Programming Languages:Introduction and Overview

Greg J. Badros

badros@cs.washington.edu

University of Washington, Seattle

CSE-341, Summer 1999

History ofProgramming Languages

1955

1960

1965

Fortran

Algol 60

Lisp

CPL

Snobol

History ofProgramming Languages

1965

1970

1975

BCPL

Algol 68

B

Prolog

C

Unix

rewritten

in C

Simula

Scheme

Smalltalk-72

History ofProgramming Languages

1975

1980

1985

K&R Published

The C Programming

Language

ANSI X3J11

convened to

standardize C

C with Classes

CPre

C++

Objective

C

Smalltalk-80

Icon

History ofProgramming Languages

1985

1990

1995

Stroustrup’s

The C++ Programming

Language

ANSI X3J16

Formed for

C++ Standard

Oak

Project

ARM

Published

C++ PL

2nd Ed.

Java

Haskell

Perl

Perl5

What is a programming language for?

• Instructing machines?

• Communicating among programmers?

• Expressing high level designs?

• Notation for algorithms?

• Tool for experimentation?Languages are for both humansand computers!

Effective Use of Programming Languages

“Learning the fundamentals of a programming language is one thing: learning how to design and write effective programs in that language is something else entirely.”

—Scott Meyers

Why do we care?

• Whorf-Sapir hypothesis for natural languages

• Tradeoffs among languages
  • reusability, maintainability
  • performance, robustness
  • flexibility, dynamicism
  • libraries
  • aesthetics (i.e., “fun-ness”)

Language classification

• Imperative (Fortran, Algol, C)

• Functional (“Pure” Scheme/Lisp, Haskell)

• Logic/Relational (Prolog)

• Object-oriented (Smalltalk, Java, C++)

• Languages may encourage a certain style even if they do not force it on you!

Complexity vs. Expressiveness

Complexity

Expressiveness

C

C++

Java

Scheme

Haskell

What’s wrong with imperative?

int i = 7;

printf("%d\n",i*2);

• What gets printed?

Assignments makereasoning difficult!

int i = 7;

i = 3;

printf("%d\n",i*2);

Are we safe yet?

const int i = 7;

/* no assignments in here */

printf("%d\n",i*2); /* 14? */

Imperative programming

• Nice for execution, translation… BUT:

• Harder for humans tounderstand and reason about

• Harder for sophisticated software tools
  • Proving correctness is harder
  • Restricts code motion, limits optimizer(especially important for parallel machines)

The Functional Approach

• Eliminates assignments (side effects),focus on expressions

• Tell what to compute, not how(leave order of computation unspecified)

• Higher level programming model—leave more details to machine

Scheme

• Very simple syntactically

• Still an imperative language, though

• But encourages a functional style

• Can write in a purely functional subset
  • we will do this in the beginning
  • still has assignments

• Dynamically typed

Haskell

• Pure functional language

• Statically-typed

• “Lazy” evaluation