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STRUCTURE OF PROGRAMMING LANGUAGES

Dr Yasser Fouad. STRUCTURE OF PROGRAMMING LANGUAGES. Book. Quote of the Day. “A language that doesn't affect the way you think about programming, is not worth knowing.” - Alan Perlis. Then you decide to get a PhD.

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STRUCTURE OF PROGRAMMING LANGUAGES

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  1. Dr Yasser Fouad STRUCTURE OF PROGRAMMING LANGUAGES

  2. Book

  3. Quote of the Day “A language that doesn't affect the way you think about programming, is not worth knowing.” - Alan Perlis

  4. Then you decide to get a PhD You get tired of the PowerPoint and its animations. You embed a domain-specific language (DSL) into Ruby. …

  5. Reasons for Studying Concepts of Programming Languages • Increased ability to express ideas • Improved background for choosing appropriate languages • Increased ability to learn new languages • Better understanding of significance of implementation • Overall advancement of computing

  6. How is this class different? It’s about: • foundations of programming langauges • but also how to design your own languages • how to implement them • and about PL tools, such as analyzers • also learn about some classical C.S. algorithms.

  7. Why a developer needs PL New languages will keep coming • Understand them, choose the right one. Write code that writes code • Be the wizard, not the typist. Develop your own language. • Are you kidding? No. Learn about compilers and interpreters. • Programmer’s main tools.

  8. Overview • how many languages does one need? • how many languages did you use? Let’s list them here:

  9. Develop your own language Are you kidding? No. Guess who developed: • PHP • Ruby • JavaScript • perl Done by smart hackers like you • in a garage • not in academic ivory tower Our goal: learn good academic lessons • so that your future languages avoid known mistakes

  10. Programming Domains • Scientific applications • Large number of floating point computations • Fortran • Business applications • Produce reports, use decimal numbers and characters • COBOL • Artificial intelligence • Symbols rather than numbers manipulated • LISP • Systems programming • Need efficiency because of continuous use • C • Web Software • Eclectic collection of languages: markup (e.g., XHTML), scripting (e.g., PHP), general-purpose (e.g., Java)

  11. Figure by Brian Hayes(who credits, in part, Éric Lévénez and Pascal Rigaux):Brian Hayes, “The Semicolon Wars.” American Scientist, July-August 2006, pp.299-303

  12. Genealogy of Common Language

  13. Programming Paradigms PS — Introduction

  14. Language Categories • Imperative • Central features are variables, assignment statements, and iteration • Examples: C, Pascal • Functional • Main means of making computations is by applying functions to given parameters • Examples: LISP, Scheme • Logic • Rule-based (rules are specified in no particular order) • Example: Prolog • Object-oriented • Data abstraction, inheritance, late binding • Examples: Java, C++ • Markup • New; not a programming per se, but used to specify the layout of information in Web documents • Examples: XHTML, XML

  15. Program • A program is a machine-compatible representation of an algorithm • If no algorithm exists for performing a task, then the task can not be performed by a machine • Programs and algorithms they represent collectively referred to as Software

  16. 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? A programming language is a notational system for describing computation in a machine-readable and human-readable form. — Louden PS — Introduction

  17. Programming Methodologies Influences • 1950s and early 1960s: Simple applications; worry about machine efficiency • Late 1960s: People efficiency became important; readability, better control structures • structured programming • top-down design and step-wise refinement • Late 1970s: Process-oriented to data-oriented • data abstraction • Middle 1980s: Object-oriented programming • Data abstraction + inheritance + polymorphism

  18. Favorite programming language June 2012 • Python (3,054) • Ruby (1,723) • JavaScript (1,415) • C (970) • C# (829) • PHP (666) • Java (551) • C++ (529) • Haskell (519) • Clojure (459) • CoffeeScript (362) • Objective C (326) • Lisp (322) • Perl (311) • Scala (233) • Scheme (190) • Other (188) • Erlang (162) • Lua (145) • SQL (101)

  19. job listings collected from Dice.com • Python 3,456 (+32.87%) • Ruby 2,141 (+39.03%) • HTML5 (+276.85%) • Flash 1,261 (+95.2%) • Silverlight 865 (-11.91%) • COBOL 656 (-10.75%) • Assembler 209 (-1.42%) • PowerBuilder (-18.71%) • FORTRAN 45 (-33.82%) • Java 17,599 (+8.96%) • XML 10,780 (+11.70%) • JavaScript (+11.64%) • HTML 9,587 (-1.53%) • C# 9,293 (+17.04%) • C++ 6,439 (+7.55%) • AJAX 5,142 (+15.81%) • Perl 5,107 (+3.21%) • PHP 3,717 (+23%)

  20. Languages in Common Use

  21. A Brief Chronology PS — Introduction

  22. ENIAC (1946, University of Philadelphia) ENIAC program for external ballistic equations:

  23. Programming the ENIAC

  24. ENIAC (1946, University of Philadelphia) programming done by • rewiring the interconnections • to set up desired formulas, etc Problem (what’s the tedious part?) • programming = rewiring • slow, error-prone solution: • store the program in memory! • birth of von Neuman paradigm

  25. Assembly – the language (UNIVAC 1, 1950) Idea: mnemonic (assembly) code • Then translate it to machine code by hand (no compiler yet) • write programs with mnemonic codes (add, sub), with symbolic labels, • then assign addresses by hand Example of symbolic assembler clear-and-add a add b store c translate it by hand to something like this (understood by CPU) B100 A200 C300

  26. Assembly Language ADDI R4 R2 21 ADDI R4,R2,21 10101100100000100000000000010101 • Use symbols instead of binary digits to describe fields of instructions. • Every aspect of machine visible in program: • One statement per machine instruction. • Register allocation, call stack, etc. must be managed explicitly. • No structure: everything looks the same.

