2. Presentation Outline
• 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
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4. Why study programming languages
• 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
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7. Language development
Numerically based languages
Computing mathematical expressions
FORTRAN, Algol, Pascal, PL/1, BASIC, C, C++
Business languages
COBOL (Common Business Oriented Language)
English-like notation
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8. Language development
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
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9. Software architectures
Mainframe era
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
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10. Software architectures
Personal computers
Interactive processing
Embedded system environments
Effects on language design
No need for time sharing
Good interactive graphics
Non-standard I/O devices for embedded systems
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11. Software architectures
Networking era
Client-server model of computing
Server: a program that provides information
Client - a program that requests information
Effects on language design
Interaction between the client and server programs
Active web pages, Security issues, Performance
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12. Attributes of a good language
• 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.
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13. Language Design Issues
• Design to
•Run efficiently : early languages
•Easy to write correctly : new languages
•Data typing features in ML
•Class of C++
•Package of Ada
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14. The Structure And Operation Of A
Computer
• A computer is an integrated set of algorithms and data structures capable
of storing and executing programs.
•Hardware computer or
•virtual computer
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15. Computer Architecture
•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
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17. Virtual Computers
• Hardware realization
•Physical devices
• Firmware realization
•microprogramming
• Software simulation
•Some other programming language
• Combination of these techniques
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18. Major Components of a Computer
• Data
•Various kinds of elementary and structured data.
• Primitive operations
• Sequence control
•Controlling the sequence of primitive operations
execution.
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19. Major Components of a Computer
• 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.
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20. Data
• Main memory
• High-speed register
• High-speed cache memory
• External files
Data and Program
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21. Operations
• 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)
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22. Sequence Control
• 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
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24. Storage Management
• Keeping all resources of the computer operating as much as possible
•Memory
•Central processor
•External data devices
Multiprogramming
Cache memory
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25. Operating Environment
• The outside world of computer; a set of peripherals and
input-output devices
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26. Language Paradigms
• Imperative / procedural languages
• Applicative / functional languages
• Rule-based / declarative languages
• Object-oriented languages
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27. Imperative / procedural 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
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28. Applicative / functional languages
Programming consists of building the function that
computes the answer
Computation: Function composition is major
operation (ML, LISP)
Syntax: P1(P2(P3(X)))
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29. Rule-based / declarative languages
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
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30. Object-oriented languages
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)
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31. Language Translation issues
•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
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32. Syntax
The syntax of a programming language describes the
structure of programs without any consideration of
their meaning.
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33. Key criteria concerning syntax
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
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34. Basic Syntactic Concepts
• 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
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35. Basic Syntactic Concepts
• 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
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36. Basic Syntactic Concepts
• 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
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37. Overall Program-Subprogram
Structure
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
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38. Overall Program-Subprogram
Structure
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
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39. Stages in Translation
• Analysis of the source program
• Synthesis of the object program
• Bootstrapping
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40. Analysis of the source program
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", ), ;, }
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41. Syntactic and Semantic Analysis
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.
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42. Basic Semantic Tasks
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.
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43. Synthesis of the object program
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.
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44. Optimization example
Intermediate code:
Temp1 = B + C
Temp2 = Temp1 + D
A = Temp2
Assembler code not optimized:
LOAD_R B
ADD_R C
STORE_R Temp1
LOAD_R Temp1
ADD_R D
STORE_R Temp2
LOAD_R Temp2
STORE_R A
Statements in yellow
can be removed
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45. Bootstrapping
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.
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46. Syntax and Semantics
• 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];
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