Proof of Correctness? ??

1
?? ?? ? ??

• ????
• Proof of Correctness? ??
• Lambda Calculus Python? ???? ?? ??
• ??? 2??? ???? 1? ??, term project? ??, ? ?? ????
  ? ?? ?? ??
• ??
• ??, ?? ? 12? ??? ????
• ??? 75?(1430-1545), ?? ???? ??

2
????

• Http//borame.cs.pusan.ac.kr/lecture
• ?????? (??)
• 2002? ?? ??
• 2002? ???, ?? ????
• 2003, 2004, 2005, 2006, 2007, 2008, 2009?, 2010,
  2011, 2012? ????
• ?? ???, ??, ?? ?? ??(??) ??
• ?? ?? ??? ? ?? ??? ??? ????? ?? ???? ??? ? ??

3
???? ??

• ??? ?? ???? ??? ???? ??? ?????
• ?????? ???? ? ?? ??? ?? ??? ???? ????, ???? ???
  (??? ????? ??)
• ?? ?????? ???? ??
• high-level data types built in, such as flexible
  arrays and dictionaries
• ???? ??? ?? ??? ???? ???, ??? ?????
• Runtime checking? ???

4
????? ??, ?? ?? ???

• Paul Graham? "Revenge of the Nerds"? "Beating for
  average"?? ??? ??? ?????, ????? ? ??? ? ??? ???
  ??? ??? ?? ??? ???? ??? ??? ????? ??? ????, ???
  ????? ??? ????? ??? ??? ? ??? ??? ??.?, ??? ? ??
  ??? ?? ??? ??? ???? ??? ? ??? ??? ????.
• GitHub JavaScript, Ruby, Python, PHP, Java, C,
  C, Perl, C, Objective C
• StackOverflow C, Java, PHP, JavaScript, C,
  Python, Objective-C, C, Ruby, Perl, Delphi

5
????? ?? ?? ?? (Script ?? ??)

• Tiobe.com (Skilled Engineer)
• Java 19.1
• C 15.2
• C 10.1
• PHP 8.7
• Visual Basic 8.4
• Perl 6.2
• Python 3.8
• C 3.7
• JavaScript 3.1
• Ruby 2.6
• Delphi 2.1

• Dice.com (2006?)
• Java 35.7
• C, C 15.3
• C 12.7
• Perl 11.9
• JavaScript 10.9
• Visual Basic .NET 5.2
• PHP 2.9
• Ajax 2.7
• Python 2.0
• Ruby 0.7

6
? ????? ???? ????

• ??? ????? ?? ? ??? ?? ??? ?? ?? ? ? ?? ??
• ???? ????? ??? ??? ???? ?? ????? ??? ? ?? ?
• ???? ????? ??? ??? ??? ??? ???? ??
• ????? ?? ? ???? ??? ??

7
????

• ??? ???? ??!! ??? ???? ??!!
• ??? ??(Object), ??? ??, ???
• ??? ??, ??
• ??? ??? ?? ??? ??? ???, ??? ???? ???
• ????? ???
• ??????? !!
• ??? ??? ???? ??? ? ?? ???? ??
• ??? ??? ?? ??(??? ??? ??)
• ??? ?? ????? ?? ? ???, ??? 1,000? ? ?? ????? ?? ?
  ??. (?? ??)
• ??? ?? ?? ??? ???? ????
• ??? ??? ???? ?? ????? ??? ?????? ??
• ??? ??? ??? ???? ? (?? ????? ? ???)

8
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?
• ?? ?? ??
• ????, ??, ???? ? ??
• ????, keywords, ??
• ????? ???? ??
• ??? ??? ? ??
• Implementation -- How a program executes

9
????? ??? ??

• 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

10
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

11
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.

12
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13
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

14
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

15
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? ??? ????? ???? ???? ?
  ??? ??

16
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, Cloud Computing

17
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

21
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

22
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

23
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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25
example1.f

• 234567 example1.f
  
• A tiny program to plot my running times
  using GrADS
• 
  
• PARAMETER(NDAYS365, UNDEF-9.99,
  EMPTY0.00)
• C
• REAL MIN(NDAYS)
• DIMENSION SEC(NDAYS)
• C
• CHARACTER27 HEADER
• CHARACTER3 DAY
• CHARACTER28 PATH
• C
• PATH'/data/temp4/alfredo/fortran/'
• C
• OPEN(1,FILEPATH//'runtimes.data',FORM'FORM
  ATTED',
• - STATUSOLD')

Changing to REAL
Nonexecutable
Sequential (by default)
26
example1.f
Undefined value

• READ (1,2) HEADER
• WRITE(,2) HEADER
• WRITE(,2) '----------------------------'
• C
• ND 0
• 1 CONTINUE
• ND ND1
• READ (1,3,END4) DAY,DATE,MIN(ND),SEC(ND)
  
