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;;; list.el --- Functions for working with lists. -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>
;;; Commentary:
;; Since I prefer having the `list/' namespace, I wrote this module to wrap many
;; of the functions that are defined in the the global namespace in ELisp. I
;; sometimes forget the names of these functions, so it's nice for them to be
;; organized like this.
;;
;; Motivation:
;; Here are some examples of function names that I cannot tolerate:
;; - `car': Return the first element (i.e. "head") of a linked list
;; - `cdr': Return the tail of a linked list
;; As are most APIs for standard libraries that I write, this is heavily
;; influenced by Elixir's standard library.
;;
;; Elixir's List library:
;; - ++/2
;; - --/2
;; - hd/1
;; - tl/1
;; - in/2
;; - length/1
;;
;; Similar libraries:
;; - dash.el: Functional library that mimmicks Clojure. It is consumed herein.
;; - list-utils.el: Utility library that covers things that dash.el may not
;; cover.
;; stream.el: Elisp implementation of streams, "implemented as delayed
;; evaluation of cons cells."
;; TODO: Consider naming this file linked-list.el.
;; TODO: Support module-like macro that auto-namespaces functions.
;; TODO: Consider wrapping most data structures like linked-lists,
;; associative-lists, etc in a `cl-defstruct', so that the dispatching by type
;; can be nominal instead of duck-typing. I'm not sure if this is a good idea
;; or not. If I do this, I should provide isomorphisms to map between idiomatic
;; ways of working with Elisp data structures and my wrapped variants.
;; TODO: Are function aliases/synonyms even a good idea? Or do they just
;; bloat the API unnecessarily?
;;; Code:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Dependencies
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; TODO: Move `prelude/assert' elsewhere so that I can require it without
;; introducing the circular dependency of list.el -> prelude.el -> list.el.
;;(require 'prelude)
(require 'dash)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Constants
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defconst list/tests? t
"When t, run the test suite.")
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Library
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun list/new ()
"Return a new, empty list."
'())
(defun list/concat (&rest lists)
"Joins `LISTS' into on list."
(apply #'-concat lists))
(defun list/join (joint xs)
"Join a list of strings, XS, with JOINT."
(if (list/empty? xs)
""
(list/reduce (list/first xs)
(lambda (x acc)
(string/concat acc joint x))
(list/tail xs))))
(defun list/length (xs)
"Return the number of elements in `XS'."
(length xs))
(defun list/get (i xs)
"Return the value in `XS' at `I', or nil."
(nth i xs))
(defun list/head (xs)
"Return the head of `XS'."
(car xs))
;; TODO: Learn how to write proper function aliases.
(defun list/first (xs)
"Alias for `list/head' for `XS'."
(list/head xs))
(defun list/tail (xs)
"Return the tail of `XS'."
(cdr xs))
(defun list/reverse (xs)
"Reverses `XS'."
(reverse xs))
(defun list/cons (x xs)
"Add `X' to the head of `XS'."
(cons x xs))
;; map, filter, reduce
;; TODO: Create function adapters like swap.
;; (defun adapter/swap (f)
;; "Return a new function that wraps `F' and swaps the arguments."
;; (lambda (a b)
;; (funcall f b a)))
;; TODO: Make this function work.
(defun list/reduce (acc f xs)
"Return over `XS' calling `F' on an element in `XS'and `ACC'."
(-reduce-from (lambda (acc x) (funcall f x acc)) acc xs))
;; TODO: Support this. It seems like `alist/set' is not working as I expected it
;; to. Perhaps we should add some tests to confirm the expected behavior.
;; (cl-defun list/index (f xs &key (transform (lambda (x) x)))
;; "Return a mapping of F applied to each x in XS to TRANSFORM applied to x.
;; The TRANSFORM function defaults to the identity function."
;; (->> xs
;; (list/reduce (alist/new)
;; (lambda (x acc)
;; (let ((k (funcall f x))
;; (v (funcall transform x)))
;; (if (alist/has-key? k acc)
;; (setf (alist-get k acc) (list v))
;; (setf (alist-get k acc) (list v))))))))
;; (prelude/assert
;; (equal '(("John" . ("Cleese" "Malkovich"))
;; ("Thomas" . ("Aquinas")))
;; (list/index (lambda (x) (plist-get x :first-name))
;; '((:first-name "John" :last-name "Cleese")
;; (:first-name "John" :last-name "Malkovich")
;; (:first-name "Thomas" :last-name "Aquinas"))
;; :transform (lambda (x) (plist-get x :last-name)))))
(defun list/map (f xs)
"Call `F' on each element of `XS'."
(-map f xs))
(defun list/map-indexed (f xs)
"Call `F' on each element of `XS' along with its index."
(-map-indexed (lambda (i x) (funcall f x i)) xs))
(defun list/filter (p xs)
"Return a subset of XS where predicate P returned t."
(list/reverse
(list/reduce
'()
(lambda (x acc)
(if (funcall p x)
(list/cons x acc)
acc))
xs)))
(defun list/reject (p xs)
"Return a subset of XS where predicate of P return nil."
(list/filter (lambda (x) (not (funcall p x))) xs))
(defun list/find (p xs)
"Return the first x in XS that passes P or nil."
(-find p xs))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Predicates
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun list/instance? (xs)
"Return t if `XS' is a list.
Be leery of using this with things like alists. Many data structures in Elisp
are implemented using linked lists."
(listp xs))
(defun list/empty? (xs)
"Return t if XS are empty."
(= 0 (list/length xs)))
(defun list/all? (p xs)
"Return t if all `XS' pass the predicate, `P'."
(-all? p xs))
(defun list/any? (p xs)
"Return t if any `XS' pass the predicate, `P'."
(-any? p xs))
(defun list/contains? (x xs)
"Return t if X is in XS using `equal'."
(-contains? xs x))
;; TODO: Support dedupe.
;; TODO: Should we call this unique? Or distinct?
;; TODO: Add tests.
(defun list/dedupe-adjacent (xs)
"Return XS without adjacent duplicates."
(prelude/assert (not (list/empty? xs)))
(list/reduce (list (list/first xs))
(lambda (x acc)
(if (equal x (list/first acc))
acc
(list/cons x acc)))
xs))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Tests
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; (when list/tests?
;; (prelude/assert
;; (= 0
;; (list/length '())))
;; (prelude/assert
;; (= 5
;; (list/length '(1 2 3 4 5))))
;; (prelude/assert
;; (= 16
;; (list/reduce 1 (lambda (x acc) (+ x acc)) '(1 2 3 4 5))))
;; (prelude/assert
;; (equal '(2 4 6 8 10)
;; (list/map (lambda (x) (* x 2)) '(1 2 3 4 5)))))
(provide 'list)
;;; list.el ends here
|
