105 lines
3.1 KiB
EmacsLisp
105 lines
3.1 KiB
EmacsLisp
;;; cycle.el --- Simple module for working with cycles. -*- lexical-binding: t -*-
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;; Author: William Carroll <wpcarro@gmail.com>
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;;; Commentary:
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;; Something like this may already exist, but I'm having trouble finding it, and
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;; I think writing my own is a nice exercise for learning more Elisp.
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;;; Code:
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(require 'struct)
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(require 'math)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Wish list
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; - TODO: Provide immutable variant.
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;; - TODO: Replace mutable consumption with immutable variant.
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;; - TODO: Replace indexing with (math/mod current cycle).
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Library
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; `current-index' tracks the current index
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;; `xs' is the original list
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(cl-defstruct cycle current-index xs)
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(defun cycle/new (&rest xs)
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"Create an empty cycle."
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(make-cycle :current-index 0
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:xs xs))
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(defun cycle/from-list (xs)
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"Create a cycle from a list of `XS'."
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(make-cycle :current-index 0
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:xs xs))
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(defun cycle/to-list (xs)
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"Return the list representation of a cycle, XS."
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(cycle-xs xs))
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(defun next-index<- (lo hi x)
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"Return the next index in a cycle when moving downwards.
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- `LO' is the lower bound.
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- `HI' is the upper bound.
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- `X' is the current index."
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(if (< (- x 1) lo)
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(- hi 1)
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(- x 1)))
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(defun next-index-> (lo hi x)
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"Return the next index in a cycle when moving upwards.
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- `LO' is the lower bound.
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- `HI' is the upper bound.
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- `X' is the current index."
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(if (>= (+ 1 x) hi)
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lo
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(+ 1 x)))
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(defun cycle/prev (cycle)
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"Return the previous value in `CYCLE' and update `current-index'."
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(let* ((current-index (cycle-current-index cycle))
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(next-index (next-index<- 0 (cycle/count cycle) current-index)))
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(setf (cycle-current-index cycle) next-index)
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(nth next-index (cycle-xs cycle))))
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(defun cycle/next (cycle)
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"Return the next value in `CYCLE' and update `current-index'."
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(let* ((current-index (cycle-current-index cycle))
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(next-index (next-index-> 0 (cycle/count cycle) current-index)))
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(setf (cycle-current-index cycle) next-index)
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(nth next-index (cycle-xs cycle))))
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(defun cycle/current (cycle)
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"Return the current value in `CYCLE'."
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(nth (cycle-current-index cycle) (cycle-xs cycle)))
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(defun cycle/count (cycle)
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"Return the length of `xs' in `CYCLE'."
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(length (cycle-xs cycle)))
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(defun cycle/jump (i cycle)
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"Jump to the I index of CYCLE."
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(setf (cycle-current-index cycle)
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(math/mod i (cycle/count cycle)))
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cycle)
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(defun cycle/focus (p cycle)
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"Focus the element in CYCLE for which predicate, P, is t."
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(let ((i (->> cycle
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cycle-xs
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(-find-index p))))
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(if i
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(cycle/jump i cycle)
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(error "No element in cycle matches predicate"))))
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(defun cycle/contains? (x xs)
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"Return t if cycle, XS, has member X."
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(->> xs
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cycle-xs
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(list/contains? x)))
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(provide 'cycle)
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;;; cycle.el ends here
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