7410928b5b
More Elisp packaging :) Change-Id: I4cf5695fd97ed922b8dfe698a168061042208c73 Reviewed-on: https://cl.tvl.fyi/c/depot/+/6001 Reviewed-by: wpcarro <wpcarro@gmail.com> Autosubmit: wpcarro <wpcarro@gmail.com> Tested-by: BuildkiteCI
78 lines
2.3 KiB
EmacsLisp
78 lines
2.3 KiB
EmacsLisp
;;; bag.el --- Working with bags (aka multi-sets) -*- lexical-binding: t -*-
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;; Author: William Carroll <wpcarro@gmail.com>
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;; Version: 0.0.1
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;; Package-Requires: ((emacs "24.3"))
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;;; Commentary:
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;; What is a bag? A bag should be thought of as a frequency table. It's a way
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;; to convert a list of something into a set that allows duplicates. Isn't
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;; allowing duplicates the whole thing with Sets? Kind of. But the interface
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;; of Sets is something that bags resemble, so multi-set isn't as bad of a name
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;; as it may first seem.
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;;
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;; If you've used Python's collections.Counter, the concept of a bag should be
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;; familiar already.
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;;
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;; Interface:
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;; - add :: x -> Bag(x) -> Bag(x)
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;; - remove :: x -> Bag(x) -> Bag(x)
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;; - union :: Bag(x) -> Bag(x) -> Bag(x)
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;; - difference :: Bag(x) -> Bag(x) -> Bag(x)
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;;; Code:
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Dependencies
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(require 'al)
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(require 'list)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Library
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(cl-defstruct bag xs)
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(defun bag-new ()
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"Create an empty bag."
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(make-bag :xs (al-new)))
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(defun bag-from-list (xs)
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"Map a list of `XS' into a bag."
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(->> xs
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(list-reduce (bag-new) #'bag-add)))
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(defun bag-add (x xs)
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"Add X to XS."
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(if (bag-contains? x xs)
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(struct-update
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bag xs (lambda (xs) (al-update x (lambda (x) (+ 1 x)) xs)) xs)
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(struct-update bag xs (lambda (xs) (al-set x 1 xs)) xs)))
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(defun bag-remove (x xs)
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"Remove X from XS.
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This is a no-op is X doesn't exist in XS."
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(when (bag-contains? x xs)
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(struct-update bag xs (lambda (xs) (al-delete x xs)) xs)))
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(defun bag-count (x xs)
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"Return the number of occurrences of X in XS."
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(al-get x (bag-xs xs) 0))
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(defun bag-total (xs)
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"Return the total number of elements in XS."
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(->> (bag-xs xs)
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(al-reduce 0 (lambda (_key v acc) (+ acc v)))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Predicates
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(defun bag-contains? (x xs)
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"Return t if XS has X."
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(al-has-key? x (bag-xs xs)))
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(provide 'bag)
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;;; bag.el ends here
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