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;;; gap-buffer.scm --- String buffer that supports point
;;; Copyright (C) 2002, 2003, 2006 Free Software Foundation, Inc.
;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;;
;;; Author: Thien-Thi Nguyen <ttn@gnu.org>
;;; Commentary:
;; A gap buffer is a structure that models a string but allows relatively
;; efficient insertion of text somewhere in the middle. The insertion
;; location is called `point' with minimum value 1, and a maximum value of the
;; length of the string (which is not fixed).
;;
;; Specifically, we allocate a continuous buffer of characters that is
;; composed of the BEFORE, the GAP and the AFTER (reading L->R), like so:
;;
;; +--- POINT
;; v
;; +--------------------+--------------------+--------------------+
;; | BEFORE | GAP | AFTER |
;; +--------------------+--------------------+--------------------+
;;
;; <----- bef-sz ----->|<----- gap-sz ----->|<----- aft-sz ----->
;;
;; <-------------------| usr-sz |------------------->
;;
;; <-------------------------- all-sz -------------------------->
;;
;; This diagram also shows how the different sizes are computed, and the
;; location of POINT. Note that the user-visible buffer size `usr-sz' does
;; NOT include the GAP, while the allocation `all-sz' DOES.
;;
;; The consequence of this arrangement is that "moving point" is simply a
;; matter of kicking characters across the GAP, while insertion can be viewed
;; as filling up the gap, increasing `bef-sz' and decreasing `gap-sz'. When
;; `gap-sz' falls below some threshold, we reallocate with a larger `all-sz'.
;;
;; In the implementation, we actually keep track of the AFTER start offset
;; `aft-ofs' since it is used more often than `gap-sz'. In fact, most of the
;; variables in the diagram are for conceptualization only.
;;
;; A gap buffer port is a soft port (see Guile manual) that wraps a gap
;; buffer. Character and string writes, as well as character reads, are
;; supported. Flushing and closing are not supported.
;;
;; These procedures are exported:
;; (gb? OBJ)
;; (make-gap-buffer . INIT)
;; (gb-point GB)
;; (gb-point-min GB)
;; (gb-point-max GB)
;; (gb-insert-string! GB STRING)
;; (gb-insert-char! GB CHAR)
;; (gb-delete-char! GB COUNT)
;; (gb-goto-char GB LOCATION)
;; (gb->string GB)
;; (gb-filter! GB STRING-PROC)
;; (gb->lines GB)
;; (gb-filter-lines! GB LINES-PROC)
;; (make-gap-buffer-port GB)
;;
;; INIT is an optional port or a string. COUNT and LOCATION are integers.
;; STRING-PROC is a procedure that takes and returns a string. LINES-PROC is
;; a procedure that takes and returns a list of strings, each representing a
;; line of text (newlines are stripped and added back automatically).
;;
;; (The term and concept of "gap buffer" are borrowed from Emacs. We will
;; gladly return them when libemacs.so is available. ;-)
;;
;; Notes:
;; - overrun errors are suppressed silently
;;; Code:
(define-module (ice-9 gap-buffer)
#:use-module (srfi srfi-9)
#:export (gb?
make-gap-buffer
gb-point
gb-point-min
gb-point-max
gb-insert-string!
gb-insert-char!
gb-delete-char!
gb-erase!
gb-goto-char
gb->string
gb-filter!
gb->lines
gb-filter-lines!
make-gap-buffer-port))
(define-record-type gap-buffer
(new)
gb?
