programming-for-dummies

Scripting Languages 73
2. From the computer’s point of view, the original LISP command now
looks like this:
(list “Hello world”)
This command now displays the following on-screen:
(“Hello world”)
So the command
Book I
Chapter 3
Types of
Programming
Languages
(list (print “Hello world”))
prints the following:
“Hello world”
(“Hello world”)
In the previous example, LISP treats the (print “Hello world”) list first
as a command (to print “Hello world” on-screen) and then as data to feed
into the list command to display the list (“Hello world”) on-screen.
With traditional programming languages, like C or BASIC, commands and
data are separate where data may change but commands never change. With
LISP, a list can be both a command and data. That makes it possible for a
program to change its lists (treated either as data or as a command), essentially
allowing a program to modify itself while running, which can mimic the
learning and thinking process of a human being.
As you can see, both LISP and Prolog offer radically different ways to program
a computer compared to C or BASIC. Just as languages, like C and
BASIC, free you from the tedium of manipulating registers and memory
addresses to program a computer, so do LISP and Prolog free you from the
tedium of writing explicit step-by-step instructions to program a computer.
Although the idea that a LISP program can modify its own commands might
seem like science fiction, LISP is actually the second oldest programming language
still in use today. (FORTRAN is the oldest programming language still in
popular use.) LISP was invented in 1958, and although it’s been used primarily
as a research tool, people have created commercial programs using LISP.
Scripting Languages
Languages, such as C and C++, are often dubbed system programming languages
because they can create programs that access and manipulate the
hardware of a computer, such as an operating system (Linux and Windows)
or a utility program (an antivirus or anti-spyware program). However, using
systems programming languages, like C++, for everything can get clumsy.