||| Three Pipes |||

Three pipes is a stack language built to run inside of and in accord with Emacs Lisp.

Three pipes resembles Forth or Factor, (more the latter) in that it is a concatenative language where juxtaposition represents COMPOSITION of functions. That is the academic explanation. The Joy of concatenative languages is their great terseness and, regularity, and expressiveness. Stack languages are more Lispy than Lisp! Now all that power is right in your Emacs Lisp code:

(||| 4 4 +) ; -> 8

(||| "Hello World!" 10 
    ((dup <1>insert) dip 1 - dup 0 >) loop-while)
;; prints "Hello World" ten times

Usage

Put three-pipes.el on your load-path and then (require 'three-pipes).

Basic Syntax

The entry point for Three Pipes is three pipes:|||. The body of the three pipes macro is treated as a list of three pipes words. Atoms simply denote words which push themselves onto the stack. Regular symbols denote a three pipes word, a function which works a side effect on the stack, and special symbols of the form <integer>symbol-name, denote "glue words" which tell the compiler that you want to call the Emacs Lisp function symbol-name with integer arguments from the stack, and have the result pushed onto the stack.

For instance:

(||| "Raining " "cats " "and " "dogs." <4>concat)
;;; -> "Raining cats and dogs."

Lists are read as quotations, delayed three pipes programs which can be executed with the three pipes word call:

(||| 3 (+ 2) call) ;;; -> 5

One may optionally quote such lists:

(||| 3 '(+ 2) call) ;;; -> 5

Backquote can be used to splice values from the environment into the three-pipes code:

(let ((x 10)) (||| `,x 3 +)) ;;; -> 13

And hence to side effect values in the environment as well.

Words

Three pipes supports a small vocabulary of built in words:

dup dip swap if loop-while drop + - * / = equal eql concat append
cons map reduce reduce-init filter

And more words can be defined with the macros

3p-define-word 
3p-define-word-in-lisp

The former allows you to define new words in terms of three pipes programs while the latter allows you to use the primitive lisp functions 3p-push and 3p-pop as well as |||- which executes a fragment of three pipes code without resetting the context, to define new words in elisp. I plan on adding lots of words soon.