• WRITE(,3) DAY,DATE,MIN(ND),SEC(ND)
• IF((MIN(ND).EQ.EMPTY).AND.(SEC(ND).EQ.EMP
  TY)) GO TO 4
• GO TO 1
• 4 CONTINUE
• ND ND - 1 !Taking away the last line
  because is blank
• CLOSE(1)
• 3 FORMAT(A3,2X,I8,2X,F5.2,2X,F5.2)
• WRITE(,)'---------------------------------
  ----------'
• WRITE(,)'I AM RUNNING SINCE JULY 1,
  2002!!!!!'
• WRITE(,)'THAT IS',ND,' DAYS AGO'
• C

runtimes.data DAY DATE MIN
SEC MON 01072002 -9.99 -9.99 TUE 02072002
-9.99 -9.99 WED 03072002 19.00 43.00 THU
04072002 19.00 33.00 FRI 05072002 19.00
33.00 SAT 06072002 19.00 27.00 SUN 07072002
-9.99 -9.99 MON 08072002 19.00 46.00
. . . TUE 15102002 29.00 7.00 WED 16102002
-9.99 -9.99 THU 17102002 FRI 18102002 SAT
19102002 SUN 20102002 MON 21102002 TUE
22102002 WED 23102002 THU 24102002 FRI
25102002 SAT 26102002 SUN 27102002
No value
27
example1.f

• OPEN(2,FILEPATH//'runtimes_gr.data',ACCESS
  'DIRECT',
• - STATUS'UNKNOWN',FORM'UNFORMATTED',R
  ECL1)
• C
• NDNOR 0
• NDSIR 0
• DO N 1, ND
• IF((MIN(N).EQ.UNDEF).OR.(SEC(N).EQ.UNDEF)
  ) THEN
• TIME UNDEF
• NDNOR NDNOR 1
• ELSE
• TIME MIN(N)SEC(N)/60.
• NDSIR NDSIR 1
• ENDIF
• WRITE(2,RECN) TIME
• ENDDO

28
example1.f

• WRITE(2,RECND1) UNDEF !Just adding 1 and
  2 extra
• WRITE(2,RECND2) UNDEF !blank lines for
  plotting purposes
• CLOSE(2)
• WRITE(,)'WELL,',NDSIR,' DAYS LEAVING FOR
  A RUN'
• WRITE(,)'AND',NDNOR,' DAYS JUST BEING
  LAZY'
• WRITE(,)'---------------------------------
  ----------'
• WRITE(,)'make ',ND2,' days in the script
  file'
• WRITE(,)'grads -blc "run runtimes.gs"'
• C
• 2 FORMAT(A27)
• C
• C f77 example1.f
• C ./a.out
• END

29
COBOL II

• 000010 IDENTIFICATION DIVISION.
• 000020 PROGRAM-ID. SAMPLE.
• 000030 AUTHOR. J.P.E. HODGSON.
• 000040 DATE-WRITTEN. 4 February 2000
• 000041
• 000042 A sample program just to show the form.
• 000043 The program copies its input to the
  output,
• 000044 and counts the number of records.
• 000045 At the end this number is printed.
• 000046 000050 ENVIRONMENT DIVISION.
• 000060 INPUT-OUTPUT SECTION.
• 000070 FILE-CONTROL.
• 000080 SELECT STUDENT-FILE ASSIGN TO
  SYSIN
• 000090 ORGANIZATION IS LINE
  SEQUENTIAL.
• 000100 SELECT PRINT-FILE ASSIGN TO
  SYSOUT
• 000110 ORGANIZATION IS LINE
  SEQUENTIAL.

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COBOL II

• 000120
• 000130 DATA DIVISION.
• 000140 FILE SECTION.
• 000150 FD STUDENT-FILE
• 000160 RECORD CONTAINS 43 CHARACTERS
• 000170 DATA RECORD IS STUDENT-IN.
• 000180 01 STUDENT-IN PIC X(43).
• 000190
• 000200 FD PRINT-FILE
• 000210 RECORD CONTAINS 80 CHARACTERS
• 000220 DATA RECORD IS PRINT-LINE.
• 000230 01 PRINT-LINE PIC X(80).
• 000240
• 000250 WORKING-STORAGE SECTION.
• 000260 01 DATA-REMAINS-SWITCH PIC X(2) VALUE
  SPACES.
• 000261 01 RECORDS-WRITTEN PIC 99.
• 000270

31
COBOL III

• 000270
• 000280 01 DETAIL-LINE.
• 000290 05 FILLER PIC X(7) VALUE SPACES.
  
• 000300 05 RECORD-IMAGE PIC X(43).
• 000310 05 FILLER PIC X(30) VALUE
  SPACES.
• 000311
• 000312 01 SUMMARY-LINE.
• 000313 05 FILLER PIC X(7) VALUE SPACES.
• 000314 05 TOTAL-READ PIC 99.
• 000315 05 FILLER PIC X VALUE SPACE.
• 000316 05 FILLER PIC X(17) VALUE
  'Records were read'.
• 000318 05 FILLER PIC X(53) VALUE SPACES.
• 000319

32
COBOL IV

• 000320 PROCEDURE DIVISION.
• 000330 PREPARE-SENIOR-REPORT.
• 000340 OPEN INPUT STUDENT-FILE.
• 000350 OUTPUT PRINT-FILE.
• 000351 MOVE ZERO TO RECORDS-WRITTEN.
• 000360 READ STUDENT-FILE
• 000370 AT END MOVE 'NO' TO
  DATA-REMAINS-SWITCH.
• 000380 END-READ.

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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 paradigms Python
• ??? ????, ?????? ??? ???? ???? ???? ??? ??? ????
  ??? ?????? ???? ??

38
??? ????!!

• (1) Orthogonality? C???? ???? ? ?? ??? ?? ???!
• (2)??? ???? ??? ? ????? ??? ??????
• (3) ????? ?????? Platform?? ?? ????? ??.
  Platform?? ????, ?? ??????? ?? ??? ???? ?? ??
  ??? smartphone platform? ????, ? platform? ??? ?
  ??? ???????? ???????(?)? ?? ??? ?? ? ?? ??? ????.