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|
;;; vector.el --- Working with Elisp's Vector data type -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>
;;; Commentary:
;; It might be best to think of Elisp vectors as tuples in languages like
;; Haskell or Erlang.
;;
;; Not surprisingly, this API is modelled after Elixir's Tuple API.
;;
;; Some Elisp trivia:
;; - "Array": Usually means vector or string.
;; - "Sequence": Usually means list or "array" (see above).
;;
;; It might be a good idea to think of Array and Sequence as typeclasses in
;; Elisp. This is perhaps more similar to Elixir's notion of the Enum protocol.
;;
;; Intentionally not supporting a to-list function, because tuples can contain
;; heterogenous types whereas lists should contain homogenous types.
;;; Code:
;; TODO: Consider supporting an alias named tuple for vector.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Library
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defconst vector/enable-tests? t
"When t, run the tests defined herein.")
;; TODO: Consider labelling variadic functions like `vector/concat*'
;; vs. `vector/concat'.
(defun vector/concat (&rest args)
"Return a new vector composed of all vectors in `ARGS'."
(apply #'vconcat args))
;; TODO: Here's a sketch of a protocol macro being consumed.
;; (definstance monoid vector
;; :empty (lambda () []))
(defun vector/prepend (x xs)
"Add `X' to the beginning of `XS'."
(vector/concat `[,x] xs))
(defun vector/append (x xs)
"Add `X' to the end of `XS'."
(vector/concat xs `[,x]))
(defun vector/get (i xs)
"Return the value in `XS' at index, `I'."
(aref xs i))
(defun vector/set (i v xs)
"Set index `I' to value `V' in `XS'.
Returns a copy of `XS' with the updates."
(let ((copy (vconcat [] xs)))
(aset copy i v)
copy))
(defun vector/set! (i v xs)
"Set index `I' to value `V' in `XS'.
This function mutates XS."
(aset xs i v))
(when vector/enable-tests?
(let ((xs [1 2 3])
(ys [1 2 3]))
(prelude/assert (= 1 (vector/get 0 ys)))
(vector/set 0 4 ys)
(prelude/assert (= 1 (vector/get 0 ys)))
(prelude/assert (= 1 (vector/get 0 xs)))
(vector/set! 0 4 xs)
(prelude/assert (= 4 (vector/get 0 xs)))))
;; TODO: Decide between "remove" and "delete" as the appropriate verbs.
;; TODO: Implement this.
;; (defun vector/delete (i xs)
;; "Remove the element at `I' in `XS'.")
(provide 'vector)
;;; vector.el ends here
|
