The computer programming language Forth was invented by Charles H. Moore in 1970. Forth is famous for being stack based and using reverse polish notation: the operators come after their operands. A Forth program to convert from Fahrenheit to Celsius (C = (F-32) × 5/9) is:

32 - 5 * 9 /

On 23rd August 2016 I had an urge to write a Forth system in 64-bit Intel Assembly. This talk is about what happens next.

In it I unpack what it means to implement a language. I dig a little into a lower-level description of typical computer hardware, and a little into 64-bit Intel Assembly. Compared to Python, Forth is a low-level language; compared to Assembly, Forth is a high-level language.

I'll talk about how we can implement one language in terms of another, by building models, and how we can model languages and model computational processes.

Forth is a tiny, but powerful, language. Moore's insight was to discover a language that was: - small; - sufficient; - easy to implement; - extensible.

The result is that Forth implementations are typically composed of a tiny nucleus (typically in Assembly) surrounded by a larger amount of "Forth-in-Forth".

Come. Let's implement a language.