Chapter 15 of Concept of Programming Languages

Review Questions

2. What does a lambda expression specify?
The 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.

5. Explain why QUOTE is needed for a parameter that is a data list.
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?
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?
REPL stand for read-evaluate-print loop.

11. What are the two forms of DEFINE?
The simplest form of DEFINE is one used to bind a name to the value of an expression. This form is
(DEFINE symbol expression)
The general form of such a DEFINE is
(DEFINE (function_name parameters)
(expression)
)

13. Why are CAR and CDR so named?
The names of the CAR and CDR functions are peculiar at best. The origin of these names lies in the first implementation of LISP, which was on an IBM 704 computer. The 704’s memory words had two fields, named decrement and address, that were used in various operand addressing strategies. Each of
these fields could store a machine memory address. The 704 also included two machine instructions, also named CAR (contents of the address part of a register) and CDR (contents of the decrement part of a register), that extracted the associated fields. It was natural to use the two fields to store the two pointers
of a list node so that a memory word could neatly store a node. Using these conventions, the CAR and CDR instructions of the 704 provided efficient list selectors. The names carried over into the primitives of all dialects of LISP.

18. What is tail recursion? Why is it important to define functions that use recursion to specify repetition to be tail recursive?
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).

19. Why were imperative features added to most dialects of LISP?
LISP began as a pure functional language but soon acquired some important imperative features to increased its execution efficiency.

26. What is type inferencing, as used in ML?
Type inference refers to the automatic deduction of the type of an expression in a programming language. If some, but not all, type annotations are already present it is referred to as type reconstruction.

29. What is a curried function?
Curried functions a function which a new functions can be constructed from them by partial evaluation.

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

32. What is the use of the evaluation environment table?
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.

33. Explain the process of currying.
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.

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Problem Set


2 . Give a general form of function declaration in ML.
Function declarations in ML appear in the general form
fun function_name(formal parameters) = expression;

4. Refer to a book on Haskell programming and discuss the features of Haskell.
Haskell features lazy evaluation, pattern matching, list comprehension, type classes, and type polymorphism.

8. How is the functional operator pipeline (|>) used in F#?
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.

9. What does the following Scheme function do?
(define (y s lis)
(cond
((null? lis) ‘() )
((equal? s (car lis)) lis)
(else (y s (cdr lis)))
))
y returns the given list with leading elements removed up to but not including the first occurrence of the first given parameter.

10. What does the following Scheme function do?
(define (x lis)
(cond
((null? lis) 0)
((not (list? (car lis)))
(cond
((eq? (car lis) #f) (x (cdr lis)))
(else (+ 1 (x (cdr lis))))))
(else (+ (x (car lis)) (x (cdr lis))))
x returns the number of non-NIL atoms in the given list.