Challenge the future

DelftUniversity ofTechnology

TI1220Concepts of Programming Languages

Eelco Visser

Concepts of Programming Languages

today’s lecture

TI1220 - Introduction

Overview

A new course

• from IN1605-B to TI1220

What is this course about?

• why study concepts of programming languages?

How is this course organized?

• lectures and assignments

Introduction to Scala

• writing and running Scala programs

2

TI 1220 - Lecture 1: Introduction

A New Course

I

3

the only constant is change

TI1220 - Introduction

A New Course

IN1605-B: Algoritmen en Programmeertalen: Programmeertalen

• 4 ECTS

• Haskell + C

• Peter Kluijt

TI1220: Concepten van Programmeertalen

• 6 ECTS

• Scala + C + JavaScript

• Eelco Visser

4

Eelco Visser

TI1220 - Introduction

Under New Management

Lecturer

• Dr. Eelco Visser

• UHD in Software Engineering Research Group

• http://eelcovisser.org

• Contact: e.visser@tudelft.nl

• first ask student assistants

• send questions by email

• appointment if necessary

5

software language design & engineering

TI1220 - Introduction

My Research

6

Spoofax Language Workbench

• design and implement languages & IDEs

• from high-level declarative specification

Domain-specific language design

• WebDSL: a DSL for web programming

• Mobl: a DSL for mobile web applications

Interaction design

• researchr.org: building a digital library

TI1220 - Introduction

Examination Old Course

You can still sit for exams of IN1605-B

• Provided you have finished the lab (practicum)

Sittings

• Together with exam for this course (TI1220)

• April 11, 2010

• June 22, 2010

7

TI1220 - Introduction

Feedback Appreciated

An invitation to Murphy

• New content

• New software

• New lectures, assignments, exams

• New lecturer

• New assistants (mostly)

Please let us know how it goes

• report problems early

• also let us know what goes right :)

8

TI 1220 - Lecture 1: Introduction

Concepts of Programming Languages

II

9

TI1220 - Introduction

Computers Process Data

10

computerdata data

TI1220 - Introduction

Programmable Computers

11

computerdata data

program

TI1220 - Introduction

Programming Language

12

computerdata data

L program

computability

TI1220 - Introduction

Turing Machines

Turing/Church Thesis

• Every effective computation can be carried out by a Turing machine*

Corollary

• All (Turing Complete) programming languages can express all effective computations

• Why bother with new programming languages?

(*) see IN2505

13

timeline

TI1220 - Introduction 14

1986 1990 1990 1991 1991 1993 1994 1995 1996 1996 1997 1997 2000 2001 2001 2003 2003 2004

History of Programming Languages

©2004 O’Reilly Media, Inc. O’Reilly logo is a registered trademark of O’Reilly Media, Inc. All other trademarks are property of their respective owners. part#30417

19601954 1965 1970 1975 1980 1985 1990 1995 2000 20022001 2003 2004

For more than half of the fifty years computer programmers have beenwriting code, O’Reilly has provided developers with comprehensive,in-depth technical information. We’ve kept pace with rapidly changingtechnologies as new languages have emerged, developed, andmatured. Whether you want to learn something new or needanswers to tough technical questions, you’ll find what you need in O’Reilly books and on the O’Reilly Network.

This timeline includes fifty of the more than 2500 documented programming languages. It is based on an original diagram createdby Éric Lévénez (www.levenez.com), augmented with suggestionsfrom O’Reilly authors, friends, and conference attendees.

For information and discussion on this poster, go to www.oreilly.com/go/languageposter.

www.oreilly.com

This timeline includes 50 of the more than 2500 documented programming languages.

