Factor: an extensible interactive language
Why Hacker News recommends it
HN recommends it as the best introduction to Factor and concatenative programming, with commenters saying it impressed them with the engineering.
What it is
A 2008 Google Tech Talk in which Slava Pestov introduces Factor, a concatenative language influenced by Forth, Lisp and Smalltalk. It covers the interactive environment, metaprogramming, and the language's modern high-level features and libraries.
Recommended by 5 HN commenters across 5 different months, 2014 to 2025.
What Hacker News said
Strong rec xelxebar · 2018-10 · on “Concatenative language (2017)”
I just stumbled across this Google Tech Talk on [factor][0] last night! It absolutely blew my mind. The engineering looks to be top notch, and the video is 9 years old to boot! [this video] Anyway, really want to give Factor a try for some personal projects. Would love to hear anecdotes from people who futz with this stuff. [0]: [LINK]
Strong rec fud101 · 2025-12 · on “Ask HN: Why did Python fail to evolve?”
It's funny because 3 dropped in 2008, the same year Slava was demonstrating Factor in google tech talks which was a contemporary language to python3 that completely blew Python out of the water. [this video]
Recommends agumonkey · 2014-01 · on “K, by Arthur Whitney (2005)”
I see what you did there. ps: just in case here's a very enjoyable talk, not about, but by Slava [this video] Beautiful and impressive.
Recommends benhoyt · 2020-01 · on “Factor: A Practical Stack Languge”
As someone who built Forth compilers back in the day, I really like this language. There's a nice overview of Factor as a paper here: [LINK] and a Google tech talk video of Slava Pestov (Factor's creator) showing off the language here: [this video]
Recommends johnisgood · 2025-08 · on “The V Programming Language”
I agree. I remember his talk on Factor. I wish people gave enough support back then so he could work on it full-time. Here is his talk on Factor: [this video] , back from 2008.
Cites runeks · 2014-09 · on “Pipes and Filters”
I recently came across a language called Factor that works very similar, if not identical, to this. Here's a video about it: [this video]
Cites zoltar · 2024-02 · on “Thinking Forth: A Language and Philosophy for Solving Problems (2004) [pdf]”
There was always something I liked about Forth when I didn't have to do much stack-thinking. One of the things that felt forth-y to me when I first encountered it was threaded code in Clojure (or any other point-free kind of idiom for that matter). [LINK] I'll sometimes abuse Python's compose to do similar things I won't send out for code review. Maybe I really should just try to live in Coconut instead of silly stuff like: import chess import chess.svg from IPython.display import SVG, display from functools import reduce def rcompose(*fs): return reduce(lambda f, g: lambda *xs, **ys: g(f(*xs, **ys)), fs) inline_board = rcompose( chess.Board, chess.svg.board, SVG, display) Factor's quotation
Cites johnisgood · 2025-09 · on “Evolving the OCaml Programming Language (2025) [pdf]”
Your comment does not make much sense even if it is true. Factor (Forth-like language) implements even its own ":" (defines a word, i.e. a function) using the language itself, it is not builtin, same with "if", and so forth. Thus, "MEMO:" or locals[1] ("::") being implemented as a library does not mean it is a bad thing, on the contrary, in the case of Factor, it makes it quite powerful. The object system is entirely implemented in Factor, too. "Large chunks of functionality are not part of the core language, they are in just as library".[2] And to compare OCaml's type system to Python's is straight out absurd. [1] Locals are entirely implemented in Factor, too, which is only about ~500 line