CSC 1800 Organization of Programming Languages Introduction, - PDF document

CSC 1800 CSC 1800 Organization of Programming Languages Introduction, Welcome & Getting Started 1 Course Overview ⚫ Welcome! ⚫ Web site ⚫ Syllabus ⚫ Schedule ⚫ Slides, Reading Assignments ⚫ Video Recordings ⚫ Attendance ⚫ Blackboard – handing in, gradebook, etc. 2 2 1

CSC 1800 Assessment 50% Assignments (questions, tasks, programming) 15% Exam #1 (midterm) 10% Programming language presentation 15% Exam #2 (final) 10% Participation (attendance, class discussion, intellectual contribution to class) 3 3 Class Style ⚫ Lecture ⚫ Demo ⚫ Hand-on Activities ⚫ Problem solving ⚫ Language design & programming ⚫ Presentations ⚫ Blackboard – gradebook, assignments, exams ⚫ Discussion ( Blackboard or Piazza ) – questions & answers 4 4 2

CSC 1800 Goals for Week One ⚫ Names and faces ⚫ Seating chart filled out ⚫ Intro to Programming Languages ⚫ First experiments ⚫ Start homework assignment #1 5 5 INTRODUCTION TO PROGRAMMING LANGUAGES 6 6 3

CSC 1800 Why Study Programming Languages? ⚫ Increased capacity to express ideas ⚫ Improved background for choosing appropriate language ⚫ Increased ability to learn new languages ⚫ Better understanding of the significance of implementation ⚫ Better use of languages that are already known ⚫ Overall advancement of computing 7 7 Programming Domains ⚫ Scientific Applications (Fortran) ⚫ Business Applications (COBOL) ⚫ Artificial Intelligence (LISP, Prolog) ⚫ Systems Programming (C) ⚫ Web Software (HTML, PHP, Java) 8 8 4

CSC 1800 Language Evaluation Criteria ⚫ Readability : the ease with which programs can be read and understood ⚫ Writability : the ease with which a language can be used to create programs ⚫ Reliability : conformance to specifications (i.e., performs to its specifications) ⚫ Portability : moving program from one implementation to another ⚫ Generality : applicability to a wide range of domains ⚫ Well-definedness : completeness of language ⚫ Cost : easy to learn, use, maintain 9 9 Influences on Language Design ⚫ Computer Architecture Languages are developed around the prevalent computer architecture, – known as the von Neumann architecture ⚫ Programming Methodologies – New software development methodologies (e.g., object-oriented software development) led to new programming paradigms and by extension, new programming languages 10 10 5

CSC 1800 The von Neumann Architecture Memory (stor es bot h instructi ans and data) R es ult s of Instructions and data op erations - Arithme ti c and Control i- Input and output devic es logic un it unit Ce ntral pro cess ing unit 11 11 The von Neumann Architecture ⚫ Fetch-execute-cycle initialize the program counter repeat forever fetch the instruction pointed by the counter increment the counter decode the instruction execute the instruction end repeat 12 12 6

CSC 1800 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 ⚫ Since: Write-once-run-anywhere, rapid devel, long-term maintainability, focus on OOP 13 13 LANGUAGE PARADIGMS & IMPLEMENTATIONS 14 14 7

CSC 1800 Language Categories or Paradigms ⚫ Imperative – Central features are variables, assignment statements, and iteration – Include languages that support object-oriented programming Include scripting languages – Include the visual languages – Examples: C, Java, Perl, JavaScript, Visual BASIC .NET, C++ – ⚫ 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 – ⚫ Markup – Markup languages extended to support some programming – Examples: HTML, LaTex, XML 15 15 Implementation Methods ⚫ Compilation – Programs are translated into machine language ⚫ Interpretation – Programs are interpreted by another program known as an interpreter ⚫ Hybrid – A compromise between compilers and interpreters 16 16 8

CSC 1800 Compilation ⚫ Translate high-level program (source language) into machine code (machine language) ⚫ Slow translation, fast execution ⚫ Compilation process has several phases: – lexical analysis: converts characters in the source program into lexical units – syntax analysis: transforms lexical units into parse trees which represent the syntactic structure of program – Semantics analysis: generate intermediate code – code generation: machine code is generated 17 17 Compilation Process lexical ana l yzer LexicaluniU Syntax analyzer Intermediate code generator Op(1m1zatloo (oplional) (and~ntic ,_ ;malyzer) Intermediate M!lthine l nputdala Language Compu1.cr Resulu 18 18 9

