Modern Programming Languages

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Modern Programming Languages
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Computation

• Computation is an abstract and subtle mental
  notion
• With a concrete realization by a machine
• Causing electrons/photons to change
  states/configurations
• There are mathematical models of information
  Computation
• We could perhaps benefit from a philosophy of
  computation
• Effective transformation of inputs to outputs
• For the class of Turing computable functions
• effective procedures ? algorithms
• Symbolic (syntactic) rewriting based on
  well-defined rules (semantic) to compute an
  answer (pragmatics)
• mlgtfun gcd(m,n) if m 0 then n else gcd(n
  mod m, m)
• mlgtgcd(712,332)
• answer is 4
• A reconfiguration of bits (information) in the
  memory of some kind of abstract or real machine
• Which are then interpreted relative to some model
  of computation

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Algorithm

• The Art of Computer Programming (TAOCP), Vol. 1
  Fundamental Algorithms by D.E.Knuth
• Euclid of alexandria (BC 325 BC 265), Egypt
• Euclids Elements GCD algorithm
• Abu Jafar Muhammad ibn Musa Al-Khawarizmi (about
  780 850), lived in Baghdad, Persia

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Recent history

• Formal models of computation 1900 1936
• Churchs Thesis all represent same class of
  computations
• Freges concept script
• Churchs ?-calculus
• Kleenes recursive functions
• Turings abstract Computing machine
• Currys combinatory logic
• Posts production system
• Principal notations for describing computations
• TM alphabet of tape symbols, r/w tape, set of
  states, state transition functions, imperative
  control mechanism
• T (Q, S, I, q0 ,F) (q0 , q1 , q2 , q3 ,
  q4,0, 1, q0 , q4)
• Not programmer friendly
• ?-calculus ?-terms, abstractions, and reduction
  rules
• Expression evaluation by parameter substitutions
  reduction
• (?x.x1) 2 ? 21 ? 3
• Lacks many practical features for programming a
  real computer

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Logic, Turing Machine ?-calculus

• Churchs thesis tells us that all these
  formalisms describe the same class of
  mathematical objects
• i.e., the class o computable functions
• Choose the formalism best suited to the problem
• Turing Machines ? imperative programming
• Focus on explicit state transitions and
  assignment
• ?-calculus ? functional programming
• Pure expression evaluation and no assignment
• Predicate Logic ? logic programming
• Horn clause resolution

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Formalisms that have persisted

• Predicate logic
• Gottlöb Frege, 18481925
• Computation by logic deduction
• Formal basis for proof theory automated theorem
  proving
• ?-calculus
• Alonzo Church, 19031995
• Formal basis for all functional languages,
  semantics type theory
• Turing Machines
• Alan Turing, 19121954
• Formal basis for computational complexity theory
• Recursive Functions Automata
• Stephen Kleene, 19091994
• Formal basis for meta-mathematical theories
• Regular Expressions, Finite State machines,
  Push-Down Automata

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Formalisms that have faded

• Combinatory logic
• Haskell Curry, 19001982
• Post Production Systems
• Emil Post, 18971954

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What is a programming language?

• A Formal notation for specifying an infinite
  number of computations
• Always requires an unambiguous syntax for the
  language
• Specified by a finite context-free grammar
• Should have a well-defined compositional
  semantics for each syntactic construct in the
  language
• Axiomatic vs. denotational vs. operational vs.
  ad-hoc
• Often requires a practical implementation
  pragmatics
• General purpose language vs. domain specific
  language
• Implementation on a real machine vs. a virtual
  machine
• Efficiency vs. portability
• Transition vs. compilation vs. interpretation
• C was originally translated to C by
  B.Stroustrups cfront translator
• Gnus g was the first native-code C compiler
  (Michael Tieman)
• Java Originally used a byte-code interpreter, but
  then hust-in-time(JIT) compilers appeared, and
  now native code compilers are commonly used for
  greater run-time efficiency (Gosling, Ungar,
  Bothner)
• LISP, Scheme and most functional languages are
  interpreted by a virtual machine, but code is
  often pre-compiled to byte codes for efficiency

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Programming Paradigms

• Procedural/Imperative Programming
• FORTRAN, ALGOL, Pascal, C,
• Functional/Applicative Programming
• LISP, Scheme, ML, Haskell,
• Logic/Declarative Programming
• PROLOG,
• Object-oriented Programming
• C, Java, C,
• Hybrids
• Concurrent, parallel, dataflow, intensional,
  domain specific,
• Scripting, extension languages,

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Key language milestones

• Assembly languages
• Invented by machine designers in the early 1950s
• Shift from binary machine codes to mnemonics
• First occurrence of reusable macros subroutines
• FORTRAN FORmula TRANslation
• Designed by John Backus at IBM in the mid-1050s
• First high-level algebraic language with a
  compiler
• LISP LISt Processor
• Designed by John McCarthy in 1958
• First language to be based on the theory of
  recursive functions
• Influenced by Churchs ?-calculus notation
• Major influence on all subsequent functional
  languages
• As well as on Smalltalk

