Introduction to Programming Languages

1
Introduction to Programming Languages

• Nai-Wei Lin
• Department of Computer Science and Information
  Engineering
• National Chung Cheng University

2
Chapter 1Introduction
3
Outline

• What is a programming language
• Levels of programming languages
• Definition of programming languages
• Implementation of programming languages
• Abstractions in programming languages
• Paradigms of programming languages
• Language design principles

4
What Is a Programming Language

• A natural language is designed to communicate
  between human
• A programming language is designed to communicate
  between human and computers

5
How we communicate influences how we think, and
vice versa.
6
A programming language is a notation for
describing computation in computer-readable and
human-readable form
7
Computation

• Computation is usually defined formally using the
  mathematical concept of a Turing machine
• Churchs thesis states that it is not possible to
  build a machine that is inherently more powerful
  than a Turing machine

8
Turing Completeness

• A programming language is Turing complete if it
  can be used to describe all the computation that
  a Turing machine can perform
• A programming language is Turing complete if it
  has integer variables and arithmetic operators,
  assignment statements, sequence statements,
  selection statements, and iteration statements

9
Levels of Programming Languages

• Machine languages
• Assembly languages
• High-level languages

10
Definition of Programming Languages

• The Syntax of a programming language specifies
  the structure of programs
• The Semantics of a programming language specifies
  the meaning of programs

11
Syntax
An if-statement consists of the word if
followed by an expression inside parentheses,
followed by a statement, followed by an optional
else part consisting of the word else and
another statement.
12
Semantics
An if-statement is executed by first evaluating
its expression, which must have arithmetic or
pointer type, including all side effects, and if
it compares unequal to 0, the statement following
the expression is executed. If there is an else
part, and the expression is 0, the statement
following the else is executed.
13
Formal Definition of Programming Languages

• The Syntax of a programming language is usually
  formally defined by context-free grammars
• The Semantics of a programming language is
  usually informally defined by human languages. It
  can be partially defined in a formal language
  using operational semantics, denotational
  semantics, or axiomatic semantics

14
Implementation of Programming Languages

• A compiler is a program that can translate
  programs written in a language into programs
  written in another language
• An interpreter is a program that can understand a
  language and execute programs written in that
  language

15
Compilers
Target program
Compiler
Output
16
Interpreters
Interpreter
17
Virtual Machines

• An interpreter can be viewed as a virtual machine
  that can directly execute a high level
  programming language
• Compilers and interpreters are relative concepts.
  Many programming languages have both a compiler
  and an interpreter
• Java has a compiler that translates the Java
  programs into Java byte codes. The Java virtual
  machine is an interpreter that can directly
  execute Java byte codes

18
Abstractions in Programming Languages

• A programming language provides abstractions of
  the computation that are easy to understand, even
  by persons not familiar with the underlying
  details of the computer

19
Abstract
??
??

• Draw the common properties from all the instances
• Adopt the essential properties from the whole
  system

20
Abstractions
Data
Control
Operations
21
Abstractions

• Data abstractions abstract properties of data,
  such as numbers, character strings, trees, which
  are subjects of computation
• Control abstractions abstract properties of
  control, such as loops, conditional statements,
  and procedures

22
Data Abstractions

• Basic abstractions basic data types such as
  integers, floating point numbers, and characters
• Structured abstractions structured data types
  such as arrays and records
• Unit abstractions abstract data types such as
  stacks, queues, trees, and graphs

23
Control Abstractions

• Basic abstractions basic statements such as
  assignment statement and goto statement
• Structured abstractions structured statements
  such as if-statement, while-statement, and
  procedures
• Unit abstractions abstract data types such as
  stacks, queues, trees, graphs

24
Abstraction of Operations
Basic data types
Basic statements
Structured data types
Structured statements
Abstract data types
25
Abstraction of Operations
Machine Operations
Machine Languages
26
Paradigms of Programming Languages

