programming-for-dummies

Teaching Languages 55
The Interactivity of BASIC Interpreters
One reason why programming in the old days
was so time-consuming was because you
could never run a program until you compiled
(translated) it into machine language. So if you
wrote a program in a language like COBOL, you
had to compile it into machine language first.
Not only were early compilers notoriously slow
(taking hours to compile even the simplest programs),
but compilers also required that you
write a complete program, even if you just
wanted to write a single command.
BASIC avoided this problem by using an interpreter
instead. Unlike a compiler that would
convert an entire program into machine language,
an interpreter would convert each command
into machine language and show you the
results of your command right away.
Because an interpreter could show you what
each command would do, you could see right
away if you typed a correct command or not.
Such instant feedback could help you catch on
to programming faster. Think how fast you can
understand a foreign language if you can practice
on someone sitting right in front of you.
Now think how fast you could understand a foreign
language if you had to write a letter to a
pen pal overseas and then wait three weeks for
a reply. That’s the difference between a compiler
in the old days (like writing and waiting for
a letter from overseas) and an interpreter (like
talking to someone face to face).
Nowadays, compilers are so fast that you can
get near-instant feedback with most programming
languages, so this initial advantage of
BASIC is no longer relevant. Almost all of today’s
versions of BASIC use a compiler instead of an
interpreter.
Book I
Chapter 3
Types of
Programming
Languages
Turtle graphics with Logo
BASIC introduced the idea of giving programmers instant feedback every
time they typed in another BASIC command. If you typed in the following
BASIC command:
PRINT 2+4
The BASIC interpreter would display the following on-screen:
6
Although giving programmers instant feedback made figuring out programming
easier, a computer scientist named Seymour Papert felt that programming
should be accessible to everyone, including children. Because few
children are excited about adding 2+4 together and seeing the number 6
appear, Seymour Papert thought that a better form of instant feedback for
children would involve seeing the results of your program visually.