly declared identifiers in a program, along with their types. This is like a run-time symbol table. When an identifier is declared, either implicitly or explicitly, it is placed in the evaluation environment.

33. Explain the process of currying.
Answer:
The process of currying replaces a function with more than one parameter with a function with one parameter that returns a function that takes the other parameters of the initial function.


Problem Set

6. Refer to a book on Haskell programming and discuss the features of Haskell
Answer:
Haskell features lazy evaluation, pattern matching, list comprehension, type classes, and type polymorphism.Lazy evaluation or call-by-need is an evaluation strategy which delays the evaluation of an expression until its value is needed (non-strict evaluation) and which also avoids repeated evaluations (sharing). The sharing can reduce the running time of certain functions by an exponential factor over other non-strict evaluation strategies, such as call-by-name.Pattern matching is the act of checking a perceived sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually has to be exact. The patterns generally have the form of either sequences or tree structures. Uses of pattern matching include outputting the locations (if any) of a pattern within a token sequence, to output some component of the matched pattern, and to substitute the matching pattern with some other token sequence.List comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical set-builder notation (set comprehension) as distinct from the use of map and filter functions.Type class is a type system construct that supports ad-hoc polymorphism. This is achieved by adding constraints to type variables in parametrically polymorphic types. Such a constraint typically involves a type class T and a type variable a, and means that a can only be instantiated to a type whose members support the overloaded operations associated with T.Polymorphism is a programming language feature that allows values of different data types to be handled using a uniform interface.

7. What features make F# unique when compared to other languages?
Answer:
F# has a full-featured IDE, an extensive library of utilities that supports imperative, object-oriented, and functional programming, and has interoperability with a collection of nonfunctional languages. F# includes a variety of data types. Among these are tuples, like those of Python and the functional languages ML and Haskell, lists, discriminated unions, an expansion of ML’s unions, and records, like those of ML, which are like tuples except the components are named. F# has both mutable and immutable arrays.

8.How is the functional operator pipeline(|>)used in F#?
Answer:
The pipeline operator is a binary operator that sends the value of its left operand, which is an expression, to the last parameter of the function call, which is the right operand. It is used to chain together function calls while flowing the data being processed to each call. Consider the following example code, which uses the high-order functions filter and map:

let myNums = [1; 2; 3; 4; 5]

let evensTimesFive = myNums

|> List.filter (fun n −> n % 2 = 0)

|> List.map (fun n −> 5 * n)



Special thanks to Mr. Tri Djoko Wahjono, Ir., M.Sc.