Unit1 principle of programming language

UNIT 1

By-
Garima Jain

 Programming Language: Definition, History ,Feature
 Issues in Language Design
 Structure and Operation of Computer
 Programming Language Paradigms
 Efficiency, Regularity
 Issues in Language Translation
 Syntax and Semantics

 Definition : A notation of a algorithm and data
structures are called a programming language.

 To improve your ability to develop effective
algorithms
 To improve your use of existing programming
languages
 To increase your vocabulary of useful programming
constructs
 To allow a better choice of programming language
 To make it easier to learn a new language
 To make it easier to design a new language

 1951- 55: Experimental use of expression
compilers.
 1956- 60: FORTRAN, COBOL, LISP, Algol 60.
 1961- 65: APL notation, Algol 60 (revised),
SNOBOL, CPL.
 1966- 70: APL, SNOBOL 4, FORTRAN 66,
BASIC, SIMULA, Algol 68, Algol-W, BCPL.
 1971- 75: Pascal, PL/1 (Standard), C, Scheme,
Prolog.
 1976- 80: Smalltalk, Ada, FORTRAN 77, ML.

 1981- 85: Smalltalk-80, Prolog, Ada 83.
 1986- 90: C++, SML, Haskell.
 1991- 95: Ada 95, TCL, Perl.
 1996- 2000: Java.
 2000- 05: C#, Python, Ruby, Scala.

Numerically based languages
Computing mathematical expressions
FORTRAN, Algol, Pascal, PL/1, BASIC, C, C++

Business languages
COBOL (Common Business Oriented Language)
English-like notation

Artificial intelligence languages
Tree search; Rule-based paradigm
LISP (LISt Processing)
PROLOG (PROgramming in LOGic)
System languages
C, C++
Script languages: AWK, Perl, TCL/TK
Web programming: HTML, XML, Java,
Microsoft *.NET family

Batch processing (batches of files)
Interactive processing (time sharing)
Effects on language design
File I/O in batch processing
Error handling in batch processing
Time constraints in interactive processing

Interactive processing
Embedded system environments

No need for time sharing
Good interactive graphics
Non-standard I/O devices for embedded systems

Client-server model of computing
Server: a program that provides information
Client - a program that requests information
Interaction between the client and server programs
Active web pages, Security issues, Performance

 Conceptual integrity
 Orthogonality
 Naturalness for the application
 Support for abstraction
 Ease of program verification
 Programming environment
 Portability of programs
 Cost of use
 Cost of execution.
 Cost of program translation.
 Cost of program creation, testing, and use.
 Cost of program maintenance.

 Design to
 Run efficiently : early languages
 Easy to write correctly : new languages
 Data typing features in ML
 Class of C++
 Package of Ada

 A computer is an integrated set of algorithms and
data structures capable of storing and executing
programs.
 Hardware computer or
 virtual computer

•Well-known computer architecture: Von Neumann
• Imperative languages, most dominant, because of
von Neumann computers
– Data and programs stored in memory
– Memory is separate from CPU
– Instructions and data are piped from memory to
CPU
– Basis for imperative languages
• Variables model memory cells
• Assignment statements model piping
• Iteration is efficient

 Hardware realization
 Physical devices
 Firmware realization
 microprogramming
 Software simulation
 Some other programming language
 Combination of these techniques

 Data
 Various kinds of elementary and structured data.
 Primitive operations
 Sequence control
 Controlling the sequence of primitive operations
execution.

 Data access
 Controlling the data supplied to each execution of
an operation.
 Storage management
 Controlling the allocation of storage for programs
and data.
 Operating environment
 Providing mechanisms for communication with
an external environment containing programs and
data.

 Main memory
 High-speed register
 High-speed cache memory
 External files

Data and Program

 A set of build-in primitive operations
 Arithmetic operations on each built-in numeric
data (+,-,*,/)
 Testing various properties of data items (test for
zero, positive, and negative numbers)
 Accessing and modifying various parts of a data
item
 Controlling input-output devices
 Sequence control (jumps)

 There is an interpreter :
 Fetch the instruction
 Decode instruction
 Fetch designated operands
 Branch to designated operation
 Execute primitive operations 1 to n

Using an address register

 Access to operands of the operation

 Keeping all resources of the computer operating as
much as possible
 Memory
 Central processor
 External data devices

Multiprogramming
Cache memory

 The outside world of computer; a set of peripherals
and input-output devices

 Imperative / procedural languages
 Applicative / functional languages
 Rule-based / declarative languages
 Object-oriented languages

