Lecture content. Course goals. Course Introduction. TDDA69 Data and Program Structure Introduction Cyrille Berger

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1 Lecture content TDDA69 Data and Program Structure Introduction Cyrille Berger Course Introduction Concepts and models of programming languages The different programming paradigms Why different paradigms? Introduction to KL 2 / 52 Course goals Course Introduction Describe aspects of evaluation and execution in different language models Explain and demonstrate how design choices affect the expressiveness and efficacy of a programming language Analyze and value programming languages based on their evaluation and compilation strategies Implement programming languages in the form of an interpreter and a compiler 4 / 52

2 Why should you care about this course? Programming languages are the key tools that define how we think about computations, and what we are able to create. It will help you understand why programming language works a certain way and what are the limits What you learn during this course will give you the power to learn, choose, and craft your tools effectively. In this course we will look at programming with a scientific eye. 5 / 52 Creative extension principle Why new language/new Existing language have limitations in expressiveness With increase in complexity of the features provided, the source code complexity increase, this can be solve with new programming concept 6 / 52 Example of creative extension principl Programming languages Without exception With exception General purposes: C, C++, Java, Python... Special purposes: Prolog, Matlab, R, Agent0... Scripting: JavaScript, VBA... Historical: Fortran, Lisp... 7 / 52 8 / 52

3 Evolution of programming languages How is a program interpreted? Source code Parser Parser Abstract Syntax Tree Tree visitor Generator Source code... Bytecode Virtual Machine Assembler Assembly Operating System CPU 9 / / 52 Facebook's work on the PHP intepreter Facebook started with PHP in 2004 Back at the time, PHP was the gold standard for website programming and prototyping But this is causing problems and for practical reasons they cannot change programming language 11 / 52 What did Facebook do? The standard PHP interpreter is using a virtual machine (Zend) They developed a tool to convert PHP to C++ Then they developed a new interpreter that do Just-In-Time (JIT) compilation, called HHVM They introduced Hack, a variant of PHP with a typing system 12 / 52

4 And other examples... Google with Java, Dalvik, ART... Python with CPython vs pypy... Qt's JavaScript, switching from AST Interpretation to JIT and to a mix of JIT and AST Interpretation... Lectures 1Introduction 2Declarative Computation Model 3Declarative Concurrency and Message Passing 4Imperative programming Model 5Virtual Machines and Bytecode 6Object-Oriented Programming Model 7Macro 8Running natively JIT and Garbage Collection 9Concurrency 10Relational Programming 11GUI Programming 12Summary 13 / / 52 Book(s) Concepts, Techniques, and Models of Computer Programming by Peter Van Roy and Seif Haridi Structure and Interpretation of Computer Programs in Python by Hal Abelson, Jerry Sussman, Julie Sussman and John Denero Structure and Interpretation of Computer Programs by Hal Abelson, Jerry Sussman and Julie Sussman List of labs 1Functional Programming 2Substitution model of evaluation 3Bytecode executor 4Macros 5Garbage collector 6SQpy 15 / / 52

5 Division of time 24h lectures (in 12 sessions) 40h labs (in 20 sessions) 8h tutorials (in 4 sessions) 88h homework Last year evaluation and improvments Too much overlap with other courses Course book is not interesting New lectures focused on programming models and evaluation models Switch to a different course book Transition to a new lab serie 17 / / 52 Defining a programming language Concepts and models of programming languages Syntax Defines what is valid. Defined by grammar rules Define how to make statements out of tokens Semantics Define what the program does during execution It should be simple and allows to reason about the program Text characters Lexer tokens Parser statements Interpreter 20 / 52

6 Concepts-based approach How to differentiate programming languages? Factorize programming language according to concept used Java: procedure, closure, state, SQL (SELECT): procedure, closure, search,... Adding concepts solve limitations in expressiveness (creative extension principle) but added to the learning curve and complexity of the The different programming paradigms 21 / 52 What is a programming paradigm? Programming paradigm is a method of classification of programming language according to their style and features. How to define a paradigm? How to match a language to a paradigm? 23 / / 52

7 Programming Paradigm (2/2) declarative functional Imperative Symbolic Constraint Logic Object-Oriented Declarative Expresses logic of computation without control flow: What should be computed and not how it should be computed. Examples: XML/HTML, antlr4/yacc/ regular expressions, make/ants, SQL, / / 52 Declarative - Examples <b>hello world!</b> SELECT name FROM student WHERE course eq 'TDDA69' grammar Hello; r : 'hello' ID; ID : [a-z]+ ; WS : [' '\t\r\n]+ -> skip ; 27 / 52 Functional Computation are treated as mathematical function without changing any internal state Examples: Lisp, Scheme, Haskell / 52

