Programming language paradigm

1. Programming Language
Paradigms
Chapter 1
Language Design Issues

2. Why Study Programming Language?
1. To improve ability to develop effective
algorithms:
– Many languages provide features that when used
properly are of benefit to programmer but when use
improperly may west large amount of computer time,
consuming logical errors.
– Even programmer who has used a language for years
may not understand features.
– A typical example is recursion.
– New programming methods are constantly being
introduced in the literature.
– Use of best concept like object oriented programming,
logical programming or concepts.

3. Why Study Programming Language?
(cont.)
2. To improve your use of your existing
programming language:
– By understanding how features in your language
are implemented, greatly increase your ability to
write efficient program.
– For example understanding how data in array,
string or records are created and manipulated, by
understanding class, objects or recursion you can
build more efficient program.

4. Why Study Programming Language?
(cont.)
3. To allow better choice of programming
language:
– Knowledge of variety of languages may allow the
choice of just language for particular project,
there by reducing required coding efforts.
4. To make it easier to learn a new language:
– Varity of programming language constructs and
implementation techniques allows the
programmer to learn a new programming
language more easily.

5. Why Study Programming Language?
(cont.)
5. To make easier to design a new language:
– For programmer who think of themselves as
designers can need to have deep understanding
of basic languages.
– For example many new languages are based on c
or pascal as implementation models. This aspect
of program design is often simplified if the
programmer is familiar with a variety of
constructs and implementation methods from
ordinary programming language.

6. What is Programming Language?
• A language designed for programming
computers.
• A programming language is an artificial
language designed to communicate
instructions to a machine, particularly a
computer. Programming languages can be
used to create programs that control the
behavior of a machine and/or to express
algorithms precisely.

7. What is Programming Language?
• Programming languages are essentially
carefully designed notations.
• Programming language use to specify,
organize different aspect of problem solving.
• The designer of programming languages have
twin goal:
– Making computing convenient for people
– Making efficient use of computing machine.

8. Evolution of software Architecture
• Evolution of software is a step by step process

9. Evolution of software Architecture
(cont.)
• The computing industry has now entered in
third major era in the development of
computer program.
• For certain class of problem certain software
or languages are defined which is tested,
modified and used with minimum investment.
• Smalltalk and Perl are cost effective in that the
overall time and effort expended in solving a
problem on computer.

10. Evolution of software Architecture
(cont.)
• Maintenance:
– Evolution of software also include maintenance, as
studies have shown that the largest cost involved in
any program that is used over a period of year is not
the cost of initial design, coding and testing of
program but total life cycle costs include development
as well as maintenance.
– Maintenance includes repair error, changes in
program if required as the underlying hardware or
operating system is updated and extension and
enhancement of program.

11. Attributes of language
• Syntax and Semantics:
– The Syntax of a programming language is what the
program looks like.
– The Semantics of a programming language is the
meaning given to the various syntactic constructs.
– For example in C to declare vector V, of integers
• Int v[10]
– In contrast in Pascal specified as
• V array[0…9]of integer
– Although they create same object at run time, their
syntax is different

12. Language Paradigms
• There are four basic computational models
that describe most programming today
– Imperative
– Applicative
– Rule based
– Object Oriented

13. Language Paradigms
• Imperative languages:
– Imperative or procedural languages are command
driven or statement oriented languages.
– The basic concept is the machine state the set of
all values for all memory locations in the
computer.
– A program consists of a sequence of statements
and the execution of each statements cause the
computer to change the value of one or more
locations in its memory that is enter a new state.

14. Language Paradigms
• The syntax of such languages generally has the
form
• Statment1;
• Statmenet2;
• Applicative language:
– An alternative view of the computation performed
by a programming language is to look at the
function that the program represents rather than
just the stat changes as the program executes,
statement by statement.