• Imperative programming a series of commands
  Fortran, Pascal, C, Ada
• Object-oriented programming a class of objects
  Simula, Smalltalk, C, Java
• Functional programming a collection of
  mathematical function definitions Scheme, ML,
  Haskell
• Logic programming a collection of logical
  predicates Prolog, Godel

27
Imperative Programming
int gcd(int u, int v) int t while (v
! 0) t u v u v
v t return u
How
28
Object-Oriented Programming
public class IntWithGcd private int
value public IntWithGcd(int val) value
val public int intValue() return value
public int gcd(int v) int z
value int y v while (y ! 0)
int t u v z y y t
return z
How
29
Functional Programming
u , if v 0
gcd(u, v) gcd (v,
u v), otherwise.
gcd u v if v 0 then u
else gcd(v (u mod v))
What
30
Logic Programming
V 0 ? gcd(U, V) U V ? 0, Y U V,
gcd(V, Y) X ? gcd(U, V) X
gcd(U, V, U) - V 0. gcd(U, V, X) - not
(V 0), Y is U mod V, gcd(V, Y, X).
What
31
Language Design Criteria ?

• It is very difficult to offer criteria for good
  programming language design
• Criteria for good programming language design
  often conflict each other
• A programming language can be a success or
  failure for many different reasons
• Programming language design is a goal-orientd
  activity

32
Efficiency

• Efficiency of compiler construction
  implementability
• Efficiency of compiler execution simplicity,
  reliability
• Efficiency of program construction writability,
  expressiveness
• Efficiency of program execution optimizability
• Efficiency of program modification readability,
  maintainability

33
Regularity

• Regularity is a measure of how well a language
  integrates its features, so that there are no
  unusual restrictions, interactions, or behaviors
• Regularity can be placed in subcategories
  Generality, Orthogonality, Uniformity

34
Generality

• Do constructs have as few restrictions as
  possible?
• Functions
• In Pascal, functions can be passed as parameters,
  but there are no function variables.
• C lacks nested functions.
• Scheme and ML have completely general functions
• Fortran can pass variable-length array
  parameters, but cannot define variable-length
  array variables

35
Orthogonality

• Can constructs be combined in any meaningful way?
• Return types of functions
• In Pascal, functions can return only scalar or
  pointer types as values.
• In C and C, values of all types, except array
  types, can be returned.
• In Ada and functional languages, values of all
  types can be returned

36
Uniformity

• Do similar things look the same, and do different
  things look different?
• In C, a semicolon is necessary after a class
  definition but forbidden after a function
  definition
• In Pascal, returned values from functions look
  like assignments

37
Other Criteria

• Simplicity make things as simple as possible,
  but not simpler. (Pascal, C)
• Expressiveness make it possible to express
  conceptual abstractions directly and simply.
  (Scheme, Simula67)
• Extensibility allow the programmer to extend the
  language in various ways. (Scheme, C)

38
Other Criteria

• Security programs cannot do unexpected damage.
  (Pascal, Java)
• Preciseness having a definition that can answer
  programmers and implementers questions. (Most
  languages today, but only one has a mathematical
  definition ML)
• Machine-independence should run the same on any
  machine. (Java)

39
Other Criteria

• Consistent with accepted notations. (Most
  languages today, but not APL)
• Restrictability a programmer can program
  effectively in a subset of the full language.
  (C avoids runtime penalties)

40
C A Case Study

• Thanks to Bjarne Stroustrup, C is not only a
  great success story, but also the best-documented
  language development effort in history
• 1997 The C Programming Language, 3rd Edition
  (Addison-Wesley).
• 1994 The Design and Evolution of C
  (Addison-Wesley).
• 1993 A History of C 1979-1991, SIGPLAN Notices
  28(3).

41
Course Contents

• Introduction
• Syntax
• Functional programming
• Logic programming
• Basic semantics
• Data types

• Expressions
• Statements
• Procedures
• Modules
• Exceptions
• Conclusion