8 Functional - Examples (print "Hello World") (take 25 (squares-of (integers))) -> ( ) Imperative Express how computation are executed Describes computation in term of statements that change the internal state Examples: C/C++, Pascal, Java, Python, JavaScript / / 52 Imperative - Examples Object-Oriented for(var i = 1; i < 26; ++i) { var sq = i*i; console.log(sq) #include <stdio.h> int main() { char ch; printf("enter a character\n"); scanf("%c", &ch); if (ch == 'a' ch == 'A' ch == 'e' ch == 'E' ch == 'i' ch == 'I' ch =='o' ch=='o' ch == 'u' ch == 'U') printf("%c is a vowel.\n", ch); else printf("%c is not a vowel.\n", ch); return 0; Based on the concept of objects, which are data structures containing fields and methods Programs are designed by making objects interact with each others Examples: C++, Java, C#, Python, Ruby, JavaScript / / 52

9 Object-Oriented - Programming #include <iostream> class Character : public Symbol { public: Character(char _c) : m_c(_c) { bool isvowel() const { return ch == 'a' ch == 'A' ch == 'e' ch == 'E' ch == 'i' ch == 'I' ch =='o' ch=='o' ch == 'u' ch == 'U'; private: char m_c; ; int main() { char c; std::cout << "Enter a character:\n"; std::cin >> c; Character ch(c); if(ch.isvowel()) { std::cout << c << " is a vowel.\n"; else { std::cout << c << " is not a vowel.\n"; Logic and symbolic Logic Based on Formal logic: expressing facts and rules Symbolic A program can manipulate its own formulas and components as if they are data Example: prolog 33 / / 52 Logic programming likes(mary,food). likes(mary,wine). likes(john,wine). likes(john,mary).?- likes(mary,food). yes.?- likes(john,wine). yes.?- likes(john,food). 35 / 52 Symbolic programming d( X, X, 1 ):-!. /* d(x) w.r.t. X is 1 */ d( C, X, 0 ):- atomic(c). /* If C is a constant */ /* then d(c)/dx is 0 */ d( U+V, X, R ):- /* d(u+v)/dx = A+B where */ d( U, X, A ), /* A = d(u)/dx and */ d( V, X, B ), R = A + B.... d( sin(w), X, Z*cos(W) ):- /* d(sin(w))/dx = Z*cos(W) */ d( W, X, Z). /* where Z = d(w)/dx */ d( exp(w), X, Z*exp(W) ):- /* d(exp(w))/dx = Z*exp(W) */ d( W, X, Z). /* where Z = d(w)/dx */...?- d(cos(2*x+1), X, what) what = 2*sin(2*X+1) 36 / 52

10 Constraint Programming Constraint A relation between two variables are stated in the form of a constraint (can be logic or numerical) Example: Oz (functional), Kaleidoscope (imperative), Prolog (logic) 37 / 52 Constraint Programming - Examples local proc {MyScript Solution X = {FD.int 1#10 Y = {FD.int 1#10 Z = {FD.int 1#10 in Solution = unit(x:x y:y z:z) X + Y =: Z X <: Y %% search strategy {FD.distribute naive Solution end in {Browse {SearchAll MyScript end 38 / 52 Is there a paradigm to rule them all? Why different paradigms? In theory you can program everything in C/C++ and imperative programming, or functional programming... But is that convenient? And is that safe? 40 / 52

11 Functional vs Imperative Declarative vs Imperative Double all the numbers in an array var numbers = [1,2,3,4,5] Imperative: var doubled = [] for(var i = 0; i < numbers.length; i++) { var newnumber = numbers[i] * 2 doubled.push(newnumber) Functional: var doubled = numbers.map(function(n) { return n * 2 ) 41 / 52 Select all the dogs that belongs to a specific owner Declarative: SELECT * from dogs INNER JOIN owners WHERE dogs.owner_id = owners.id Imperative: var dogswithowners = [] var dog, owner for(var dog in dogs) { for(var owner in owners) { if (owner && dog.owner_id == owner.id) { dogswithowners.push({ dog: dog, owner: owner ) 42 / 52 Functional vs Imperative Imperative language (C/C++, Java...) Basic constructs are imperative statements Change existing values, states x = x + 1 y = f(x) while(x>0)... Functional language Basic constructs are declarative Declare new values function f(x) { return x + 1; Computations are primarily done by evaluating expressions Pure if all constructs are declarative Introduction to KL 43 / 52

12 Kernel Language How can we seperate and identify the fundamental concepts of a language? Approach to give a scientific basis to programming: Lambda calculus: reduce programming to a minimal number of elements Virtual machine: defines a language as an implementation Multiparadigm language Kernel language: is the minimal language that you need for a given paradigm Kernel Language The most simple language Select a computation model Define a mapping scheme of full programming language into the kernel language 45 / / 52 KL Linguistic abstractions vs syntaxic suga Practical language Kernel language Practical language Provides usefull abstractions for the programmer Can be extended with linguistic abstractions Kernel language Easy to understand and reason Has a precise (formal) semantic Linguistic abstractions, provide higher level concepts that the programmer can use to model, and reasons about programs functions, iterations, classes, streams... Syntactic sugar are short cuts to improve readability 47 / / 52

13 KL Syntax KL is (almost) a Kernel Language You will be developing its interpreter during the labs Written in RPython It is defined as: syntax: close to C/JavaScript semantic: +procedure+closure+cell In the future, based on the idea of adding concepts Mapping through a macro system (lecture 7) 49 / / 52 Modules Conclusion Course organisation Different programming paradigms KL 51 / / 52