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Lambda Calculus, Proof of Correctness? ??

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Title: Lambda Calculus, Proof of Correctness? ??

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?? ?? ? ??

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Introduction

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Organization of Programming Languages

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Language Goals

During 1950s--1960s - Compile programs to execute
efficiently.
There is a direct connection between language
features and hardware - integers, reals, goto
statements
Programmers cheap Machines expensive Keep the
machine busy
But today
Compile programs that are built efficiently
CPU power and memory very cheap
Direct connection between language features and
design concepts - encapsulation, records,
inheritance, functionality, assertions
Event-driven programming, Service-oriented
approach, Web-service, Very High-level Language

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Python

Python is a general-purpose, high-level
programming language. Its design philosophy
emphasizes programmer productivity and code
readability. Python's core syntax and semantics
are minimalist, while the standard library is
large and comprehensive.
Python supports multiple programming paradigms
(primarily functional, object oriented and
imperative), and features a fully dynamic type
system and automatic memory management it is
thus similar to Perl, Ruby, Scheme, and Tcl.
Python was first released by Guido van Rossum in
1991.3 The language has an open,
community-based development model managed by the
non-profit Python Software Foundation. While
various parts of the language have formal
specifications and standards, the language as a
whole is not formally specified. The de facto
standard for the language is the CPython
implementation.

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Why study programming languages? (1)

To improve your ability to develop effective
algorithms
Improper use of recursion
Object-oriented programming, logic programming,
concurrent programming
To improve your use of your existing programming
language
Data structures for arrays, strings, lists,
records, set, bag, table (associative array)
Malloc() ? garbage collection
Implementation details of recursion, object
classes, subroutine calls, exception(event)
handling
Service-oriented developing
Web-service, Semantic web, Script language

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Why study programming languages? (2)

To increase your vocabulary of useful programming
constructs
Increase programming vocabulary and its
implementation tech.
Coroutine, Semaphore, event-driven programming,
associative array
Named parameter (keyword argument) (Ada, Python,
Smalltalk, Common Lisp)
Name mangling (name decoration) _Z on C, C
Filename mangling Unix file names can contain
colons or backslashes
To allow a better choice of programming language
Numeric computation C, FORTRAN, Ada
AI LISP, Prolog
Internet applications Perl, Java, HTML, XML,
Web Service(SOAP), PHP, ASP.net, Python

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Why study programming languages? (3)

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Evolution of software architecture

1950s - Large expensive mainframe computers ran
single programs (Batch processing)
1960s - Interactive programming (time-sharing) on
mainframes
1970s - Development of Minicomputers and first
microcomputers. Apple II. Early work on windows,
icons, and PCs at XEROX PARC
1980s - Personal computer - Microprocessor, IBM
PC and Apple Macintosh. Use of windows, icons and
mouse
1990s - Client-server computing - Networking, The
Internet, the World Wide Web
2000s - P2P, Grid Computing, Web Service,
Event-driven approach, Service-oriented
programming, Script language,

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Attributes of a good language (1)

Clarity, simplicity, and unity - provides both a
framework for thinking about algorithms and a
means of expressing those algorithms
Conceptual integrity
?? ? APL, SNOBOL4
Orthogonality - every combination of features is
meaningful
Fewer exceptions ? C???? !!!
Logical errors and inefficiency

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Attributes of a good language(2)

Naturalness for the application - program
structure reflects the logical structure of
algorithm
Sequential algorithm, concurrent algorithm, logic
algorithm, non-deterministic algorithm
Appropriate data structures, operations, control
structures, natural syntax
Support for abstraction - program data reflects
problem being solved
Data abstraction ltD,O,Cgt
Encapsulation

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Attributes of a good language (3)

Ease of program verification - verifying that
program correctly performs its required function
Verification/validation
standard, or specification requirements
the needs of the intended end-user or customer
Comments, assert()
Design specification
Programming environment - external support for
the language
Debugger, syntax-directed editor
Supporting function, platforms
Smalltalk
Supporting all the software lifecycle phases

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Attributes of a good language (continued)

Portability of programs - transportability of the
resulting programs from the computer on which
they are developed to other computer systems
Transportability
C, C, Pascal ? Java (Byte-code)
ML single source implementation
Cost of use - program execution, program
translation, program creation, and program
maintenance
Code optimization, (Smalltalk, Perl), lifecycle
costs

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Language paradigms

Imperative languages
Goal is to understand a machine state (set of
memory locations, each containing a value)
Statement oriented languages that change machine
state (C, Pascal, FORTRAN, COBOL, C, Java)
Syntax S1, S2, S3, ...
Applicative (functional) languages
Goal is to understand the function that produces
the answer
Function composition is major operation (ML,
LISP)
Syntax P1(P2(P3(X)))
Programming consists of building the function
that computes the answer

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Language paradigms (continued)

Rule-based languages
Specify rule that specifies problem solution
(Prolog, BNF Parsing)
Other examples Decision procedures, Grammar
rules (BNF)
Syntax Answer ? specification rule
Programming consists of specifying the attributes
of the answer
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)