1. Alternative Programming Paradigms
Chapter 8
Alternative Programming Paradigms

2. Paradigm
A paradigm is a model or mental framework for representing or thinking about something.
Programming in a procedural language consists of:
Planning the algorithm
Capturing the “unambiguous and effectively computable operations” as program instructions
Alternative paradigms for programming languages include viewing a program’s actions as:
A combination of various transform upon items (functional programming)
A series of logical deductions from known facts (logic programming)
Multiple copies of the same subtask or multiple subtasks of the same problem being performed simultaneously by different processors (parallel programming)

3. Functional Programming
LISP (LISt Processing)
FP (Functional Programming)
A functional programming language views every task in terms of functions.
Here ‘function’ means something like a mathematical function – a recipe for taking an argument and doing something with them to compute a single value.
Example: the function f(x)=2x transform the argument 3 into 6.

4. Primitive Functions
Certain functions, called primitive functions or just primitives, are defined as part of the language.
Other functions can be defined and named by the programmer.
Example: (using Scheme, a functional programming language derived from LISP) (define (double x) (* 2 x))
(define (square x) (* x x)) (define (polynomial x) (double (square x))
Also called applicative languages.

5. LISP LISP processes lists of things.
The argument to functions are often lists.
nil: empty list
(list 3 4 5)
(car (list 3 4 5)) returns 3
(cdr (list 3 4 5)) returns (4 5)

6. Adding Non-negative Integers
(define (adder input-list) (cond ((null? input-list) 0) (else (+ (car input-list) (adder (cdr input-list))))))
(adder (list (3 4 5))) returns 12
adder is a Recursive function
A functional language allows for clarity of thought; data values are transformed by flowing through a string of mathematical functions.
Adds another layer of abstraction to the programmer.

7. Logic Programming
Various facts are asserted to be true, and on the basis of these facts, a logic program can infer or deduce other facts.
When a query (a question) is posed to the program, it begins with the storehouse of facts and attempt to apply logic deductions, in as efficient a manner as possible, to answer the query.
Sometimes called declarative languages because their programs, instead of issuing commands to do something, make declarations or assertions that various facts are true.
Used to write expert systems.

8. Prolog PROgramming in LOGic
Originally intended as a tool for natural language processing
Prolog programs consist of facts and rules.
A fact expresses a property about a single object or a relationship among several objects.
Examples: president(lincoln,civil_war) before(fdr, kennedy)

9. Examples A query: ?-before(lincoln,fdr) will return Yes.
?-president(loncoln,civil_war),before(lincoln,fdr)
?-president(lincoln,X) X is a variable in Prolog (variables must begin with upper-case letters)
Derive new facts:
precedes(X,Y) if before(X,Y)
precedes(X,Y) if before(X,Z) and precedes(Z,Y)

10. Prolog Rules A prolog rule is a declaration of an “if A then B” form
Example: precedes(X,Y) :- before(X,Y) precedes(X,Y) :- before(X,Z), precedes(Z,Y)
Figure 8.12: A Prolog Program
earlier(X,Y) :- president(R,X),president(S,Y),precedes(R,S)

11. The Logic Programming Paradigm
Facts
Rules
Knowledge
base
Inference Engine
Query
Response

12. Parallel Programming “Grand Challenge” computing problems
SIMD: single instruction, multiple data stream
MIMD: multiple instruction, multiple data stream