Lecture 1: Introduction. 23. August, 2010

Transcription

1 Lecture 1: Introduction 23. August, 2010

2 Lecture Outline TDT4165 Administratrivia Programming Languages Introduction Illustration Hello World Programs Further Comments Summary

3 TDT4165 Administratrivia Course Staff Lecturer: Hans Christian Falkenberg, Teaching assistants: Børge Rødsjø, Dag Øyvind Tornes,

4 TDT4165 Administratrivia contd Sources of information Course website Mailing lists subscribe to receive official announcements subscribe to post and receive public discussion subscribe to post questions about exercises subscribe to post questions and complaints anonymously

5 TDT4165 Administratrivia contd Where to ask? Public discussions, help requests, etc.: tdt4165; tdt4165-studass; tdt4165-fagans Comments and complaints about exercises: tdt4165-fagans; hanscho Comments and complaints about the course: tdt4165-fagans;

6 TDT4165 Administratrivia contd Grading Mid-term exam (MTE): 30% (but you may choose to skip it) Final exam (FNE): 70% (100% if you skip MTE or the mark would be better without the MTE) Exercises: mandatory, but do not contribute to the final character; you must deliver correct solutions to at least 6 of the exercises. 1 1 Subject to minor changes.

7 TDT4165 Administratrivia contd Schedule Lectures: Mondays, , R5 Wednesdays, , H3 Some lectures may need to be moved (check plan on homepage) Office hours: On request. Labs (P15-414): Wednesday: ; Thursday

8 TDT4165 Administratrivia contd Key dates Midterm exam: October 18th (tentative date) Final exam: December 1st (fixed)

9 TDT4165 Administratrivia contd Pensum book P. van Roy, S. Haridi, Concepts, Techniques and Models of Computer Programming, 1st ed.

10 TDT4165 Administratrivia contd Syllabus Chapters 1 5: all sections Chapters 6 9: selected sections Selected lecture and exercise material Details will be published on the course s webpage, which take precedence over this information.

11 TDT4165 Administratrivia contd Optional material (read on your own) Sebesta, Concepts of Programming Languages

12 TDT4165 Administratrivia contd Optional material (read on your own) Scott, Programming Language Pragmatics

13 TDT4165 Administratrivia contd Additional material (for your interest) Friedman, Wand, Haynes, Essentials of Programming Languages

14 TDT4165 Administratrivia contd Additional material (for your interest) Cooper, Torczon, Engineering a Compiler

15 TDT4165 Administratrivia contd Additional material (for your interest) Aho, Lam, Sethi, Ullman, Compilers

16 TDT4165 Administratrivia contd Additional material (for your interest) Further optional books may be referenced where relevant. They cover: various aspects of programming language design mentioned at the course; various aspects of programming mentioned at the course; various programming languages where the concepts introduced at the course are implemented in a surprising or otherwise interesting way; etc.

17 TDT4165 Administratrivia contd Useful, though not obligatory, previous experience Discrete Mathematics (eg. TMA4140) Algorithms and Data Structures (eg. TDT4120) Logics Functional, Procedural, Object-Oriented (eg. TDT4100), and Logic Programming

18 TDT4165 Administratrivia contd Marginal Topics Compilation Introduction to languages other than Oz Software engineering, design patterns Algorithms, data structures, computational complexity

19 TDT4165 Administratrivia contd Platform We will program mostly in Oz using the Mozart system. Please install Mozart on your machines there are ports for many platforms; you can also use Mozart on machines in the labs or on the servers. Please read Mozart documentation for more on how to install and use the platform. Refer to for details. A brief introduction to Mozart and Oz will follow later during the lecture.

20 Lecture Outline TDT4165 Administratrivia Programming Languages Introduction Illustration Hello World Programs Further Comments Summary

21 Programming Languages What is programming? Broad sense: technical activities involved in the production of a program; analysis, design, and implementation. Narrow sense: coding (and testing) of programs for some given design. What is a language? Broadly: a systematic means of communication. Specifically: a programming language is a system for implementing algorithms as machine-executable programs.

22 Programming Languages contd Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning. Rick Cook If debugging is the art of removing bugs, then programming must be the art of inserting them. (anonymous)

23 Programming Languages contd A few questions How many programming languages are there? Which programming languages do you know? What are the features of the programming languages you know? What are the strong and weak sides of the languages you know?

24 Programming Languages contd Central issues Throughout the course we will repeatedly address these questions: What are the underlying ideas common to some, many, or all programming languages? What features can a programming language have? What are the benefits and dangers of introducing or eliminating any of these features? How can these features be combined to improve the languages, and which combinations are problematic?

25 Hello World! Hello World Programs (HWP) A Hello world program is a simple program that, when executed, displays the message Hello World!. There are collections of HWPs written in about any existing programming language. 2 Somewhat more interesting are the so-called 99 Bottles of Beer programs. 3 2 See, e.g., 3 See

26 Hello World! contd HWP examples We will use a few HWPs to motivate further discussion about programming languages. All examples have been tested on Ubuntu Linux. You will need to install suitable software (compilers, interpreters, etc.) in order to execute each program. You may also want to read, and need to modify, the makefile. Download the programs from the course s webpage, and read the instructions.

27 HWPs Further Comments The HWP examples are extremely simple, yet they illustrate some important issues with programming languages. In many programming languages, HWP look almost or completely identically. All HWP programs do (almost) the same, despite the differences in appearance. Programming languages can be compared and contrasted based on: their syntax and semantics; the mode of execution of programs; the target platform(s); supported programming paradigms; their development and standardization, etc.