Statement oriented languages that change machine
state
(C, Pascal, FORTRAN, COBOL)
Computation: a sequence of machine states (contents
of memory)
Syntax: S1, S2, S3, ... where S1, S2, … are statements

Programming consists of building the function that
computes the answer
Computation: Function composition is major
operation (ML, LISP)
Syntax: P1(P2(P3(X)))

Computation: Actions are specified by rules that
check for the presence of certain enabling conditions.
(Prolog)
The order of execution is determined by the enabling
conditions, not by the order of the statements.
Syntax: Condition  Action

Imperative languages that merge applicative design
with imperative statements (Java, C++, Smalltalk)

Syntax: Set of objects (classes) containing data
(imperative concepts) and methods (applicative
concepts)

 Programming language Syntax
 Key criteria concerning syntax
 Basic syntactic concepts
 Overall Program-Subprogram structure
 Stages in Translation
 Analysis of the source program
 Synthesis of the object program
 Bootstrapping

The syntax of a programming language describes the
structure of programs without any consideration of
their meaning.

Readability – a program is considered readable if the
algorithm and data are apparent by
inspection.
Write-ability – ease of writing the program.
Verifiability – ability to prove program
correctness (very difficult issue)
Translatability – ease of translating the program
into executable form.
Lack of ambiguity – the syntax should provide for
ease of avoiding ambiguous structures

 Character set – The alphabet of the language.
Several different character sets are used: ASCII,
EBCIDIC, Unicode
 Identifiers – strings of letters of digits usually
beginning with a letter
 Operator Symbols – +-*/
 Keywords or Reserved Words – used as a fixed part
of the syntax of a statement

 Noise words – optional words inserted into statements
to improve readability
 Comments – used to improve readability and for
documentation purposes. Comments are usually
enclosed by special markers
 Blanks – rules vary from language to language.
Usually only significant in literal strings

 Delimiters – used to denote the beginning and the
end of syntactic constructs
 Expressions – functions that access data objects in a
program and return a value
 Statements – these are the sentences of the language,
they describe a task to be performed

Separate subprogram definitions: Separate
compilation, linked at load time E.g. C/C++
Separate data definitions: General approach in
OOP.
Nested subprogram definitions: Subprogram
definitions appear as declarations within the main
program or other subprograms. E.g. Pascal

Separate interface definitions:
C/C++ header files
Data descriptions separated from executable
statements. A centralized data division contains all data
declarations. E.g. COBOL
Un-separated subprogram definitions: No syntactic
distinction between main program statements and
subprogram statements.
E.g. BASIC

 Analysis of the source program

 Synthesis of the object program

 Bootstrapping

Lexical analysis (scanning) – identifying the tokens of the
programming language: keywords, identifiers, constants
and other symbols

In the program
void main()
{ printf("Hello Worldn"); }
the tokens are

void, main, (, ), {, printf, (, "Hello Worldn", ), ;, }

Syntactic analysis (parsing) – determining the structure
of the program, as defined by the language grammar.

Semantic analysis - assigning meaning to the syntactic
structures

Example: int variable1;

meaning: 4 bytes for variable1 , a specific set of
operations to be used with variable1.

The semantic analysis builds the bridge between analysis and
synthesis.

Basic semantic tasks:

• Symbol–table maintenance
• Insertion of implicit information
• Error detection
• Macro processing

Result : an internal representation, suitable to be used for
code optimization and code generation.

Three main steps:

Optimization - Removing redundant statements

Code generation - generating assembler commands with
relative memory addresses for the separate program
modules - obtaining the object code of the program.

Linking and loading - resolving the addresses -
obtaining the executable code of the program.

Assembler code not optimized:
Intermediate code:
LOAD_R B
Temp1 = B + C
ADD_R C
Temp2 = Temp1 + D
STORE_R Temp1
A = Temp2
LOAD_R Temp1
ADD_R D
STORE_R Temp2
LOAD_R Temp2
STORE_R A
Statements in yellow
can be removed

The compiler for a given language can be written in
the same language.

• A program that translates some internal representation
into assembler code.

• The programmer manually re-writes the compiler into
the internal representation, using the algorithm that is
encoded into the compiler.

From there on the internal representation is translated into
assembler and then into machine language.

 Syntax: what the program looks like.
 Semantics: the meaning given to the various
syntactic constructs.

Example:
V: array [0..9] of integer;
int V[10];

Unit1 principle of programming language

Unit1 principle of programming language

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Unit1 principle of programming language