A Clojure library inspired by Factor
The name "Factjor" is a mashup of "Factor" and "Clojure". It is pronounced "Fact-sure".
Stack languages have several very nice properties:
- Concatenation is function composition.
- Side effects occur from left to right.
- Complex pipelines can be constructed without naming values ("Point Free").
These properties enable traditionally side-effectual code to be converted into a pure function which returns a (potentially lazy) sequence of words comprising a concatenative program. Additionally, the linear nature of execution makes concatenative languages a natural fit for streaming protocols.
See also: Why Concatenative Programming Matters.
(require '[factjor.core :as cat :refer (defword)]) ;; Math is a terrible fit for concatenative languages, but it's easy to try. ;; The run function executes a queue of words and returns the stack after ;; execution. The stack is a normal Clojure list, whose head is the stack top. (cat/run 10 7 cat/-) ;=> (3) ;; You can define new words in terms of other words. ;; What looks like an argument list is actually just documentation. ;; It describes the "stack effect" of the word. ;; Sadly, 'cat// must be 'cat/div because of a Clojure reader bug. (defword avg2 [x y -- avg] cat/+ 2 cat/div) (cat/run 10 20 avg2) ;=> (15) ;; Sequences of words, called "quotations", enable higher-order words, ;; called "combinators". Use cat/call to invoke a quotation. (cat/run 5 [2 cat/+] cat/call) ;=> (7) (cat/run 5 10 [2 cat/+] cat/dip) ;=> (10 7) ;; Word objects can be applied early to curry values to the right: (cat/run 5 (cat/- 2)) ;=> 3
This project is just an experiment, so docs will remain thin. The experiment continues with DomScript, a concatenative library with jQuery-style API. I'll have Lots more to say about concatenative programming in the future, stay tuned.
Copyright © 2013 Brandon Bloom
Distributed under the Eclipse Public License, the same as Clojure.