Programming Languages

1
Programming Languages

• Marjan Sirjani

2
2. 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

3
Major influences on designing a language

• The underlying computer which programs execute
  upon
• The execution model, or virtual computer that
  supports the language on the actual hardware
• The computational model that the language
  implements.

4
2.1. 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

5
Major Components of a Computer (From a
Programming Language Designers View)

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

6
Major Components of a Computer (From a
Programming Language Designers View)

• 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.

7
Data

• Main memory
• High-speed register
• High-speed cache memory
• External files
• Data and Program

8
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)

9
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

10
Data Access

• Access to operands of the operation

11
Storage Management

• Keeping all resources of the computer operating
  as much as possible
• Memory
• Central processor
• External data devices
• Multiprogramming
• Cache memory

12
Operating Environment

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

13
Computer States

• We saw the static organization of the
  computer,
• We also must see the dynamic operation of it
  during program execution.

14
Language Implementation

• Translation (compilation)
• Accept programs in some source language
• as input and produce functionally equivalent
  programs in another object language as output.
• Assembler assembly to machine language.
• Compiler a high level language to assembly or
  machine code.
• Loader,linker editor machine code in
  relocatable form to machine code really
  executable.
• Preprocessor a high level language to a high
  level language in a standard form .

15
Language Implementation

• Software simulation (interpretation)
• the simulator executes the input program
  directly.

16
Differences Between Software Implementations

• Translation versus Interpretation
• Physical input sequence
• Logical flow of control
• Process each program statement exactly once
• might process some statements repeatedly

17
Differences Between Software Implementations

• Faster program execution
• slow program execution
• Loss of information about program
• leaving statements in their original form
• Object program much larger then the source
  program
• no space is needed for object program

18
Firmware Computers

• A common alternative to the strict hardware
  realization of a computer is the firmware
  computer,
• simulated by a micro-program running on a
  special micro-programmable hardware computer.
• (emulation)

19
2.2. Virtual Computers

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

20
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 V10

21
Hierarchies of Computers
Virtual computer developed by programmer
The language virtual computer
Operating system virtual computer
Firmware virtual computer
Actual hardware computer
22
Binding and Binding Times

• Binding of a program element to a particular
  characteristic or property the choice of the
  property from a set of possible properties.
• Binding time of the property for that element
  the time during program formulation or processing
  when this choice is made.

23
Examples Of Binding

• Setting the value of an attribute
• A variable name , type, storage area
• A routine name formal parameters of a certain
  type, certain parameter-passing conventions,
• A statement associated actions.

24
Classes of Binding Times

• 1. Execution time (run time)
• (dynamic binding)
• 2. Translation time (compile time)
• 3. Language implementation time
• 4. Language definition time

25

• 1. Execution time
• On entry to subprogram or block.
• Binding of formal to actual parameters in C.
• At arbitrary points during execution .
• Binding of variables to values by assignments.
• (can be modified repeatedly during execution)

26

• 2. Translation time (compile time)
• Bindings chosen by the programmer
• Variable names and types
• Bindings chosen by the translator
• Relative locations of a data object in the
  storage allocated for a procedure
• Bindings chosen by the loader
• Actual addresses

27

• 3. Language implementation time
• The details associated with the representation of
  numbers and of arithmetic operations.
• (integer type memory representation)
• 4. Language definition time
• Possible statement forms, data structure types,
  program structures.
• (integer type definition)

28

• Programming languages differ in
• The number of entities with which they can deal,
• The number of attributes to be bound to
  attributes,
• The time at which such bindings occur (binding
  time),
• The stability of the binding (fixed or modifiable)

29
Importance of Binding Times

• Many of the most important differences among
  languages involve differences in binding times.
• Early binding efficiency.
• (FORTRAN types, arithmetic operations)
• Late binding flexibility.
• (ML types, string manipulations)

30
Binding Time An Example

• X X 10
• Set of possible types for variable X.
• Type of variable X.
• Set of possible values for variable X.
• Value of the variable.
• Representation of the constant 10.
• Properties of the operator .

31

• Attributes of a variable
• Name
• Scope
• Type
• L-value
• R-value

32
Name and Scope

• Static scope binding defines the scope in terms
  of the lexical structure of a program . (C,
  Pascal)
• Dynamic scope binding defines the scope of a
  variables name in term of program execution.
  (same dcl until new dcl)
• (APL, LISP, SNOBOL)

33
Name and Scope (dynamic binding)

• / block A/
• int x
• / block B/
• int x
• / block C/
• x

34
Type

• Static typing bind variables to their type at
  compile time, and the binding can not be changed
  during execution. Static type checking
• Dynamic typing run-time binding between
  variables and their types.
  (according to the value assigned)

35
2.3. Language Paradigms

• How does the program execute?
• What sort of constructs does the language
  provide?

36

• Four basic computational models
• Imperative languages
• Applicative language
• Rule-based language
• Object-oriented programming

37
Imperative Languages

• Imperative or procedural languages are
  command-driven or statement-oriented languages.
• Basic concept machine state.
• The syntax has the form like
• statement1
• statement2

38
Applicative Languages

• Applicative or functional languages look at the
  function that program represents rather than just
  to the state changes as the program executes,
  statement by statement.
• The syntax has the form like
• functionn(function2(function1 (data)))

39
Rule-based Languages

• Rule-based or logical languages execute by
  checking for the presence of a certain condition
  and when it is satisfied, they execute an
  appropriate action.
• The syntax has the form like
• enabling condition1 action1
• enabling condition2 action2
• enabling conditionn actionn

40
Object-Oriented Languages

• Object-oriented languages can be viewed as
  combining imperative and functional paradigms.
• Abstract data types
• inheritance
• efficiency of imperative languages
• flexibility and reliability of functional
  languages.

41
Generality of Computational Model

• How one uses a programming language depends on
  the programmer.