meljun cortes programming languages other programming paradigms

8/8/2019 MELJUN CORTES Programming Languages Other Programming Paradigms

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Other Programming Paradigms

Programming Languages

* Property of STI

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Concurrent

Programming

It is a computer programming techniquethat provides for the execution of

operations concurrently, either with asingle computer or across a number ofsystems.

Single tasks are split into a number ofsubtasks that can be computed relatively

independently and then aggregated to forma single coherent solution.


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Reader-Writer Problem

The syntactic structure of tasks is similarto that of package, which also has two

basic parts: a specification part and a body . The specification part can contain “entry ”

statement only while the body contains thecorresponding “accept ” statement.

Local tasks become active when the parent

task reaches the “begin ” following the taskdeclaration.

The means of communication andsynchronization between tasks is achievedusing the concept of collecting between a

task issuing an entry call and a taskaccepting the call by an accept statement.


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with TEXT_IO; use TEXT_IO;

procedure READER_WRITER_TASK is

type ELEM is array(1…80) of CHARACTER;task READER_WRITER is

entry READ(V : out ELEM);

entry WRITE(E : in ELEM);

end;

task body READER_WRITER is

VARIABLE: ELEM; begin

accept WRITER(E : IN ELEM) do

VARIABLE:= E;

end;


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ontinuation…

loopselect

accept READ(V : out ELEM) do

V := VARIABLE;

end;

or

accept WRITE (E : in ELEM) do VARIABLE:=E;

end;

end select;

end loop

end READER_WRITER begin – -parent task

-- Statements that use the READER_WRITERin a meaningful way go here.

-- Note that this program will not terminate because of the infinite loop.

end READER_WRITER_TASK


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Delay Statement This statement suspends the execution of

the next statement in the applicationprogram for the specified period of time.

delay

Simple Timer

with TEXT_IO; use TEXT_IO;

procedure TIMER is

task MIN_TIMER

entry START;

entry STOP;

end MIN_TIMER;

task body MIN_TIMER is

begin

loopselect

accept START;

delay 60.0;

or

accept STOP;

orterminate;


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Delay Statement

ontinuation…

end selectend loop

end MIN_TIMER

begin

put (“Start timer ”);

MIN_TIMER.START; -- start the delay

-- sequence of statements that take lessthan one minute to execute.

MIN_TIMER.STOP;

-- the statements that follow cannot begin execution until one minute haselapsed.

putline (“”);

put (“End of Timer”)end TIMER

Task Termination

termination occurs when the task reachesthe end of its task body and all locally

declared tasks have terminated theirexecution


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Functional

Programming

It is a way of writing a program thatdescribes only the operations to be

performed on the inputs to the program.

LISP was proposed by John McCarthy1959 for symbolic programming language.

It was designed to implement modelcomputation.

In 1983, Common LISP was proposed byDARPA (Defense Advanced ResearchProjects Agency) for a standard design.

The values of LISP is called “S-expressions”or “symbolic expression”.

S-expressions can be a symbol, a number,or a list.


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Syntactic Elements

of LISP

The list of zero element is nil list or simplynil .

“Symbol” is a LISP term for name in the basic evaluator.

Nil is the false value and non-Nil value

represents true.

Atom is the basic syntactic element of LISPthat can be a number, a character, acontinuous stream of characters of stringsor nil .

Lists represent program and data at thesame time.


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LISP Interpreter

LISP interpreter completes the followingsteps:

Prompt user for input (only for interactivemode)

• Read list

• Evaluate list

• Print result

Continuous loop of the steps above

In evaluating an s-expression, several values are returned:

If the s-expression is a number, return the value of the number.

If the s-expression is an atomic symbol,

return the value bound to that symbol; if itis not bound, it is an error.

If the s-expression is a list, evaluate thesecond through the last arguments andapply the function indicated by the firstargument to the results.


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Controlling LISP

Evaluation

The constructs for controlling evaluation inLISP are

QUOTE

andEV L

.