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FORTRAN

• John Backus (1924 )
• Turing Award 1977
• On FORTRAN We did not know what we wanted and
  how to do it. It just sort of grew. The first
  struggle was over what the language would look
  like. Then how to parse expressions - it was a
  big problem and what we did looks astonishingly
  clumsy now....
• BNF The syntax and semantics of the proposed
  international algebraic language of the Zuerich
  ACM-GRAMM conference. ICIP Paris, June 1959.
• Influenced by Chomskys work on context-free
  grammar

syntax rule rule identifier ""
expression expression term "" term
term factor factor factor
identifier quoted_symbol "(" expression ")"
"" expression "" "" expression ""
identifier letter letter digit
quoted_symbol """ any_character """
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LISP

• John McCarthy (1927 )
• 1971 Turing Award
• In the course of its development the LISP system
  went through several stages of simplification and
  eventually came to be based on a scheme for
  representing the partial recursive functions of a
  certain class of symbolic expressions.
• Recursive Functions of Symbolic Expressions and
  their Computation by Machine (Part I). CACM,
  April 1960.

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The roots of modern languages

• AlGOL 60 International Algorithmic Language
• Designed by IFIP WorkingGroup 2.1 in 1958-1960
• Earlier version IAL, ALGOL 58
• John Backus, Peter Naur, John NcCarthy, Alan
  Perlis others
• Formally specified syntax using Backus-Naur Form
  (BNF)
• Significant influence on all of todays modern
  languages
• Introduced explicit variable type declarations,
  block structure (begin-end), nested lexical
  scopes recursive procedures
• Pascal, Modula, Ada, C, C and Java are direct
  descendants of ALGOL
• Scheme adopted lexical scoping from ALGOL
• Revised Report on the Algorithmic Language Algol
  60
• Revised5 Report on the Algorithmic Language
  Scheme
• Simula 67 first object-oriented language
• Designed by Ole-Johan Dahl and Kristen Nygaard
• Influenced all subsequent OO programming
  languages
• Objects classes
• Inheritance (subtyping) virtual methods
  (subtype polymorphism)
• Note parametric polymorphism (generics) came
  from CLU

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ALGOL 60

• Backus, Mccarthy
• Alan Perlis, 19221990
• 1966 turing award (1st)
• Syntatic sugar causes cancer of the semi-colons

• Peter Naur (1928 )
• Editor Revised Report on the Algorithmic
  Language Algol 60
• BNF used as a meta-language for ormally
  describing the valid syntatic phrases of the
  language

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Simula

• Ole-Johan Dahl (1932 2002)
• Kristen Nygaard (1926 2002)
• Joint 2001 Turing Award
• Joint 2002 von Neumann Medal
• Simula I (1962-1965) and Simula 67 are the two
  first object-oriented languages.
• Simula 67 introduced most of the key concepts of
  object-oriented programming both objects and
  classed, subclasses (usually referred to as
  inheritance) and virtual procedures, combined
  with safe referencing and mechanisms for bringing
  into a program collections of program structures
  described under a common class heading (prefixed
  blocks)

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Other important languages

• ALGOL-like
• Jovial, Euler, Pascal, Algol-68, Forsythe, CLU,
  Ada
• OO
• Smalltalk, Objective-C, C, Eiffel, Modula-3,
  self, C
• Functional
• ISWIM, FP, SASL, Miranda, Haskell
• LCF, ML, SML, Caml OCAML
• Scheme, Common LISP, CLOS
• Logic
• PROLOG, Gödel, LDL, automated theorem provers
• Research-Oriented
• Dylan, ABCL/1, ACT and more and more ...

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Ada

• Primarily used by the US dept of Defense
• Designed by a French language design team as part
  of an open competition
• Named after Ada Byron (Lady Lovelace), 1815
  1851
• At a young age, Ada learned of Charles Babbages
  ideas for a new calculating engine, the
  Analytical Engine, He conjectured what if a
  calculating engine could not only foresee but
  could act on that foresight. Ada was impressed by
  the universality of this idea. She suggested the
  idea of writing a plan for how this new
  calculating engine could be used to calculate
  Bernoulli numbers. This plan, is now regarded as
  the first computer program.
• Ada, The Enchantress of Numbers, by Betty
  Alexandra Toole

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Application specific languages

• Commercial data processing
• COBOL, SQL, 4GLs
• Systems Programming
• PL/I, PL/M, BLISS, Modula, Modula-2, Oberon
• Specialized applications
• BASIC, APL, Forth, Icon, Logo, SNOBOL4, GPSS,
  VisualBasic
• Concurrent, Parallel Distributer
• Concurrent Pascal, Concurrent C, C, SR, Occam,
  Erlang, Obliq
• System administration
• Command shells sh, csh/tcsh, ksh/zsh, bash, ..
• Perl, PHP, python, Rexx, Ruby, Tcl,
• Programming tool (Mini languages)
• AWK, make, lex, yacc, autoconf,

