Programming languages презентация

Programming Languages 1. Introduction Prof. O. Nierstrasz Spring Semester 2010

Programming Languages

Roadmap Course Schedule Programming Paradigms A Quick Tour of Programming Language History

Roadmap Course Schedule Programming Paradigms A Quick Tour of Programming Language History

Sources Text: Kenneth C. Louden, Programming Languages: Principles and Practice, PWS Publishing (Boston), 1993. Other Sources: Paul Hudak, “Conception, Evolution, and Application of Functional Programming Languages,” ACM Computing Surveys 21/3, 1989, pp 359-411. Clocksin and Mellish, Programming in Prolog, Springer Verlag, 1987.

Schedule Introduction Stack-based programming Scheme (guest lecture) Functional programming Types and polymorphism Lambda calculus Fixed points Programming language semantics Objects and types Logic programming Applications of logic programming Visual programming Final exam

Roadmap Course Schedule Programming Paradigms A Quick Tour of Programming Language History

What is a Programming Language? A formal language for describing computation? A “user interface” to a computer? Syntax + semantics? Compiler, or interpreter, or translator? A tool to support a programming paradigm?

What is a Programming Language? (II)

Themes Addressed in this Course

Generations of Programming Languages 1GL: machine codes 2GL: symbolic assemblers 3GL: (machine-independent) imperative languages (FORTRAN, Pascal, C ...) 4GL: domain specific application generators 5GL: AI languages … Each generation is at a higher level of abstraction

How do Programming Languages Differ? Common Constructs: basic data types (numbers, etc.); variables; expressions; statements; keywords; control constructs; procedures; comments; errors ... Uncommon Constructs: type declarations; special types (strings, arrays, matrices, ...); sequential execution; concurrency constructs; packages/modules; objects; general functions; generics; modifiable state; ...

Programming Paradigms

Compilers and Interpreters Compilers and interpreters have similar front-ends, but have different back-ends.

Roadmap Course Schedule Programming Paradigms A Quick Tour of Programming Language History

A Brief Chronology

Fortran History John Backus (1953) sought to write programs in conventional mathematical notation, and generate code comparable to good assembly programs. No language design effort (made it up as they went along) Most effort spent on code generation and optimization FORTRAN I released April 1957; working by April 1958 The current standard is FORTRAN 2003 (FORTRAN 2008 is work in progress)

Fortran … Innovations Symbolic notation for subroutines and functions Assignments to variables of complex expressions DO loops Comments Input/output formats Machine-independence Successes Easy to learn; high level Promoted by IBM; addressed large user base (scientific computing)

“Hello World” in FORTRAN All examples from the ACM "Hello World" project: www2.latech.edu/~acm/HelloWorld.shtml

ALGOL 60 History Committee of PL experts formed in 1955 to design universal, machine-independent, algorithmic language First version (ALGOL 58) never implemented; criticisms led to ALGOL 60 Innovations BNF (Backus-Naur Form) introduced to define syntax (led to syntax-directed compilers) First block-structured language; variables with local scope Structured control statements Recursive procedures Variable size arrays Successes Highly influenced design of other PLs but never displaced FORTRAN

“Hello World” in BEALGOL

COBOL History Designed by committee of US computer manufacturers Targeted business applications Intended to be readable by managers (!) Innovations Separate descriptions of environment, data, and processes Successes Adopted as de facto standard by US DOD Stable standard for 25 years Still the most widely used PL for business applications (!)

“Hello World” in COBOL

PL/1 History Designed by committee of IBM and users (early 1960s) Intended as (large) general-purpose language for broad classes of applications Innovations Support for concurrency (but not synchronization) Exception-handling on conditions Successes Achieved both run-time efficiency and flexibility (at expense of complexity) First “complete” general purpose language

“Hello World” in PL/1

Functional Languages ISWIM (If you See What I Mean) Peter Landin (1966) — paper proposal FP John Backus (1978) — Turing award lecture ML Edinburgh initially designed as meta-language for theorem proving Hindley-Milner type inference “non-pure” functional language (with assignments/side effects) Miranda, Haskell “pure” functional languages with “lazy evaluation”

“Hello World” in Functional Languages SML Haskell

Prolog History Originated at U. Marseilles (early 1970s), and compilers developed at Marseilles and Edinburgh (mid to late 1970s) Innovations Theorem proving paradigm Programs as sets of clauses: facts, rules and questions Computation by “unification” Successes Prototypical logic programming language Used in Japanese Fifth Generation Initiative

“Hello World” in Prolog

Object-Oriented Languages History Simula was developed by Nygaard and Dahl (early 1960s) in Oslo as a language for simulation programming, by adding classes and inheritance to ALGOL 60 Smalltalk was developed by Xerox PARC (early 1970s) to drive graphic workstations

Object-Oriented Languages Innovations Encapsulation of data and operations (contrast ADTs) Inheritance to share behaviour and interfaces Successes Smalltalk project pioneered OO user interfaces Large commercial impact since mid 1980s Countless new languages: C++, Objective C, Eiffel, Beta, Oberon, Self, Perl 5, Python, Java, Ada 95 ...

Interactive Languages Made possible by advent of time-sharing systems (early 1960s through mid 1970s). BASIC Developed at Dartmouth College in mid 1960s Minimal; easy to learn Incorporated basic O/S commands (NEW, LIST, DELETE, RUN, SAVE) ...

Interactive Languages ... APL Developed by Ken Iverson for concise description of numerical algorithms Large, non-standard alphabet (52 characters in addition to alphanumerics) Primitive objects are arrays (lists, tables or matrices) Operator-driven (power comes from composing array operators) No operator precedence (statements parsed right to left)

Special-Purpose Languages SNOBOL First successful string manipulation language Influenced design of text editors more than other PLs String operations: pattern-matching and substitution Arrays and associative arrays (tables) Variable-length strings ...

Symbolic Languages ... Lisp Performs computations on symbolic expressions Symbolic expressions are represented as lists Small set of constructor/selector operations to create and manipulate lists Recursive rather than iterative control No distinction between data and programs First PL to implement storage management by garbage collection Affinity with lambda calculus

4GLs “Problem-oriented” languages PLs for “non-programmers” Very High Level (VHL) languages for specific problem domains Classes of 4GLs (no clear boundaries) Report Program Generator (RPG) Application generators Query languages Decision-support languages Successes Highly popular, but generally ad hoc

“Hello World” in RPG

“Hello World” in SQL

Scripting Languages History Countless “shell languages” and “command languages” for operating systems and configurable applications

Scripting Languages ... Innovations Pipes and filters (Unix shell) Generalized embedding/command languages (TCL) Successes Unix Shell, awk, emacs, HyperTalk, AppleTalk, TCL, Python, Perl, VisualBasic ...

The future? Dynamic languages very active Domain-specific languages very active Visual languages many developments, but still immature Modeling languages emerging from UML and MDE …

What you should know! What, exactly, is a programming language? How do compilers and interpreters differ? Why was FORTRAN developed? What were the main achievements of ALGOL 60? Why do we call C a “Third Generation Language”? What is a “Fourth Generation Language”?

Can you answer these questions? Why are there so many programming languages? Why are FORTRAN and COBOL still important programming languages? Which language should you use to implement a spelling checker? A filter to translate upper-to-lower case? A theorem prover? An address database? An expert system? A game server for initiating chess games on the internet? A user interface for a network chess client?

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