History of Programming Languages

TI1220 - Introduction

Programming Languages in TI

15

TI1200: Object-Oriented Programming

• Java

TI1400: Computer Systems

• Assembly

TI1500: Web- and Database Technology

• HTML, PHP, SQL, JavaScript

TI1600: Multi-Agent Systems

• Prolog, GOAL

TI1220 - Introduction 16

“A programming language is low level when its programs require attention to the irrelevant”

Alan J. Perlis. Epigrams on Programming. SIGPLAN Notices, 17(9):7-13, 1982.

purpose of programming languages

TI1220 - Introduction

Understanding Computation

17

Encoding computation

• Computer needs list of instructions to move its parts

Understanding computation

• Discuss concepts

• Formulate algorithms

• Reason about problem solutions

Programming languages are for people

concepts of programming languages

TI1220 - Introduction

Increasing the Level of Abstraction

18

f(e1)

calc: push eBP ; save old frame pointer mov eBP,eSP ; get new frame pointer sub eSP,localsize ; reserve place for locals . . ; perform calculations, leave result in AX . mov eSP,eBP ; free space for locals pop eBP ; restore old frame pointer ret paramsize ; free parameter space and return

push eAX ; pass some register resultpush byte[eBP+20] ; pass some memory variable (FASM/TASM syntax)push 3 ; pass some constantcall calc ; the returned result is now in eAX

def f(x)={ ... }

http://en.wikipedia.org/wiki/Calling_convention

concepts of programming languages

TI1220 - Introduction

Programming Models

Language provides model of computation

• data & operations, composition & abstraction

Language targets application domain

• Systems programming

• Embedded systems

• Web programming

• Enterprise software

19

concepts of programming languages

TI1220 - Introduction

Programming Language DNA

Scope and binding

• declaration and binding of names, free and bound occurrences, renaming, substitution

Data structures

• product and sum types, records, recursive types

Modularization and data abstraction

• modules, classes, higher-order functions, class-based vs prototype inheritance

Syntax and interpretation

20

concepts of programming languages

TI1220 - Introduction

Why Study Concepts?

Design abstractions for new domains

• from library to language feature

• apply PL techniques (MapReduce)

Learn new computational models

• understand fundamental ideas underlying PLs

• experience with variety of models

• learn new languages in future

Choosing the right language

21

concepts of programming languages

TI1220 - Introduction

Goals of this Course

• Understand programming languages and programs in terms of concepts that transcend individual languages

• Consider advantages and disadvantages in the use of particular languages and concepts

• Analyze programs in terms of concepts

• Application of concepts in designing programs

22

concepts of programming languages

TI1220 - Introduction

Approach

Study three concrete languages

• Scala + C + JavaScript

• Learn to program in these languages

• Learn concepts by using them in programming

• Programming assignments about languages

Generalize

• What are the underlying ideas?

• Learn to learn new languages

23

functional programming

TI1220 - Introduction

Scala

• Lecture 1: Getting Started with Scala

• Lecture 2: Functional Objects

• Lecture 3: Functions & Closures

• Lecture 4: List Programming (Recursion)

• Lecture 5: Trees & XML

• Lecture 6: Composition, Inheritance, Traits

• Lecture 7: Modular Programming

• Assignment: interpreter for tiny functional language

24

systems programming

TI1220 - Introduction

C

• Lecture 8: Memory Management

• stack vs heap

• pointers

• Lecture 9: Implementing Objects

• function pointers

• simulating dynamic dispatch

• Assignment: implementing OO in C

25

web programming

TI1220 - Introduction

JavaScript

Prototype-Based Object-Oriented Language

• Lecture 10: Prototypal Inheritance

• History: Smalltalk, Self (Squeak)

• Lecture 11: Asynchronous functions

• Lecture 12: DOM manipulation

• Lecture 13: Regular expressions

• Lecture 14: mobl: a domain-specific language for the mobile web

• Assignment: playing with prototypes

26

implementation of programming languages

TI1220 - Introduction 27

Meta-Programming

Other courses consider internals of languages

• IN2505: Fundamental Computer Science 2: Theory of Computation

• grammars and automata

• IN4303: Compiler Construction

• translation of high-level source to machine language

• IN4308: Model-Driven Software Development

• design of domain-specific software languages

TI 1220 - Lecture 1: Introduction

Course Organization

III

28

course organization

TI1220 - Introduction

Ingredients

This is a semester course

• Q3 + Q4

Lectures

• Tuesday morning

Practicum

• on Tuesday or Thursday afternoon

• Exercises + Graded Assignments

Exams

29

course organization

TI1220 - Introduction

Exams

Exam 1

• Monday 11 April, 2011, 9:00-12:00

• E1: about material of Q3 (Scala)

