The A-Z of Programming Languages: Forth

Charles H. Moore talks about the origins of Forth and how it shows that a computer language can be simple and powerful.

Computerworld is undertaking a series of investigations into the most widely-used programming languages. Previously we have spoken to Alfred v. Aho of AWK fame, S. Tucker Taft on the Ada 1995 and 2005 revisions, Microsoft about its server-side script engine ASP, Chet Ramey about his experience maintaining Bash, and Bjarne Stroustrup of C++ fame.

In this article we chat to Charles H. Moore about the design and development of Forth. Moore invented Forth while at the US National Radio Astronomy Observatory to help control radio telescopes and data-collection/reduction systems.

Here he chats about why Forth was invented, as well as why he still works with Forth today.

How did Forth come into existence?

Forth came about when I was faced with a just-released IBM 1130 minicomputer. Compiling a Fortran program was a cumbersome procedure involving multiple card decks. I used Fortran to develop the first Forth, which could use the disk and graphics display that Fortran couldn't. Because it was interactive, my programming was much faster and easier.

Was there a particular problem you were trying to solve?

This computer was at Mohasco Industries. Their main product was carpet and the problem was to determine if the 1130 could help design carpets. Forth was great for programming the 2250 display, but ultimately the lack of color doomed the project.

Did you face any hard decisions in the development of the language?

The hardest decision in developing Forth was whether to do it. Languages were not casually designed. It was reputed to require a brilliant team and man-years of effort. I had my eye on something quick and simple.

I write Forth code every day. It is a joy to write a few simple words and solve a problem. As brain exercise it far surpasses cards, crosswords or Sudoku; and is useful.

How did Forth get its name?

I decided to call it Fourth, as in 4th-generation computer language. But the 1130 file system limited names to 5 characters, so I shortened it to Forth. A fortuitous choice, since Forth has many positive associations.

I have read that Forth was developed from your own personal programming system, which you began to develop in 1958. Can you tell us a little more about this?

My personal programming system was a deck of punch cards, [now] sadly lost. It had a number of Fortran subroutines that did unformatted input/output, arithmetic algorithms and a simple interpreter. It let me customize a program via its input at a time when recompiling was slow and difficult.

Why did you incorporate Reverse Polish notation into the language?

Reverse Polish notation is the simplest way to describe arithmetic expressions. That's how you learn arithmetic in grade school, before advancing to infix notation with Algebra. I've always favored simplicity in the interest of getting the job done.

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