TI1220 2012-2013Concepts of Programming Languages

Eelco Visser / TU Delft

Lecture 1: Programming Linguistics

Outline

Course Organization

Code of Conduct

Exams & Grades

Course Staff

Literature

Programming Linguistics

Why study PLs?

Syntax

Semantics

Code of Conduct

Inspired by Coursera Honor Code

I will not use electronic devices such as laptops, phones, or tablets during lectures.

Experimental exception: laptop for taking notes at last row

I will not enter the lecture hall once the lecture has started.

My answers to assignments and exams will be my own work (except for assignments that explicitly permit collaboration).

http://en.wikipedia.org/wiki/File:Plagiarism_vs_Copyright_Infringement.png

I will not make solutions to assignments and exams available to anyone else. This includes both solutions written by me, as well as any official solutions provided by the course staff.

http://ucblibraries.colorado.edu/about/images/Xerox5135.jpg

I will not engage in any other activities that will dishonestly improve my results or dishonestly improve/hurt the results of others.

Exams & Grades

Course Grade

Your final grade G for the course will be computed as follows:

G = (E * 0.6) + (GA * 0.4)

where E is your grade for the exam an GA is your grade for the graded assignments.

Graded Assignments

There will be four Graded Assignments.

For each you need to get at least a 4.0 to pass.

GA is the average of the four grades.

Exams

You can pass the exam in two ways:

Pass the midterm Q3 exam on April 9 with at least a 6.0 and then pass the Q4 exam on June 26 also with a 6.0. E is the average of two exams.

Pass the Q3+Q4 exam on June 26 with at least a 6.0

Pass the August resit with at least a 6.0

All assignments for this course are provided via WebLab and should be submitted via

WebLab, including the exams.

Exam/Lab Grades from 2011-2012

Partial result from 2011-2012?

Discuss with me offline(but not today)

Warning!This course moves from first year to

second year in new curriculum

TI1220 will not be taught in 2013-2014

Lab & exams will be repeated, no lectures

My advice: pass the course this year!

Course Staff

Course Staff

http://eelcovisser.org/wiki/about/officehours

Assistants• Jeff Smits• Victor Spiridon• Tim de Jong• Bastiaan Reijm

Instructors • Eelco Visser• Vlad Vergu

Literature

Course Notes on WebLab

Programming Linguistics

Why do we have so many programming languages?

Computers Process Data

computerdata data

Programmable Computers

computerdata data

program

Programming Language

computerdata data

L program

Turing Machines

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

Turing/Church Thesis: Every effective computation can be carried out by a Turing

machine (IN2505)

Why bother with new programming languages?

History of Programming Languages

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.

Programming Languages in TI @ TUD

TI1200: Object-Oriented Programming

• Java

TI1400: Computer Systems

• Assembly

TI1500: Web- and Database Technology

• HTML, PHP, SQL, JavaScript

TI1600: Multi-Agent Systems

• Prolog, GOAL

“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.

mov &a, &cadd &b, &cmov &a, &t1sub &b, &t1and &t1,&c

Source: http://sites.google.com/site/arch1utep/home/course_outline/translating-complex-expressions-into-assembly-language-using-expression-trees

c = ac += bt1 = at1 -= bc &= t1

c = (a + b) & (a - b)

From Instructions to Expressions

From Calling Conventions to Procedures

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

function definition and call in Scala

From Malloc to Garbage Collection

/* Allocate space for an array with ten elements of type int. */int *ptr = (int*)malloc(10 * sizeof (int));if (ptr == NULL) { /* Memory could not be allocated, the program should handle the error here as appropriate. */} else { /* Allocation succeeded. Do something. */ free(ptr); /* We are done with the int objects, and free the associated pointer. */ ptr = NULL; /* The pointer must not be used again, unless re-assigned to using malloc again. */}

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

int [] = new int[10];/* use it; gc will clean up (hopefully) */

Linguistic Abstraction

identify pattern

use new abstraction

language A language Bdesign abstraction

Domains of Computation

Application domains

Systems programming

Embedded software

Web programming

Enterprise software

Database programming

...

Why So Many Programming Languages?

Linguistic abstraction: better understanding of the general domain of computation

Specialization to domain: different requirements from different application domains

Why Study Programming Languages?

Language shapes thought: understand the languages that you are using

Choosing the right language for the job

Learning to learn new languages

Understanding implementation: what’s under the hood?

Topics in this Course

Syntax and SemanticsNames, Bindings, and Scopes Storage Data TypesFunctional ProgrammingType Systems 1: PolymorphismType Systems 2: Type Parameterization

Parsing and InterpretationControl AbstractionData Abstraction / Modular ProgrammingFunctional Programming ReduxConcurrencyConcurrent ProgrammingDomain-Specific Languages

How can we describe a programming language?

