Chapter 8

1. 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