CS 403

Programming Language Theory

Class 2 - August 29, 2000

SyllabusTexts: Sebesta: most of the content & theoryEverybody has a copy?

Meyers: specific applications to C++ CDBookstore is getting the CD in…

Homework Assignment

List all the languages you have easy access to now. Engineering labs Bama Your home PC, if relevant Other computers…

Be sure to note the different implementations of each language.Due today. Turn it in now.Outside write: Name, Section 1 or 2

Homework Assignment #2 (1)Consider this program:

#include <stdio.h> main() {

int i;printf(“Value of i: %d, %o, %x, %u, \n %c, %f, %ld\

n", i,i,i,i,i,i,i);i = 42;printf(“Value of i: %d, %o, %x, %u, \n %c, %f, %ld\

n", i,i,i,i,i,i,i);

}

Homework Assignment #2 (2)

Compile and run (on 4 C compilers, including cc and gcc on UNIX)…Print your program and the executions, identified by compiler. Explain the output (about 1-2 pages) What does ‘printf’ do, and what do the ‘%’

commands do? Why the different but consistent output

values for the same variable? What differences do you note across

compilers?

Turn in Tuesday, Sept 5th

Reading QuizName one language in chapter 2 you hadn’t heard of before, and one characteristic of that language.After you’ve written your answer, draw a line & confer with your table-mates. Correct your answer if necessary.We won’t take this up today. (I’ve already got enough to grade!)

Primary Influences on

Language Design

• Computer architecture

• Programming methodologies

Computer Architecture

We use imperative languages,

at least in part, because we

use von Neumann machines.

Other architectures influence

other languages, i.e., LISP

machines, …

Programming Methodologies• 1950s and early 1960s: Simple

applications; worry about machine efficiency

• Late 1960s: People efficiency became important; readability, better control structures

• Late 1970s: Data abstraction• Middle 1980s: Object-oriented

programming

Language Categories1. Imperative

2. Functional

3. Logic

4. Object-oriented (closely

related to imperative)

Language Design Trade-Offs1. Reliability versus cost of

execution

2. Writability versus readability

3. Flexibility versus safety

Implementation Methods1. Compilation

• Translate high-level program to machine code

• Slow translation• Fast execution

2. Pure interpretation• No translation• Slow execution• Becoming rare

3. Hybrid implementation systems• Small translation cost• Medium execution speed

Programming EnvironmentsThe collection of tools used in software development1. UNIX – An old operating system and tool

collection2. Borland C++ – A PC environment for C

and C++3. Smalltalk –A language processor/

environment4. Microsoft Visual C++ – A large, complex

visual environment

Chapter 2: Evolution of Programming Languages (1)

Plankalkül - 1945Pseudocodes - 1949Laning and Zierler System - 1953FORTRAN:

I - 1957; II - 1958; IV - 1960-62; 77 - 1978; 90 - 1990

Language Evolution(2)LISP - 1959

ALGOL 58 - 1958;

60 - 1960

COBOL - 1960

BASIC - 1964

PL/I - 1965

Language Evolution (3): Early Dynamic Languages

SIMULA 67 - 1967

ALGOL 68 - 1968

Pascal - 1971

C - 1972

Prolog - 1972

Ada - 1983

Smalltalk - 1972-80

C++ - 1985

Java - 1995

Plankalkül - 1945Never implemented

Advanced data structures floating point, arrays, records

Invariants

Notation: A(7) := 5 * B(6) | 5 * B => A V | 6 7 (subscripts) S | 1.n 1.n (data types)

Pseudocodes - 1949Before pseudocodes machine codesWhat’s wrong with machine code? Poor readability Poor modifiability Expressions are tedious Machine weaknesses: no indexing,

floating point, ...

Pseudocodes:Short Code ‘49 Expressions were coded, left to

right

Speedcoding ‘54 Two weeks of programming

few hours! Automatically increment the

instruction counter

FORTRAN 0 - 1954

New IBM 704 Index registers Floating point in hardware

Environment of development:1. Computers were small and unreliable

2. Applications were scientific

3. No programming methodology or tools

4. Machine efficiency was most important

FORTRAN 0 / I - 1957Impact of environment on design:1. No need for dynamic storage

2. Need good array handling and counting loops

3. No string handling, decimal arithmetic, or powerful input/output (commercial stuff)

FORTRAN I - 1957First implemented version of FORTRAN

Names could have up to six characters

Posttest counting loop (DO)

Formatted I/O

User-defined subprograms

Three-way selection statement (arithmetic IF)

No data typing statements

FORTRAN I Features (cont.)No separate compilation

Compiler released in April 1957, after 18 worker/years of effort.

Programs larger than 400 lines rarely compiled correctly, mainly due to poor reliability of the 704 hardware.

Code was very fast

Quickly became widely used

FORTRAN II - 1958Independent compilation

Fix the bugs

FORTRAN IV - 1960-62Explicit type declarations

Logical selection statement

Subprogram names could be parameters

ANSI standard in 1966

FORTRAN 77 - 1978Character string handling

Logical loop control statement

IF-THEN-ELSE statement

FORTRAN 90 (“9X”) - 1990ModulesDynamic arraysPointersRecursionCASE statementParameter type checking

FORTRAN Evaluation:

Dramatically changed forever the way computers are used!

LISP - 1959LISt Processing language (MIT, McCarthy)

AI research needed a language that:

1. Process data in lists (vs. arrays)

2. Symbolic computation (vs. numeric)

Only two data types: atoms and lists

Syntax is based on lambda calculus

LISP (2)Pioneered functional programmingNo need for variables or assignmentControl via recursion and conditional expressionsStill the dominant language for AICOMMON LISP and Scheme are contemporary dialects of LISPML, Miranda, and Haskell are related languages

ALGOL 58 - 1958Environment of development:

1. FORTRAN had (barely) arrived for IBM 70X

2. Many other languages were being developed, all for specific machines

3. No portable language; all were machine-dependent

4. No universal language for communicating algorithms

ALGOL 58 (2)ACM and GAMM met for four days for design

Goals of the language:

1. Close to mathematical notation

2. Good for describing algorithms

3. Must be translatable to machine code

ALGOL 58 (3)Language Features:

Concept of type was formalized

Names could have any length

Arrays could have any number of subscripts

Parameters were separated by mode (in & out)

Subscripts were placed in brackets

Compound statements (begin ... end)

Semicolon as a statement separator

Assignment operator was :=

if had an else-if clause

ALGOL 60 - 1960Modified ALGOL 58 at 6-day meeting in Paris

New Features: Block structure (local scope) Two parameter passing methods Subprogram recursion Stack-dynamic arrays Still no i/o and no string handling

ALGOL 60 (2)

Successes:

It was the standard way to publish algorithms for over 20 years

All subsequent imperative languages are based on it

First machine-independent language

First language whose syntax was formally defined (BNF)

ALGOL 60 (3)Never widely used, especially in U.S.Reasons:

1. No I/O and the character set made programs nonportable

2. Too flexible--hard to implement3. Entrenchment of FORTRAN4. Formal syntax description5. Lack of support of IBM