Exam 2

• Wednesday, 22 June, 2011, 9:00-12:00

• If Exam 1 >= 6

• then E2a: material of Q4 (C+JavaScript)

• else E2b: material Q3+Q4 (Scala+C+JavaScript)

30

course organization

TI1220 - Introduction

Exams

Exam 3 (resit)

• If Exam 2 < 6, even if Exam 1 >= 6

• Wednesday, 24 August, 2011, 9:00-12:00

• E3: material Q3+Q4 (Scala+C+JavaScript)

Note

• next year programming exams

31

course organization

TI1220 - Introduction

Practicum

Scala (Q3)

• Exercises: hand in on paper to assistants at end of lab!

• Assignment 1 (graded)

C (Q4)

• Assignment 2 (graded)

JavaScript (Q4)

• Assignment 3 (graded)

Graded assignments should be submitted as code

32

course organization

TI1220 - Introduction

Final Grade

33

val H = all exercises handed in

val A = 0.4*A1 + 0.3*A2 + 0.3*A3

val E2 = if(E1 >= 6) (E1 + E2a)/2

else E2b

val E = if(E2 >= 6) E2 else E3

val G = if(H && Ai >= 6 && E >= 6)

0.4*A + 0.6E

else min(E, 5)

course organization

TI1220 - Introduction

Practicum Groups

34

Tuesday: Group 1

• mentor groups 1 to 6

Thursday: Group 2

• mentor groups 7 to 12

course organization

TI1220 - Introduction

Practicum Assistants

35

Tuesday Thursday

Maartje de Jonge Sander van der Burg

Laurent Verweijen Bart van Vuuren

Vlad Vergu Peter Pul

Joost Heijkoop

TI1220 - Introduction 36

coffee break

Term Rewriting

The Scala Programming Language

IV

37

imperative vs functional programming

TI1220 - Introduction

Programming Language Schools

Imperative Programming (Algol, C, Pascal)

• programming with side effects

• structured control-flow

Object-Oriented Programming (C++, Java)

• imperative programming with data abstraction

Functional Programming (ML, Haskell)

• functions as first-class citizens

• immutable data (pure)

38

history

TI1220 - Introduction 39

Pizza

POPL 1997

• "Pizza into Java: Translating theory into practice", Martin Odersky and Philip Wadler. Proc. 24th ACM Symposium on Principles of Programming Languages, Paris, France, January 1997.

Extending Java with Functional Concepts

• Parametric polymorphism (generics)

• First-class functions (function pointers)

• Algebraic data types (class cases and pattern matching)

Continued in GJ and Java Generics

Philip Wadler, Martin Odersky, Gilad Bracha, Dave Stoutamire (source: http://lamp.epfl.ch/pizza/gj/)

history

TI1220 - Introduction 40

Scala

A Scalable Language

• object-oriented + functional programming

Properties

• compatible (combines with Java)

• concise (sugar + abstractions)

• high-level

• statically typed

Designed by Martin Odersky et al. at EPFL

history

TI1220 - Introduction

Scala in Industry

Scala at Twitter

• Ruby-on-Rails did not scale

• Replaced back-end processing (API) with Scala

BankSimple

• Back-end services in Scala or Clojure

Alex Payne

• Programming Scala by Wampler & Payne

41

Book

TI1220 - Introduction

Programming in Scala

42

Programming in ScalaA comprehensive step-by-step guide

by Martin Odersky, Lex Spoon, and Bill Venners

http://www.artima.com/shop/programming_in_scala

Available as e-book (PDF)

Lectures are based on book; not everything in book is on slides; reading book is required; see Literature slides at end of each lecture for required reading!

