code.delx.au - gnu-emacs-elpa/blob - avy.el

   1 ;;; avy.el --- set-based completion -*- lexical-binding: t -*-
   2
   3 ;; Copyright (C) 2015  Free Software Foundation, Inc.
   4
   5 ;; Author: Oleh Krehel
   6
   7 ;; This file is part of GNU Emacs.
   8
   9 ;; This file is free software; you can redistribute it and/or modify
  10 ;; it under the terms of the GNU General Public License as published by
  11 ;; the Free Software Foundation; either version 3, or (at your option)
  12 ;; any later version.
  13
  14 ;; This program is distributed in the hope that it will be useful,
  15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17 ;; GNU General Public License for more details.
  18
  19 ;; For a full copy of the GNU General Public License
  20 ;; see <http://www.gnu.org/licenses/>.
  21
  22 ;;; Commentary:
  23 ;;
  24 ;; This package provides a generic completion method based on building
  25 ;; a balanced decision tree with each candidate being a leaf. To
  26 ;; traverse the tree from the root to a desired leaf, typically a
  27 ;; sequence of `read-char' can be used.
  28 ;;
  29 ;; In order for `read-char' to make sense, the tree needs to be
  30 ;; visualized appropriately, with a character at each branch node. So
  31 ;; this completion method works only for things that you can see on
  32 ;; your screen, all at once:
  33 ;;
  34 ;; * character positions
  35 ;; * word or subword start positions
  36 ;; * line beginning positions
  37 ;; * link positions
  38 ;; * window positions
  39 ;;
  40 ;; If you're familiar with the popular `ace-jump-mode' package, this
  41 ;; package does all that and more, without the implementation
  42 ;; headache.
  43
  44 ;;; Code:
  45 (require 'cl-macs)
  46
  47 (defmacro avy-multipop (lst n)
  48   "Remove LST's first N elements and return them."
  49   `(if (<= (length ,lst) ,n)
  50        (prog1 ,lst
  51          (setq ,lst nil))
  52      (prog1 ,lst
  53        (setcdr
  54         (nthcdr (1- ,n) (prog1 ,lst (setq ,lst (nthcdr ,n ,lst))))
  55         nil))))
  56
  57 (defun avy-tree (lst keys)
  58   "Coerce LST into a balanced tree.
  59 The degree of the tree is the length of KEYS.
  60 KEYS are placed appropriately on internal nodes."
  61   (let ((len (length keys)))
  62     (cl-labels
  63         ((rd (ls)
  64            (let ((ln (length ls)))
  65              (if (< ln len)
  66                  (cl-pairlis keys
  67                              (mapcar (lambda (x) (cons 'leaf x)) ls))
  68                (let ((ks (copy-sequence keys))
  69                      res)
  70                  (dolist (s (avy-subdiv ln len))
  71                    (push (cons (pop ks)
  72                                (if (eq s 1)
  73                                    (cons 'leaf (pop ls))
  74                                  (rd (avy-multipop ls s))))
  75                          res))
  76                  (nreverse res))))))
  77       (rd lst))))
  78
  79 (defun avy-subdiv (n b)
  80   "Distribute N in B terms in a balanced way."
  81   (let* ((p (1- (floor (+ (log n b) 1e-6))))
  82          (x1 (expt b p))
  83          (x2 (* b x1))
  84          (delta (- n x2))
  85          (n2 (/ delta (- x2 x1)))
  86          (n1 (- b n2 1)))
  87     (append
  88      (make-list n1 x1)
  89      (list
  90       (- n (* n1 x1) (* n2 x2)))
  91      (make-list n2 x2))))
  92
  93 (defun avy-traverse (tree walker &optional recur-key)
  94   "Traverse TREE generated by `avy-tree'.
  95 WALKER is a function that takes KEYS and LEAF.
  96
  97 RECUR-KEY is used in recursion.
  98
  99 LEAF is a member of LST argument of `avy-tree'.
 100
 101 KEYS is the path from the root of `avy-tree' to LEAF."
 102   (dolist (br tree)
 103     (let ((key (cons (car br) recur-key)))
 104       (if (eq (cadr br) 'leaf)
 105           (funcall walker key (cddr br))
 106         (avy-traverse (cdr br) walker key)))))
 107
 108 (defun avy-read (tree display-fn cleanup-fn)
 109   "Select a leaf from TREE using consecutive `read-char'.
 110
 111 DISPLAY-FN should take CHAR and LEAF and signify that LEAFs
 112 associated with CHAR will be selected if CHAR is pressed.  This is
 113 commonly done by adding a CHAR overlay at LEAF position.
 114
 115 CLEANUP-FN should take no arguments and remove the effects of
 116 multiple DISPLAY-FN invokations."
 117   (catch 'done
 118     (while tree
 119       (avy-traverse tree display-fn)
 120       (let ((char (read-char))
 121             branch)
 122         (funcall cleanup-fn)
 123         (if (setq branch (assoc char tree))
 124             (if (eq (car (setq tree (cdr branch))) 'leaf)
 125                 (throw 'done (cdr tree)))
 126           (signal 'user-error (list "No such candidate" char))
 127           (throw 'done nil))))))
 128
 129 (provide 'avy)
 130
 131 ;;; avy.el ends here