15. Language Paradigms - Applicative
language
• In applicative language rather than looking at sequence
of states that the machine must pass through in
achieving an answer the question to be asked is what is
the function that must be applied to initial machine
state by accessing initial data.
• We can view this model as a lens that takes the initial
data and by manipulating the view of memory,
produce the desired answer.
• Program development proceeds by developing
functions from previously developed functions to build
more complex function.

16. Language Paradigms – Rule based
language
• Rule based languages execute by checking for the
presence of certain enabling condition and when
present, executing an appropriate action the
most common rule based language is prolog also
called a logic programming language.
• Enabling conditions determine the order of
execution
• The syntax is
– Enabling condition  action1
– Enabling condition  action2

17. Language Paradigms – Object Oriented
Programming
• Object Oriented Programming: In this case
complex data object are build , then a limited
set of functions are designed to operate on
those data.
• Complex object are designed as execution of
simple objects, inheriting property of simpler
objects.

18. Language standardization
• The need for standards - to increase
portability of programs
• Problem: When to standardize a language?
• If too late - many incompatible versions
• If too early - no experience with language
• Problem: What happens with the software
developed before the standardization?
• Ideally, new standards have to be compatible
with older standards.

19. Internationalization
• How to specify languages useful in a
global economy?
• What character codes to use?
• Collating sequences? - How do you
alphabetize various languages?
• Dates? - What date is 10/12/01?
10-12-01? 12.10.01 ?
Is it a date in October or
December?

20. Internationalization
• Time? - How do you handle
• time zones,
• summer time in Europe,
• daylight savings time in US,
• Southern hemisphere is 6 months out of phase
with northern hemisphere,
• the date to change from summer to standard
time is not consistent.
• Currency? - How to handle dollars, pounds,
marks, francs, euros, etc.

21. Timeliness
• One important issue is when to standardize a language.
FORTRAN was initially standardized in 1966 after there
were many incompatible version.
• This lead a problem because each implementation is
different from others.
• At the other extreme Ada was standardized in 1983 before
there were any implementations
• When it was not clear weather the language would even
work.
• The first effective Ada compiler did not appear until 1987
• C and Pascal were standardized while growing and before
there were too many incompatible version.

22. Programming environments
Programming environment is where programs are
created, tested.
Usually consists of support tools and command
language for invoking them
Typical tools include:
•editors
•debuggers
•verifiers
•pretty printers
•test data generators

23. Effects on language design
Programming environments have had two
large effects on language design:
• Features aiding separate
compilation/assembly from
components
• Features aiding program testing and
debuggin

24. Effects on Language Design
Separate compilation:
•For large programs, different programmers will be working on
separate parts.
•This requires a language that can compile the parts and merge
together later
•Separate compilation can be difficult because subprograms might
need each other
•There are ways to provide information to subprograms during
separate compilation:
•Information may need to be redeclared (FORTRAN)
•An order of compilation may be required (Ada)
•A library containing relevant specifications may be required
(Java/C++)

25. Effects on Language Design
•Option 1 above uses independent compilation. The subprogram is entirely self
contained.
•The disadvantage is inability to check inconsistency of data between external
declaration and internal re declaration. You will have assembly errors even though the
subprograms may have 0 errors.
•Options 2 and 3 require the use of libraries. The body is usually omitted during the
compilation of subprograms.
•Separate compilation has the side effect of enabling name collisions issues
•Several subprograms or portions of programs may have the same name
•This may not be determined until attempting to merge all subprograms
•There are three main ways languages avoid these name collisions
•Use of naming conventions (obligation is the programmer's)
•Use of scoping rules (Used by Pascal, C, Ada)
•Add name definitions from external library(inheritance in Object oriented)

26. Environment Frameworks
•Support environment: Uses infrastructure services called
environment framework
Environment framework: supplies data repository, GUI, security,
communication
•Ex: An environment framework would contain the following
A window manager such as Motif
VB and Visual Studio provide for libraries to build
windows