PPL UNIT 6
Q.1) Describe Functional Programming. Enlist its features. Also
list the commonly used functional programming languages. [6
Marks]
Answer: Functional Programming (FP) is a programming style where
programs are built using pure functions and immutable data.
It focuses on what to solve, not how to solve.
It avoids changing data and using loops; instead, it uses functions, recursion,
and expressions.
Features of Functional Programming:
Trick: SHIP that sails with PURE functions
Letter Feature
Pure functions (no side effects): Same input always gives same output, no
P
side effects.
U Uses recursion: Replaces loops using function calls.
R Referential transparency
E Expressions over statements
S Stateless (no variable changes): Doesn’t change external state or variables.
H Higher-order functions: Functions that take or return other functions.
I Immutable data: Variables are not changed once set
Pass functions as arguments (First-class): Functions can be passed as
P
arguments or returned.
Commonly Used Functional Programming Languages: Haskell, Lisp, Erlang,
Scala, F#, JavaScript (supports functional programming features), Python
(partially supports functional style).
Q.2) Describe Logical Programming. Enlist its features. Also list
the commonly used Logical programming languages. [6 Marks]
Answer: Logical Programming is a programming style based on formal
logic. In this approach, a program is written as a set of facts and rules, and the
computer uses logical reasoning to solve problems.
It focuses on what is true, not how to do it.
Trick: "Rule Based People Find Smart Answers"
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PPL UNIT 6
Features of Logical Programming:
Word Feature
Rule Rule-based programming: Uses facts and rules to reach conclusions.
Based Backtracking supported: Tries all possible options to find a solution.
People Pattern matching: Matches input data with known rules.
Formal logic-based (declarative style): Describes what to do, not how
Find
to do it.
Smart Symbolic computation: Works with symbols instead of numbers only.
Automatic inference engine: Solves queries using logical inference
Answers
engines.
Common Logical Programming Languages: Prolog (most popular logic
programming language), Datalog, Mercury, Answer Set Programming (ASP),
Absys.
Q.3) Explain the features of LISP programming. [6 Marks]
Answer: LISP stands for LISt Processing.
It is one of the oldest high-level programming languages, mainly used in
Artificial Intelligence (AI) and symbolic computation.
Features of LISP Programming:
🔹 1. Symbolic Expression Based:
LISP programs are written using S-expressions (symbolic expressions).
Code and data use the same structure: (operator operand1
operand2 ...)
🔹 2. List-Based Language:
Everything in LISP is stored and processed as a list.
Example: (+ 2 3) adds two numbers stored in a list.
🔹 3. Dynamic Typing:
Variables do not need to be declared with a type.
Data types are decided at runtime.
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PPL UNIT 6
🔹 4. Garbage Collection:
LISP has built-in automatic memory management, which removes
unused data.
🔹 5. Recursion Support:
LISP supports recursion strongly (functions calling themselves).
Recursion is used instead of loops.
🔹 6. Functional Programming Support:
Functions in LISP are first-class, meaning they can be passed as
arguments and returned from other functions.
Q.4) What is a predicate in LISP? Explain any 5 predicates with
example. [9 Marks]
Answer: In LISP, a predicate is a function that returns either T (true) or NIL
(false).
Predicates are used to test conditions in programs, especially in decision-
making (if, cond).
Predicate Purpose Example Output
atom Checks if value is an atom (not a list) (atom 'x) T
(atom '(1 2)) NIL
listp Checks if value is a list (listp '(a b c)) T
(listp 'x) NIL
numberp Checks if value is a number (numberp 5) T
(numberp 'a) NIL
symbolp Checks if value is a symbol (symbolp 'a) T
(symbolp 42) NIL
null Checks if value is NIL or empty list (null '()) T
(null '(a)) NIL
equal Checks if two values are equal (equal 4 4) T
(equal '(1 2) '(1
T
2))
Checks if two atoms are exactly the
eq (eq 'a 'a) T
same
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PPL UNIT 6
Predicate Purpose Example Output
(eq 'a 'b) NIL
zerop Checks if a number is zero (zerop 0) T
(zerop 5) NIL
evenp Checks if a number is even (evenp 4) T
(evenp 5) NIL
oddp Checks if a number is odd (oddp 3) T
(oddp 8) NIL
>, <, =, >=, Comparison predicates (greater,
(< 3 5) T
<= equal, etc.)
