Concatenative styles are making the rounds lately including some interesting examples in Clojure and Haskell. Now I’m perpetually drawn to concatenative languages and their ideas, so I wanted to know what it would take to provide a minimally representative concatenative experience in Clojure.1 As it turns out… not much:
(defn postfix [& e] (reduce #(if (fn? %2) (let [[l r & m] %] (cons (%2 r l) m)) (cons %2 %))  e))
This is how it’s used:
(postfix 5 1 2 + 4 * + 3 -) ;;=> 
The way that it works is that it treats every non-function as a value and every function as a binary function taking two elements off of a “stack”. It then wraps the answers back up onto the “top” of the stack. The final answer is the stack itself.
This is in no way indicative of a fully blown representation of concatenative programming languages,2 but it was fun and it highlights the stark simplicity of the model. This is my year to finally take concatenative languages seriously. I plan to study hard. I hope you’ll join me.
if you want to talk concatenative languages or pesto5, then feel free to comment below or email me at the address at the top of my blog