B:2.1 TI1220 - Introduction

Installing Scala

Download Interpreter & Compiler

• Make your own installation (assignment 1)

• http://www.scala-lang.org/downloads

Editors

• Emacs, Vi, <your favorite editor>

Integrated Development Environments

• Plugins for Eclipse, IntelliJ, NetBeans

43

B:2.1

$ scalaWelcome to Scala version 2.8.0.final (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_22).Type in expressions to have them evaluated.Type :help for more information..

TI1220 - Introduction

The Scala Interpreter

44

B:2 Term Rewriting

Variables and Functions

V

45

B:2.1

scala> 1 + 2res0: Int = 3

scala> res0 * 3res1: Int = 9

scala> println("Hello, world!")Hello, world!

repl: read, eval, print loop

TI1220 - Introduction

Evaluating Expressions

46

B:2.2

scala> val msg = "Hello, world!"msg: java.lang.String = Hello, world!

scala> val msg2: java.lang.String = | "Hello again, world!"msg2: java.lang.String = Hello again, world!

scala> val msg3: String = "Hello yet again, world!"msg3: String = Hello yet again, world!

scala> println(msg)Hello, world!

binding values to names

TI1220 - Introduction

Variable Declaration and Use

47

B:2.3

scala> msg = "Goodbye cruel world!"<console>:6: error: reassignment to val msg = "Goodbye cruel world!"

scala> var greeting = "Hello, world!"greeting: java.lang.String = Hello, world!

scala> greeting = "Leave me alone, world!"greeting: java.lang.String = Leave me alone, world!

changing value bound to name

TI1220 - Introduction

Immutable and Mutable Variables

48

B:2.3

scala> def max(x: Int, y: Int): Int = { if (x > y) x else y }max: (x: Int,y: Int)Int

scala> max(3, 5)res2: Int = 5

binding functions to names

TI1220 - Introduction

Function Definition and Call

49

scala> def max2(x: Int, y: Int) = if (x > y) x else y max: (x: Int,y: Int)Int

B:2.3

scala> def greet() = println("Hello, world!")greet: ()Unit

scala> greet()Hello, world!

the type of side effects

TI1220 - Introduction

Unit

50

B:2.4

$ scala hello.scala Hello, world, from a script!

TI1220 - Introduction

Scala Scripts

51

//file: hello.scalaprintln("Hello, world, from a script!")

B:2.4

$ scala helloarg.scala delftHello, delft!

with arguments

TI1220 - Introduction

Scala Scripts

52

//file: helloarg.scala// Say hello to the first argumentprintln("Hello, "+ args(0) +"!")

B:2.5

// file: printargs.scalavar i = 0while (i < args.length) { if (i != 0) print(" ") print(args(i)) i += 1}println()

imperative style

TI1220 - Introduction

Control-Flow

53

$ scala printargs.scala imperative styleimperative style

B:2.5

// file: printargsfun.scalaargs.foreach(arg => println(arg))

functional style

TI1220 - Introduction

Control-Flow

54

$ scala printargsfun.scala first class functionsfirstclassfunctions

B:2.5

for (arg <- args) println(arg)

functional style

TI1220 - Introduction

Control-Flow

55

B:3.11 TI1220 - Introduction

Functional Style

56

Functional style

• functions are values

• operations map input values to output values

• instead of changing values in place (side effects)

A balanced attitude

• Prefer vals, immutable objects, and methods without side effects.

• Use vars, mutable objects, and methods with side effects when you have a specific need and justification for them.

B:3.12

$ scala linecounts.scala linecounts.scala 22 | import scala.io.Source 0 | 55 | def widthOfLength(s: String) = s.length.toString.length 0 | 22 | if (args.length > 0) {54 | val lines = Source.fromFile(args(0)).getLines.toList37 | val longestLine = lines.reduceLeft(49 | (a, b) => if (a.length > b.length) a else b 3 | )43 | val maxWidth = widthOfLength(longestLine)23 | for (line <- lines) {50 | val numSpaces = maxWidth - widthOfLength(line)33 | val padding = " " * numSpaces47 | println(padding + line.length +" | "+ line) 3 | } 1 | } 4 | else46 | Console.err.println("Please enter filename")