28 HWPs Further Comments contd What is syntax? The syntax of a (programming) language is a set of rules defining which sequences of symbols are recognized as sentences, i.e., which constructs are legal in the language; a specification of the form of (programs in) the language. How can we specify the syntax of a programming language? How can we generate programs from a specification of the syntax? How can we automatically check whether a piece of code is a legal program, i.e., that it is syntactically valid?

29 HWPs Further Comments contd Syntactically, programming languages can be as similar as, e.g., Java, C, C++, and C#, or as different as, e.g., Fortran, Oz, Scheme, and F#. Example (Syntactic similarities and dissimilarities) int i = j + 10; print "hello" // Java, C, C++, C#? # Perl, Python, Ruby, Groovy? (define i (+ j 10)) ; Scheme declare i = j + 10 % Oz integer :: i = j + 10! Fortran let i = j + 10 (* F# *) lj10+si # dc is(x, J + 10), Prolog

30 HWPs Further Comments contd What is semantics? Semantics is a specification of the meaning of (programs in) the language, what a program does when executed. Semantics of a (programming) language can be specified by description, by calculus, by a set of rules defining what happens when a program is executed How can we specify the semantics of a programming language? How can we automatically check whether a program can actually be executed? How can we predict what will happen if a program is executed? A bit more difficult to compare the semantics of programming languages based on HWPs...

31 HWPs Further Comments contd How can a program be executed? Programs can be: compiled, then executed on the target machine; interpreted directly on the target machine; Hybrid approaches are also possible. Some languages are designed specifically for compilation (e.g., C); 4 others for interpretation (e.g., Python, Ruby); 5 yet others support both interpretation and compilation (e.g., Lisp, Haskell, Scala). 4 Interactive C interpreters do exist; see, e.g., 5 But there are jit-compiled versions of both languages, e.g., IronPython and IronRuby targetting the.net platform.

32 HWPs Further Comments contd What can the target machine be? The target machine that executes a program can be: the underlying hardware with its architecture compilation into and/or interpretation of programs in the machine language; a virtual machine, which interprets (or compiles into machine language) programs in the intermediate form of bytecode; an interpreter which operates directly on the source code with no preceding compilation. The execution of machine language code is dependent on a specific architecture (e.g., x86) and a specific operating system (e.g., Linux). The execution of intermediate bytecode requires a specific virtual machine (e.g., JVM, CLR, ozengine). Direct execution of source code requires a specific interpreter (e.g., irb, groovysh).

33 HWPs Further Comments contd Example (Modes of execution) # compile C code into native (machine) code # then execute native code on the machine $ gcc hello.c -o hello &&./hello # compile C# code into Common Intermediate Language (CIL) # then execute on the Common Language Runtime (CLR) $ mcs hello.cs && mono hello.exe # interpret Scheme code using a Scheme interpreter # (a Scheme virtual machine ) $ scm -l hello.scm

34 HWPs Further Comments contd What programming paradigms can a language support? The are a number of different programming paradigms and concepts available in different languages, e.g., object-oriented programming (OOP), declarative programming, functional programming, programming with lazy execution, concurrent programming, logic programming, etc. Programming languages can (and often do) support more than one programming paradigm. Some languages are purely one-paradigmatic, for example: Datalog (function-free logic queries), Smalltalk (all things are objects), Scheme?

35 HWPs Further Comments contd Example (Programming paradigms) Fortran is a typical imperative, procedural programming language. Ruby is a purely object-oriented programming language. Haskell is a purely functional programming language with lazy evaluation. Erlang is a language designed specifically for programming with concurrency. Prolog is a declarative, logic programming language. Oz is a multiparadigm programming language.

36 HWPs Further Comments contd How can a programming language be developed? A programming language can be the result of a community effort and undergo continuous evolution, or of a one-time centralized development project. Some languages have formal specifications and many compliant implementations, for others there is only one reference implementation which is the de facto (but not formal) specification. Some programming languages are developed to solve a specific problem, others are developed as general purpose programming languages.

37 HWPs Further Comments contd Example (Specification and development of PL) Fortran was originally developed by John W. Backus team at IBM, and initially had no standard specification, but newer versions of the language are backed by ISO standards. There are numerous Fortran compilers, which provide their own extensions to the language. Scheme was originally developed by Guy L. Steele and Gerald J. Sussman at MIT and has a precise specification of both its syntax and semantics (most recently, the 6th Revised Report on the Algorithmic Language Scheme, R 6 RS). There are numerous implementations of Scheme. Perl was originally developed by Larry Wall at NASA and has no written specification; there is only one implementation of the interpreter, and it is the de facto reference for the language. The first object-oriented language, Simula 67, was developed by Ole-Johan Dahl and Kristen Nygaard then at the Norwegian Computing Centre, to be able to model and simulate interacting entities.

38 Lecture Outline TDT4165 Administratrivia Programming Languages Introduction Illustration Hello World Programs Further Comments Summary

39 Summary This time Next time we illustrated some of the similarities and differences between programming languages with the extremely simple (if not silly) Hello World Program we shall introduce the Oz platform we shall briefly introduce some of the main programming paradigms we shall introduce a motivating example specify and implement a simple language for arithmetic computations on integers we will have a deeper look at how languages can be specified at the level of their syntax

40 Summary contd Homework Pensum Further reading Questions...?...?...? Please read the introductory chapter (Ch. 1) from CTMCP. Download, install, and play with the Mozart system. There is no pensum material for today, but you will need to be familiar with Oz and Mozart anyway consider reading the Oz tutorial. 6 See, e.g., Chapter 2 in Sebesta Concepts of Programming Languages for an interesting account of the evolution of major programming languages. 6 See