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COBOL

• COmmon Business Oriented Language
• Invented in 1950s
• Primarily used for business data processing
  applications
• Billions spent to fix Y2K issues in old COBOL
  programs
• Admiral Grace Murray Hopper, 1906 1992
• Ph. D in Mathematics, Yale, 1934
• Joined the Navy in 1943 and worked at Harvard
  with Howard Aiken on the Mark I and Mark II
  computers
• Called the mother of COBOL for her
  contributions to the standardization of the
  language
• Grace Hopper Celebration of Women in Computing
• Grace Murray Hopper Award

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The First Computer Bug

• U.S. Naval Historical Center Photograph.Courtesy
  of the Naval Surface Warfare Center, Dahlgren,
  Va., 1988.
• In 1945, LTJG Grace Murray was working on the
  Harvard University Mark II Aiken Relay
  Calculator.  While testing Mark II due to a
  malfunction, a moth was found trapped between
  points at Relay 70, Panel F on 9 September.  The
  operators removed and affixed the moth to the
  computer log, with the entry  "First actual case
  of bug being found."  They put out the word that
  they had "debugged" the machine, thus introducing
  the term "debugging a computer program."
• Although, Hopper was always careful to admit that
  she was  not present when the moth was
  discovered, it was one of her favorite stories. 
• In 1988, the log, with the moth still taped by
  the entry, was found in the Naval Surface Warfare
  Center Computer Museum at Dahlgren, Va. 

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KR C, ISO/ANSI C

• Brian Kernighan
• Also the K in AWK
• Dennis Ritchie
• 1983 Turing award (with Ken Thompson)

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From C to C with classes to C

• Bjarne Stroustrup
• Ph.D unvi of Cambridge
• Used Simula in Ph. D. research and he knew about
  BCPL
• Then he went to Bell Labs created C with
  Classes in 1979
• in C due to A. Koenig
• First Cfront translator from C to C around
  1983
• An overview of the C programming Language

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And then came Java

• James Gosling (and Duke)
• Gosling Emacs
• The Green Project
• Oak ? Java
• Java is more influenced by C (syntax) and
  Modula-3 (object model) than by C
• Unlike C
• No operator overloading
• No templates
• No multiple inheritance
• Like Modula-3
• Explicit interfaces
• Single class inheritance
• Exception handling
• Built-in threading model
• Automatic garbage collection

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From BASIC to c to

• The un-Java for windows
• It is window-ized so that it is legally not java
• The politics of language adoption
• C had an interesting run-time environment
• .NET CLR common language run time for Visual
  Basic, C, C and future Microsoft languages.

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Why so many languages?

• EPIGRAMS IN PROGRAMMING by Alan Perlis
• 1. One man's constant is another man's variable.
• 2. Functions delay binding data structures
  induce binding. Moral Structure data late in the
  programming process.
• 3. Syntactic sugar causes cancer of the
  semicolon.
• 4. Every program is a part of some other program
  and rarely fits.
• 5. If a program manipulates a large amount of
  data, it does so in a small number of ways.
• 6. Symmetry is a complexity-reducing concept
  (co-routines include subroutines) seek it
  everywhere.
• 7. It is easier to write an incorrect program
  than understand a correct one.
• 118. If you can imagine a society in which the
  computer- robot is the only menial, you can
  imagine anything.
• 119. Programming is an unnatural act.
• 120. Adapting old programs to fit new machines
  usually means adapting new machines to behave
  like old ones.
• http//www.cs.yale.edu/homes/perlis-alan/quotes.ht
  ml

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Language evolution versus revolution

• Are new languages really new?
• First we must ask in what way is a language
  new?
• Significantly improves upon 1st generation
  languages
• E.g. better than ALGOL, LISP and Simula in some
  key ways
• Programmer productivity, program correctness,
  efficiency, reusability, extensibility,
  usderstandability, etc
• Evolutionary progress since 1960?
• Revolutionary progress since 1960?
• Any candidate? What about java?
• http//java.sun.com/people/jag/green/index.html
• http//ei.cs.vt.edu/wwwbtb/book/chap1/java_hist.h
  tml

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Language Design

• What are good design criteria for a language?
• What do the experts say?
• Fundamental Concepts in Programming Language,
  Christopher Strachey
• On the Design of Programming Languages, Nikalus
  Wirth
• Hints on Programming Language Design, C.A.R.
  Hoare
• Why Pascal is Not My Favorite Language, Brian
  Kernighan
• Lisp notes on its past and Future, John
  McCarthy
• Growing a Language, Guy Steele

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Language Designers

• Christopher Strachey
• Founded Oxford universitys Programming Research
  Group (PRG) in early 1960s
• Co-invented Scott-Strachey denotational
  semantics, with Dana Scott
• Sir C.A.R. (Tony) Hoare, FRS
• ALGOL 68, quicksort, find, monitors, CSP,
  axiomatic semantics (Hoare Logic)
• Niklaus Wirth
• Invented Euler, Algol-W, Pascal, Pascal-P,
  Modula, Modula-2, Oberon
• 1984 Turing Award