TI1220 - Introduction 57

B:2.3

import scala.io.Sourceif (args.length > 0) { for (line <- Source.fromFile(args(0)).getLines) println(line.length + " | " + line)} else Console.err.println("Please enter filename")

charcounts

TI1220 - Introduction 58

$ scala countchars1.scala countchars1.scala 22 | import scala.io.Source22 | if (args.length > 0) {49 | for (line <- Source.fromFile(args(0)).getLines)37 | println(line.length + " " + line)6 | } else46 | Console.err.println("Please enter filename")

Print Lines

B:3.12

def widthOfLength(s: String) = s.length.toString.length

val lines = Source.fromFile(args(0)).getLines.toList

val longestLine = lines.reduceLeft( (a, b) => if (a.length > b.length) a else b)

val maxWidth = widthOfLength(longestLine)

charcounts

TI1220 - Introduction 59

Width of Longest Line

B:3.12

for (line <- lines) { val numSpaces = maxWidth - widthOfLength(line)

val padding = " " * numSpaces

println(padding + line.length +" | "+ line)}

charcounts

TI1220 - Introduction 60

Print Lines with Length

B:3.12

import scala.io.Source

def widthOfLength(s: String) = s.length.toString.length

if (args.length > 0) { val lines = Source.fromFile(args(0)).getLines.toList val longestLine = lines.reduceLeft( (a, b) => if (a.length > b.length) a else b ) val maxWidth = widthOfLength(longestLine) for (line <- lines) { val numSpaces = maxWidth - widthOfLength(line) val padding = " " * numSpaces println(padding + line.length +" | "+ line) }}else Console.err.println("Please enter filename")

TI1220 - Introduction 61

B:2.3 Term Rewriting

Classes and Objects

VI

62

B:4.1

class ChecksumAccumulator {}

val acc = new ChecksumAccumulatorval csa = new ChecksumAccumulator

declaration and instantiation

TI1220 - Introduction

Class: Object Blueprint

63

B:4.1

class ChecksumAccumulator { var sum = 0}

val acc = new ChecksumAccumulatorval csa = new ChecksumAccumulator

acc.sum = 3

object state

TI1220 - Introduction

Fields (Instance Variables)

64

B:4.1

class ChecksumAccumulator { var sum = 0}

val acc = new ChecksumAccumulatorval csa = new ChecksumAccumulator

acc.sum = 3

// Won’t compile, because acc is a valacc = new ChecksumAccumulator

object state

TI1220 - Introduction

Reference vs Content

65

B:4.1

class ChecksumAccumulator { private var sum = 0}

val acc = new ChecksumAccumulatoracc.sum = 5 // Won’t compile, because sum is private

object state

TI1220 - Introduction

Data Hiding

66

B:4.1

class ChecksumAccumulator { private var sum = 0 def add(b: Byte): Unit = { sum += b } def checksum(): Int = { return ~(sum & 0xFF) + 1 }}

object behavior

TI1220 - Introduction

Methods

67

B:4.1

def add(b: Byte): Unit = { b = 1 // This won’t compile, because b is a val sum += b}

parameters are vals

TI1220 - Introduction

Methods

68

B:4.1

// file: ChecksumAccumulator.scalaclass ChecksumAccumulator { private var sum = 0 def add(b: Byte) { sum += b } def checksum(): Int = ~(sum & 0xFF) + 1}

sugar

TI1220 - Introduction

Methods

69

B:4.3

import scala.collection.mutable.Mapobject ChecksumAccumulator { private val cache = Map[String, Int]() def calculate(s: String): Int = if (cache.contains(s)) cache(s) else { val acc = new ChecksumAccumulator for (c <- s) acc.add(c.toByte) val cs = acc.checksum() cache += (s -> cs) cs }}

defining ‘static’ methods

TI1220 - Introduction

Singleton Objects

70

B:4.3

ChecksumAccumulator.calculate("Every value is an object.")

