Introduction to Programming
Languages
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
What Is a Programming Lang¡uage
• A natural language is designed to
communicate between human
• A programming language is designed to
communicate between human and
computers
How we communicate
influences how we think,
and vice versa.
programming language is
a notation
for describing computation
in computer-readable and
human-readable form
Computation
• Computation is usually defined formally
using the mathematical concept of a Turing
machine
• Church's thesis states that it is not possible
to build a machine that is inherently more
powerful than a Turing machine
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
Levels of Programming¡ Languages
• Machine languages
• Assembly languages
• High-level languages
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
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.
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.
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Formal Defiriition 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
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
Compilers
Source
program
Input
Compiler
Target
program
Target
program
Output
Interpreters
Input
Source
program
Interpreter
Output
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
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
• Draw the common properties from all the
instances
› Adopt the essential properties from the whole
system
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
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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
control, such as loops, conditional
statements, and procedures
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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
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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, whilestatement, and procedures
• Unit abstractions: abstract data types such as
stacks, queues, trees, graphs
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Abstraction of Operations
High-Level Languages
Abstract Operations
Machine Operations
Machine Languages
25,
Abstraction of Operations
High-Level Languages
Abstract Operations
Machine Operations
Machine Languages
25,
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
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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;
2
Object-Oriented Programming
public cl.ass IntWithGcd
privats int value;
public 1ntWithGcd(int val) value val;
publlC int intVaIue() return value;
public int gcd(int v)
int z = value; int y = v;
,
wlailc (y != 0)
int t u *» v; z y; y t;
return z;
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Functional Programming
u
l$ V
0;
gcd(u, v)
gcd (v, u
gcd u v
v), otherwise.
if v
0 thela u
else gcd(v (u ’mod v))
Logic Programming
. gcd(U, V)
U
’.. gcd(U, V)
X
V es 0, Y
U O«V, gcd(V, Y)
gcd(U, V, U) •- V
0.
gcd(U, V, X) :- not (V = 0),
,
Y is U mod V,
gcd(V, Y, X).
X
Language Design Criteria ?
• It is very difficult to o0er 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 di0erent reasons
• Programming language design is a goalorientd activity
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
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
Generali T
• Do constructs haye 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
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
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
Other Criteria
• Consistent with accepted notations. (Most
languages today, but not APL)
• Restrictability: a programmer can program
ePectively in a subset of the full language.
(C++: avoids runtime penalties)
Other Criteria
• Consistent with accepted notations. (Most
languages today, but not APL)
• Restrictability: a programmer can program
ePectively in a subset of the full language.
(C++: avoids runtime penalties)
Other Criteria
• Consistent with accepted notations. (Most
languages today, but not APL)
• Restrictability: a programmer can program
ePectively in a subset of the full language.
(C++: avoids runtime penalties)
C++: A Case Study
• Thanks to Bjarne Stroustrup, C++ is not
only a great success story, but also the
best-documented language development
e0ort in history:
1997: The C+-r 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).
Course Contents
• Introduction
• Syntax
• Functional programming
• Logic programming
• Basic semantics
• Data types
• Expressions
• Statements
• Procedures
• Modules
• Exceptions
•ConcIusion
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