Syntax

Syntax

syntax |ˈsinˌtaks|nounthe arrangement of words and phrases to create well-formed sentences in a language: the syntax of English.• a set of rules for or an analysis of this: generative syntax.• the branch of linguistics that deals with this.

ORIGIN late 16th cent.: from French syntaxe, or via late Latin from Greek suntaxis, from sun- ‘together’ + tassein ‘arrange.’

Syntax

“The syntax of a programming language is the form of its expressions, statements,

and program units.”Sebesta Ch3

Lexical vs Context-free Syntax

lexical syntax

• words made from letters

• structure not relevant

• regular expressions

context-free syntax

• sentences made from words

• structure relevant

• context-free grammars

• Backus-Naur Form

• Extended Backus-Naur Form

Lexemes & Tokens

Lexemes are the words that make a sentences

Tokens are the categories of lexemes

Lexemes & Tokens

index = 2 * count + 17;

Lexeme Token

index Identifier

= EqualSign

2 IntegerLiteral

* MultOp

count Identifier

+ PlusOp

17 IntegerLiteral

; Semicolon

Describing Lexemes with Regular Expressions

Identifier: [A-Za-z][A-Za-z0-9]* IntegerLiteral: [0-9]+PlusOp: ‘+’Semicolon: ‘;’

Regular Expressions

basics

• strings: "nil"

• character classes: [a-zA-Z]

combinators

• concatenation: E1 E2

• optional: E?

• zero or more: E*

• one or more: E+

• alternative: E1 | E2

Describing Structure with Railroad Diagrams

Chomsky Hierarchy

http://www.cs.nott.ac.uk/~txa/g51mal.2001/notes/img4.png

BNF: Backus-Naur Form

Ambiguous Grammar

<assign> -> <id> = <expr><id> -> A | B | C<expr> -> <expr> + <expr> | <expr> * <expr> | ( <expr> ) | <id>

Unambiguous Grammar

<assign> -> <id> = <expr><id> -> A | B | C<expr> -> <expr> + <term> | <term><term> -> <term> * <factor> | <factor><factor> -> ( <expr> ) | <id>

Syntax in this Course

You should be able to determine whether a program is syntactically correct according to a context-free grammar (BNF, railroad diagram)

(There will be exercises on WebLab)

Millionaire's Corner

€€€€€€€€€

€€€€€€€€€

Demonstration ofDeclarative Syntax Definition in the

Spoofax Language Workbench

Semantics

Semantics

semantics |səәˈmantiks|pluralnoun [ usu. treated as sing. ]the branch of linguistics and logic concerned with meaning. There are a number of branches and subbranches of semantics, including formal semantics, which studies the logical aspects of meaning, such as sense, reference, implication, and logical form, lexical semantics, which studies word meanings and word relations, and conceptual semantics, which studies the cognitive structure of meaning.• the meaning of a word, phrase, sentence, or text: such quibbling over semantics may seem petty stuff.

DERIVATIVESsemantician |ˌsēmanˈtiSHəәn|noun,semanticist noun

Semantics

“The semantics of a programming language is the meaning of its expressions,

statements, and program units.”Sebesta Ch3

Static vs Dynamic Semantics

Static Semantics: (context-senstive) restriction of the set of valid programs

Dynamic Semantics: run-time behaviour of a program

Operational Semantics

Operational semantics: describe the meaning of a statement or program by specifying the effects of running it on a

machine

In second part of course (Q4): write interpreter for small functional language

Denotational Semantics

a denotational semantics defines a mapping from the syntactic domain to a semantic

domain of mathematical objects

M(‘0’) = 0M(‘1’) = 1M(<bin> ‘0’) = 2 * M(<bin>)M(<bin> ‘1’) = 2 * M(<bin>) + 1

<bin> -> ‘0’ | ‘1’ | <bin> ‘0’ | <bin> ‘1’

Axiomatic Semantics

axiomatic semantics specifies what can be proven about a program

{x > 3} x = x - 3 {x > 0}

Semantics in this Course

Informal operational semantics: Reasoning about the operational behavior of

programs

Comparative/translational semantics: Explaining the semantics of construct/concept

by translating it to another language

Reading & Programming in Week 1

Reading: Sebesta

Chapter 1: Preliminaries

Chapter 2: Evolution of the major programming languages (read)

Chapter 3: Describing Syntax and Semantics

Week 2: Names, Bindings, and Scope (Chapter 5)

WebLab: Scala Tutorial