Introduction to Programming Languages

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Introduction to Programming Languages

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

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Introduction
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Programming Languages

• Natural languages are designed to facilitate the
  communication between human
• Programming languages are designed to facilitate
  the communication between human and computers

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How we communicate influences how we think, and
vice versa.
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Study programming languages affects the way we
think about computers and computation.
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A programming language is a notation for
describing computation in computer-readable and
human-readable form
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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

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Levels of Programming Languages

• Machine languages
• Assembly languages
• High-level languages

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Computer-Readability

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

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Interpreters
Input
Source program
Output
Interpreter
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Compilers
Source program
Target program
Compiler
Target program
Output
Input
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Language Definitions

• The Syntax of a programming language specifies
  the structure of programs 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.

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Language Definitions

• The Semantics of a programming language specifies
  the meaning of programs 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.

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Language Definitions

• 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

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Human-Readability

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

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Abstract

• Disassociated from any specific instance (??)
• A summary of points (??)

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Abstractions
Data
Control
Operations
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Abstractions

• Data abstractions abstract properties of data,
  such as numbers, character strings, trees, which
  are subjects of computation
• Control abstractions abstract properties of the
  transfer of control, that is, the modification of
  the execution path of a program based on the
  situation at hand. Examples are loops,
  conditional statements, and procedure calls

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Data Abstractions

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

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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

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Abstraction of Operations
Basic data types
Basic statements
Structured data types
Structured statements
Abstract data types
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Abstraction of Operations
High-Level Languages
Abstract Operations
Machine Operations
Machine Languages
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Programming Paradigms

• Imperative programming a series of commands
  Fortran, Pascal, C, Ada
• Functional programming a collection of
  mathematical functions Lisp, ML, Haskell
• Logic programming a collection of logical
  declarations Prolog, Godel
• Object-oriented programming a collection of
  objects Simula, Smalltalk, C, Java

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Imperative Programming
int gcd(int u, int v) int t while (v
! 0) t u v u v
v t return u
How
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Functional Programming
gcd u 0 u gcd u v gcd (v (u mod
v)) gcd u v if v 0
then u else gcd(v (u
mod v))
What
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Logic Programming
gcd(U, V, U) - V 0. gcd(U, V, X) - not
(V 0), Y is U mod V, gcd(V, Y, X).
What
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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
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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

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Contents

• History
• Language design principles
• Syntax
• Imperative programming
• Functional programming
• Logic programming
• Object-oriented programming