To treat expressions as data, QUOTE isneeded to evaluate itself.

lisp> (quote (a b c))

(a b c)

lisp> (quote (+ 1 3))

(+ 1 3)

lisp> „ (a b c)

(a b c)

lisp> (list „(+ 1 2) „(+ 3))

((+ 1 2) (+ 3 4))

While QUOTE forces non-evaluation, EV Lobviously does the opposite.

lisp> (eval (+ 1 3))

4

lisp> (list eval (+ 1 2) eval (+ 3 4))(3 7)


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User-Defined Functions

General syntax for user-defined function:

(defun ( )

)

Example:

(defun cube (X)

(* x x x))

DEFUN does not evaluate its arguments, but defines a new function.


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Program Control LISP also has its statements for program

control which is different from evaluationcontrol.

COND

Conditions and actions are arbitraryexpressions.

cond ( )

( ). . .

( ))

Example of COND used in expression:

(defun absolute-value (x)

(cond ( (< x 0) (- x))

( (>= x 0) x)))


(cond ((< x 0) (- x))

(t x)))


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Program Control

IF-THEN-ELSE

This LISP construct works similarly with

other programming languages.

Example:


(if (< x 0) (- x) x))

(defun count (n)

(if (


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Operations on Lists

LISP as a list based programming languageis obviously designed for list operations.

Three basic list operations: CAR , CDR andCONS.

Given a list:

S, (S1,…,Sn), n>0, then (car S) is S1

From above, CAR is summarized as a listtruncation function that returns the firstelement of any given list.

CAR extracts the head or first element of anonempty list.

Example:

lisp> (car „(a b c))a


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Operations on Lists

Given a list:

S, (S1,…, Sn), n>0, then (cdr S) is(S2,…Sn)

CDR returns the elements of a list exceptthe first element.

Example:

lisp> (cdr „ (a b c))

(b c)

CDR extracts the tail, consisting all but thefirst element.

CAR and CDR are similar to stringmanipulation functions in C++ and VisualBasic. CAR can be used to list the elementsof a list while CDR can be used to get thelist of elements remaining excluding thefirst element.


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Operations on Lists

CONS operation build lists: creates value

with head and tail.

It can also be represented as a “dotted”notation. (a.x)

Given a list:

lisp> (cons 1 „(2 3 4))

(1 3 4)

this is the same as:

lisp> (car(1) cdr(2 3 4))

(1 3 4)


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Variables

Variable is a symbol denoting a quantity ora symbolic representation.

LISP has a function set with twoarguments:

it must be a symbol

it can be an expression that will beevaluated and the result bound to the

symbol (set „x 0)

The function setq serves as an easier

version because it does not try to evaluatethe first argument, and therefore, it doesnot need a quote. (setq x 0)

Variables exist in a global environment.However, if a value is bound to a symbolthat is used as formal parameter, theoriginal value will be restored when the

function returns.


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Local Variables

A local variable is declared inside a singlemethod and can be seen only by code

within that method.

The LET function allows specifying local variables

Syntax:

(let () )

with () ::=( )

Example:

(defun functionx (x y)

(let (a (b 3)

(setq a (* x y))

(- (* a x) b))))


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Local Variables

The following is a factorial function writtenin an iterative manner.

(defun fact (n)

(setf n! 1) ;

Initialization

(dotimes (I n n!) ; Loop

(setf n! (* n! (+ I 1))))) ; Body

The example below shows theimplementation of a function that removesan element from a list.

(defun without (el li)(cond ((null li) nil); Test if li is

empty

((equalp el (car li)) (cdr li))

(t (cons (car li) (without el (cdr

li))))))


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LISP Input/Output

Read is a predefined input function in

LISP.

Syntax:

(read STREAM)

The Read function acquires one LISPexpression as text from STREAM andreturns it as a LISP object.

If STREAM is nil, use the value of ‘standard-input’. STREAM or the value of ‘standard-

input’ may be a buffer, a marker, a function

or a string.

Example:

(read)

(setf x (read)) ; assigns theinput to x


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LISP Input/Output

The Print function is a predefined LISP

output function.

Syntax:

(print OBJ STREAM)

This function outputs the printedrepresentation of OBJECT to STREAM,

which prints in addition one newline beforethe object and another after it.

Example:

(print x)

(print (list x y z))

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