Lambda Calculus, Proof of Correctness? ??

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Introduction

• Programming Language Design and Implementation
  (4th Edition)
• by T. Pratt and M. Zelkowitz
• Prentice Hall, 2001
• Sections 1-1.3.2

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Organization of Programming Languages

• Understand how languages are designed and
  implemented
• ??
• Lexicon What sorts of words are legal?
• Syntax -- What a program looks like?
• Semantics -- What a program means?
• Pragmatics ?? ???? ??? C??? int?
• Implementation -- How a program executes
• Understand most appropriate language for solving
  specific problems, For example
• Pascal, C, Perl -- procedural, statement oriented
• C, Java, Smalltalk -- Object oriented
• ML, Lisp -- Functional
• Prolog -- Rule-based
• JavaScript, PHP, ASP.net, C Procedural,
  Event-driven accessing

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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)

• To make it easier to learn a new language
• Web programming (JavaScript, PHP), Semantic web
• Python
• To make it easier to design a new language
• User interface design
• C, COBOL, SMALLTALK? ??? ????? ???? ???? ?
  ??? ??

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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)

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New Paradigm

• Internet, Home Computing, Ubiquitous Computing,
  Embedded Computing, etc
• Languages and Compilers that are smart, small and
  safe
• Moveable code ? agents
• Independent from machines and programming
  environments
• Supporting pragmatics or intelligence
• Java, XML, Mobile computing. Mobile code
• Event driven approach, Service-oriented
  Architecture, Web Service
• Supports multiple paradigm Python

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