CSC 1800 Interpretation ⚫ No translation ⚫ Easier implementation of programs (run-time errors can easily and immediately be displayed) ⚫ Slower execution (10 to 100 times slower than compiled programs) ⚫ Often requires more space ⚫ Now rare for traditional high-level languages ⚫ Significant comeback with some Web scripting languages (e.g., JavaScript, PHP) 19 19 Interpretation Process Source program /Input data Interpreter Results 20 20 10

CSC 1800 PARADIGM EXAMPLES 21 21 How Many Languages? ⚫ There are over 700 programming languages that were developed and used enough to be recognized ⚫ How many languages should you know? ⚫ Good to know: HTML, CSS, JavaScript, Java, C, C++, C#, Python, PHP, Perl, Swift, – Go, R, TypeScript, Shell, PowerShell, Batch, SQL, MATLAB, Ruby, Groovy, Scala, Haskell, Fortran, COBOL 22 22 11

CSC 1800 Factorial ⚫ A factorial of N! an integer N is the product of all integers from 1 to N n! = n x (n - 1) x (n - 2) x (n - 3) x · · · x 3 x 2 x 1 ⚫ For example: 5! = 5 X 4 X 3 X 2 X 1 = 120 23 23 Imperative Languages - C ⚫ Example: a factorial function in C int fact(int n) { int sofar = 1; while (n>0) sofar *= n--; return sofar; } ⚫ Hallmarks of imperative languages: Assignment – Iteration – – Order of execution is critical – Fast, maps easily to hardware instructions 24 24 12

CSC 1800 Functional Languages - ML ⚫ Example: a factorial function in ML fun fact x = if x <= 0 then 1 else x * fact(x-1); ⚫ Hallmarks of functional languages: – Single-valued variables – Heavy use of recursion 25 25 Functional Languages - Lisp ⚫ Example: a factorial function in Lisp (defun fact (x) (if (<= x 0) 1 (* x (fact (- x 1))))) ⚫ Looks very different from ML ⚫ But ML and Lisp are closely related Single-valued variables: no assignment – Heavy use of recursion: no iteration – 26 26 13

CSC 1800 Logic Languages - Prolog ⚫ Example: a factorial function in Prolog fact(X,1) :- X =:= 1. fact(X,Fact) :- X > 1, NewX is X - 1, fact(NewX,NF), Fact is X * NF. ⚫ Hallmark of logic languages Program expressed as rules in formal logic – Also known as "Declarative" languages – 27 27 Object Oriented Languages - Java ⚫ Objects are when you attach the code as close as you can to the data it manipulates ⚫ Paradigm can be considered imperative but data- centered. ⚫ Simple Example: a Java definition for a kind of object that can store an integer and compute its factorial 28 28 14

CSC 1800 Object Oriented Languages - Java public class Factorial { public Factorial() { } public int fact(int n) { int sofar = 1; while (n > 1) sofar *= n--; return sofar; } public static void main(String[] args) { int f = (new Factorial()).fact(5); System.out.println("result: " + f); } } 29 29 Which paradigm? - Forth ⚫ Example: a factorial function in Forth : FACTORIAL 1 SWAP BEGIN ?DUP WHILE TUCK * SWAP 1- REPEAT ; ⚫ A stack-oriented language Postscript is similar – Could be called imperative, but has little in common – with most imperative languages 30 30 15

CSC 1800 Which paradigm? - APL ⚫ Example: a factorial function in APL    X ⚫ An APL expression that computes X’s factorial Expands X it into a vector of the integers 1..X, then multiplies – them all together (You would not really do it that way in APL, since there is a – predefined factorial operator: !X) – Could be called functional, but has little in common with most functional languages 31 31 DEFINING LANGUAGES 32 32 16

CSC 1800 Language Partisans ⚫ Be aware… ⚫ There is a lot of argument about the relative merits of different languages ⚫ Every language has partisans, who praise it in extreme terms and defend it against all detractors ⚫ All languages (programming and otherwise) EVOLVE! 33 33 Language Standards ⚫ The documents that define language standards are often drafted by international committees ⚫ Can be a slow, complicated and rancorous process ⚫ Not many languages preserve backward compatibility over the long-term 34 34 17