  27. Assembler – the compiler (Manchester, 1952) • a loop example, in MIPS, a modern-day assembly code: loop: addi $t3, $t0, -8 addi $t4, $t0, -4 lw $t1, theArray($t3) # Gets the last lw $t2, theArray($t4) # two elements add $t5, $t1, $t2 # Adds them together... sw $t5, theArray($t0) # ...and stores the result addi $t0, $t0, 4 # Moves to next "element“ # of theArray blt $t0, 160, loop # If not past the end of # theArray, repeat jr $ra

  28. High-level Language • Provides notation to describe problem solving strategies rather than organize data and instructions at machine-level. • Improves programmer productivity by supporting features to abstract/reuse code, and to improve reliability/robustness of programs. • Requires a compiler.

  29. FORTRAN I (1954-57) Langauge, and the first compiler • Produced code almost as good as hand-written • Huge impact on computer science • Modern compilers preserve its outlines By 1958, >50% of all software is in FORTRAN

  30. FORTRAN I Example: nested loops in FORTRAN • a big improvement over assembler, • but annoying artifacts of assembly remain: • labels and rather explicit jumps (CONTINUE) • lexical columns: the statement must start in column 7 • The MIPS loop from previous slide, in FORTRAN: DO 10 I = 2, 40 A[I] = A[I-1] + A[I-2] 10 CONTINUE

  31. “Hello World” in FORTRAN All examples from the ACM "Hello World" project: www2.latech.edu/~acm/HelloWorld.shtml PROGRAM HELLO DO 10, I=1,10 PRINT *,'Hello World' 10 CONTINUE STOP END PS — Introduction

  32. Side note: designing a good language is hard Good language protects against bugs, but lessons take a while. An example that caused a failure of a NASA planetary probe: buggy line: DO 15 I = 1.100 what was intended (a dot had replaced the comma): DO 15 I = 1,100 because Fortran ignores spaces, compiler read this as: DO15I = 1.100 which is an assignment into a variable DO15I, not a loop. This mistake is harder to make (if at all possible) with the modern lexical rules (white space not ignored) and loop syntax for (i=1; i < 100; i++) { … }

  33. “Hello World” in COBOL 000100 IDENTIFICATION DIVISION. 000200 PROGRAM-ID. HELLOWORLD. 000300 DATE-WRITTEN. 02/05/96 21:04. 000400* AUTHOR BRIAN COLLINS 000500 ENVIRONMENT DIVISION. 000600 CONFIGURATION SECTION. 000700 SOURCE-COMPUTER. RM-COBOL. 000800 OBJECT-COMPUTER. RM-COBOL. 001000 DATA DIVISION. 001100 FILE SECTION. 100000 PROCEDURE DIVISION. 100200 MAIN-LOGIC SECTION. 100300 BEGIN. 100400 DISPLAY " " LINE 1 POSITION 1 ERASE EOS. 100500 DISPLAY "HELLO, WORLD." LINE 15 POSITION 10. 100600 STOP RUN. 100700 MAIN-LOGIC-EXIT. 100800 EXIT. PS — Introduction

  34. 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 PS — Introduction

  35. “Hello World” in BEALGOL BEGIN FILE F (KIND=REMOTE); EBCDIC ARRAY E [0:11]; REPLACE E BY "HELLO WORLD!"; WHILE TRUE DO BEGIN WRITE (F, *, E); END; END. PS — Introduction

  36. “Hello World” in PL/1 HELLO: PROCEDURE OPTIONS (MAIN); /* A PROGRAM TO OUTPUT HELLO WORLD */ FLAG = 0; LOOP: DO WHILE (FLAG = 0); PUT SKIP DATA('HELLO WORLD!'); END LOOP; END HELLO; PS — Introduction

  37. “Hello World” in Functional Languages SML Haskell print("hello world!\n"); hello() = print "Hello World" PS — Introduction

  38. Goto considered harmful L1: statement if expression goto L1 statement Dijkstra says: gotos are harmful • use structured programming • lose some performance, gain a lot of readability how do you rewrite the above code into structured form?

  39. 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 ... OUTPUT = 'Hello World!' END PS — Introduction

  40. 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 Begin while 1 = 1 do begin outtext ("Hello World!"); outimage; end; End; Transcript show:'Hello World';cr PS — Introduction

  41. 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 PS — Introduction

  42. “Hello World” in SQL CREATE TABLE HELLO (HELLO CHAR(12)) UPDATE HELLO SET HELLO = 'HELLO WORLD!' SELECT * FROM HELLO PS — Introduction

  43. Scripting Languages History Countless “shell languages” and “command languages” for operating systems and configurable applications • Unix shell (ca. 1971) developed as user shell and scripting tool • HyperTalk (1987) was developed at Apple to script HyperCard stacks • TCL (1990) developed as embedding language and scripting language for X windows applications (via Tk) • Perl (~1990) became de facto web scripting language echo "Hello, World!" on OpenStack show message box put "Hello World!" into message box end OpenStack puts "Hello World " print "Hello, World!\n"; PS — Introduction

  44. 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; ... PS — Introduction

  45. Improved background for choosing appropriate languages • C vs. Modula-3 vs. C++ for systems programming • Fortran vs. APL vs. Ada for numerical computations • Ada vs. Modula-2 for embedded systems • Common Lisp vs. Scheme vs. Haskell for symbolic data manipulation • Java vs. C/CORBA for networked PC programs

  46. Evolution of Programming Languages • ALGOL - 60 (ALGOrithmic Language) Goals : Communicating Algorithms Features : Block Structure (Top-down design) Recursion (Problem-solving strategy) BNF - Specification • LISP (LISt Processing) Goals : Manipulating symbolic information Features : List Primitives Interpreters / Environment

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