methods and state

TI1220 - Introduction

Using Singleton Objects

71

B:4.4

// file: Summer.scalaimport ChecksumAccumulator.calculateobject Summer { def main(args: Array[String]) { for (arg <- args) println(arg + ": " + calculate(arg)) }}

TI1220 - Introduction

Scala Application

72

$ scalac ChecksumAccumulator.scala Summer.scala$ scala Summer of loveof: -213love: -182

Term Rewriting

Summary

VII

73

B:2.3

lessons learned

TI1220 - Introduction

Summary

Programming languages are for people

• to reason about solutions for problems

Declaration and use

• binding values to names, referring to values using names

Immutable values

• cannot be changed once created (no side effects)

Objects

• data structures with methods

74

B:2.3 TI1220 - Introduction

Exam Question

75

What happens when we execute the following code:

val greetStrings = new Array[String](3)greetStrings(0) = "Hello"greetStrings(1) = ", "greetStrings(2) = "world!\n"

(a) Error: greetStrings is an immutable variable that cannot be assigned to

(b) Error: Array is a immutable data structure that cannot be assigned to

(c) No error: greetStrings is a mutable variable that can be assigned to

(d) No error: Array is a mutable data structure that can be assigned to

B:2.3

getting started with Scala

TI1220 - Introduction 76

Exercises Week 1

Set up your Scala environment

• download and install Scala interpreter and compiler

Scala basics

• evaluating expressions

• defining functions

• running scripts

• making applications

• hand in on paper to student assistants!

required reading

TI1220 - Introduction

Literature

Programming in Scala

• Chapter 1: A Scalable Language

• Chapter 2: First Steps in Scala

• Chapter 3: Next Steps in Scala

• Chapter 4: Classes and Objects

• Chapter 5: Basic Types and Operations

77

http://researchr.org/bibliography/ti1220

TI1220 - Introduction

Literature

78

B:2.3

coming next

TI1220 - Introduction

Outlook

Functional programming

• Lecture 2: Functional Objects

• Chapters 6, 7

• Lecture 3: Functions & Closures

• Chapters 8, 9

• Lecture 4: List Programming

• Chapters 15, 16, 17

Lab Week 1

• Getting started with Scala

79

Term Rewriting

Notes

IX

80

B:2.3

copyrights

TI1220 - Introduction

Pictures

Slide 1: Kinetica by Paul Downey, Some rights reservedSlide 2: McPhillips’ Map of the City of Winnipeg by Manitoba Historical Maps, some rights reservedSlide 4: The Blue Hour by Andreas Wonisch, Some rights reservedSlide 5: by Eelco Visser, Some rights reservedSlide 8: I’m listening by Melvin Gaal, some rights reservedSlide 10: Bombe detail by Garret Coakley, Some rights reservedSlide 13: Alan Turing by oalfonso, some rights reservedSlide 14: History of Programming Languages by O’Reilly Slide: ABZ-DNA by dulhunk, some rights reservedSlide 32, 34: Envelopes by benchilada, some rights reservedSlide 33: Report card by Carosaurus, some rights reservedSlide 36: paper coffee cup by Shutterstock, some rights reserved

81

B:2.3

copyrights

TI1220 - Introduction

Pictures

Slide 40: Dinner at Roussillon (Martin Odersky) by Miles Sabin, some rights reservedSlide 41: Portrait: Alex Payne by Dave Fayram, some rights reservedSlide 43: “Plumbing Nightmare” by Natalie Wilkie, some rights reservedSlide 72: HIV: The Moleskine Summary by Niels OlsonSlide 75, 76: remember to thank all the books you haven’t read over the past three years by Natalia Osiatynska, Some rights reservedSlide 7, 73: Stupid Exam by Remi Carreiro, Some rights reservedSlide 74: Practice makes perfect by Simon ProbertSlide 10: Bombe detail by Garret Coakley, Some rights reservedSlide 29: 1.12.2011 <recipes> 362/365 by Phil Roeder, Some rights reserved

Slide 22,23: China Tibet Himalaya by Bernhard Goldbach, Some rights reservedSlide 17: Thinking at Hell’s gate by innoxiuss, Some rights reserved

82