Q.5) What is Recursion? Write a LISP function to calculate
power of a number using recursion and iteration. [9 Marks]
Answer: Recursion is a programming technique where a function calls itself
to solve smaller versions of the same problem.
It continues until a base case is met.
1. Power Function using Recursion
(defun power-rec (base exp)
(if (= exp 0)
1
(* base (power-rec base (- exp 1)))))
Example: (power-rec 2 3) returns 8
2. Power Function using Iteration
(defun power-iter (base exp)
(let ((result 1))
(dotimes (i exp result)
(setf result (* result base)))))
📌 Example: (power-iter 2 3) returns 8
Explanation:
Recursive version: multiplies base with itself exp times using function
calls.
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PPL UNIT 6
Iterative version: uses a loop (dotimes) and a variable to multiply
repeatedly.
Q.6) Write a LISP program to find the factorial of n numbers
using recursion. [6 Marks]
Answer: LISP Code (Recursive Factorial):
(defun fact (n)
(if (= n 0)
1
(* n (fact (- n 1)))))
Example Call:
(print (fact 5)) ; Output: 120
Explanation (in simple words):
The function fact takes a number n.
If n is 0, it returns 1 (base case).
Else it multiplies n with fact(n - 1) (recursive step).
Q.7) Explain the following functions with suitable examples:
CAR(), CDR(), FIRST(). [6 Marks]
Answer:
1. CAR(): car is a LISP function that returns the first element of a list.
📌 Syntax: (car list)
📌 Example: (car '(a b c)) ; Output: a
2. CDR(): cdr returns the rest of the list after removing the first element.
Syntax: (cdr list)
Example: (cdr '(a b c)) ; Output: (b c)
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PPL UNIT 6
3. FIRST()
first is similar to car. It also returns the first element of a list.
It is part of Common LISP and often used for readability.
Example:
(first '(x y z)) ; Output: x
Q.8)
Q.*
Answer:
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PPL UNIT 6
Q.9) Explain with example how to use structures in Prolog. [9 M]
Answer: In Prolog, a structure is a compound term used to group related
data together.
It is like a record or object that has a name (functor) and one or more
arguments.
Syntax of Structure : functor(argument1, argument2, ..., argumentN).
The functor is the structure name, and arguments can be constants, variables,
or other structures.
Example 1: Representing a Student
student(john, 22, computer_engineering).
student(rahul, 20, electronics).
student is the structure name (functor)
john, 22, computer_engineering are the arguments
Example 2: Structure Inside a Structure:
address(city(pune), state(maharashtra)).
address is the main structure
city(pune) and state(maharashtra) are sub-structures
Q.10) What is a clause in Prolog? Explain types of clauses with
example. [9 Marks]
Answer: In Prolog, a clause is a basic building block of a program.
A clause represents a fact, rule, or goal in Prolog.
It is written in the form of:
head :- body.
Or simply:
fact.
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PPL UNIT 6
Types of Clauses in Prolog:
Prolog has 3 main types of clauses:
1. Fact (Unit Clause)
Represents a known truth.
It has no condition or body.
Example:
sun_rises_in(east).
likes(john, pizza).
2. Rule (Implication Clause)
Represents a condition-based logic.
Syntax: Head :- Body.
(Means: Head is true if Body is true)
Example:
happy(X) :- rich(X).
Means: X is happy if X is rich.
3. Goal (Query Clause)
Represents a question asked to the system.
Used by the user to find answers based on facts and rules.
Example:
?- likes(john, pizza).
Output: true
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