A Quine in Forth

Originally published on: Tue, 04 Aug 2009 02:47:56 +0000

I needed a little mental exercise tonight, so I chose to write a quine ( a program that produces its own source as its output ) in the Forth programming language?

Why Forth? Because I'm a novice Forth programmer at best. I don't think very well in Forth, so this took some effort. Here's the quine: ( the source for this quine is in the public domain )

s" swap dup 1 type 34 emit 32 emit over over swap type 34 emit 32 emit swap type" swap dup 1 type 34 emit 32 emit over over swap type 34 emit 32 emit swap type

I tested the above in immediate mode in Win32Forth.

The first portion:

s" ... to the ending " leaves the address and length of a counted string on the stack. By following that with swap dup 1, I was able to make a counted version of the string with a length of 1. A call to the type word then displays the letter "s" from the beginning of the string "swap".

emit 34 emit 32 causes a double-quote and a space to appear. So, the only thing I have left to do is to display the string, a dquote and the string again and I'm done.

I do that by using the remaining code over over swap type 34 emit 32 emit swap type.

Unless otherwise noted, all code and text entries are Copyright Š2009 by James K. Lawless

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