(s s: s!) ; the buffer, a string
(all-sz all-sz: all-sz!) ; total allocation
(gap-ofs gap-ofs: gap-ofs!) ; GAP starts, aka (1- point)
(aft-ofs aft-ofs: aft-ofs!)) ; AFTER starts
;; todo: expose
(define default-initial-allocation 128)
(define default-chunk-size 128)
(define default-realloc-threshold 32)
(define (round-up n)
(* default-chunk-size (+ 1 (quotient n default-chunk-size))))
(define (realloc gb inc)
(let* ((old-s (s: gb))
(all-sz (all-sz: gb))
(new-sz (+ all-sz inc))
(gap-ofs (gap-ofs: gb))
(aft-ofs (aft-ofs: gb))
(new-s (make-string new-sz))
(new-aft-ofs (+ aft-ofs inc)))
(substring-move! old-s 0 gap-ofs new-s 0)
(substring-move! old-s aft-ofs all-sz new-s new-aft-ofs)
(s! gb new-s)
(all-sz! gb new-sz)
(aft-ofs! gb new-aft-ofs)))
(define (make-gap-buffer . init) ; port/string
(let ((gb (new)))
(cond ((null? init)
(s! gb (make-string default-initial-allocation))
(all-sz! gb default-initial-allocation)
(gap-ofs! gb 0)
(aft-ofs! gb default-initial-allocation))
(else (let ((jam! (lambda (string len)
(let ((alloc (round-up len)))
(s! gb (make-string alloc))
(all-sz! gb alloc)
(substring-move! string 0 len (s: gb) 0)
(gap-ofs! gb len)
(aft-ofs! gb alloc))))
(v (car init)))
(cond ((port? v)
(let ((next (lambda () (read-char v))))
(let loop ((c (next)) (acc '()) (len 0))
(if (eof-object? c)
(jam! (list->string (reverse acc)) len)
(loop (next) (cons c acc) (1+ len))))))
((string? v)
(jam! v (string-length v)))
(else (error "bad init type"))))))
gb))
(define (gb-point gb)
(1+ (gap-ofs: gb)))
(define (gb-point-min gb) 1) ; no narrowing (for now)
(define (gb-point-max gb)
(1+ (- (all-sz: gb) (- (aft-ofs: gb) (gap-ofs: gb)))))
(define (insert-prep gb len)
(let* ((gap-ofs (gap-ofs: gb))
(aft-ofs (aft-ofs: gb))
(slack (- (- aft-ofs gap-ofs) len)))
(and (< slack default-realloc-threshold)
(realloc gb (round-up (- slack))))
gap-ofs))
(define (gb-insert-string! gb string)
(let* ((len (string-length string))
(gap-ofs (insert-prep gb len)))
(substring-move! string 0 len (s: gb) gap-ofs)
(gap-ofs! gb (+ gap-ofs len))))
(define (gb-insert-char! gb char)
(let ((gap-ofs (insert-prep gb 1)))
(string-set! (s: gb) gap-ofs char)
(gap-ofs! gb (+ gap-ofs 1))))
(define (gb-delete-char! gb count)
(cond ((< count 0) ; backwards
(gap-ofs! gb (max 0 (+ (gap-ofs: gb) count))))
((> count 0) ; forwards
(aft-ofs! gb (min (all-sz: gb) (+ (aft-ofs: gb) count))))
((= count 0) ; do nothing
#t)))
(define (gb-erase! gb)
(gap-ofs! gb 0)
(aft-ofs! gb (all-sz: gb)))
(define (point++n! gb n s gap-ofs aft-ofs) ; n>0; warning: reckless
(substring-move! s aft-ofs (+ aft-ofs n) s gap-ofs)
(gap-ofs! gb (+ gap-ofs n))
(aft-ofs! gb (+ aft-ofs n)))
(define (point+-n! gb n s gap-ofs aft-ofs) ; n<0; warning: reckless
(substring-move! s (+ gap-ofs n) gap-ofs s (+ aft-ofs n))
(gap-ofs! gb (+ gap-ofs n))
(aft-ofs! gb (+ aft-ofs n)))
(define (gb-goto-char gb new-point)
(let ((pmax (gb-point-max gb)))
(or (and (< new-point 1) (gb-goto-char gb 1))
(and (> new-point pmax) (gb-goto-char gb pmax))
(let ((delta (- new-point (gb-point gb))))
(or (= delta 0)
((if (< delta 0)
point+-n!
point++n!)
gb delta (s: gb) (gap-ofs: gb) (aft-ofs: gb))))))
new-point)
(define (gb->string gb)
(let ((s (s: gb)))
(string-append (substring s 0 (gap-ofs: gb))
(substring s (aft-ofs: gb)))))
(define (gb-filter! gb string-proc)
(let ((new (string-proc (gb->string gb))))
(gb-erase! gb)
(gb-insert-string! gb new)))
(define (gb->lines gb)
(let ((str (gb->string gb)))
(let loop ((start 0) (acc '()))
(cond ((string-index str #\newline start)
=> (lambda (w)
(loop (1+ w) (cons (substring str start w) acc))))
(else (reverse (cons (substring str start) acc)))))))
(define (gb-filter-lines! gb lines-proc)
(let ((new-lines (lines-proc (gb->lines gb))))
(gb-erase! gb)
(gb-insert-string! gb (string-join new-lines #\newline))))
(define (make-gap-buffer-port gb)
(or (gb? gb)
(error "not a gap-buffer:" gb))
(make-soft-port
(vector
(lambda (c) (gb-insert-char! gb c))
(lambda (s) (gb-insert-string! gb s))
#f
(lambda () (let ((gap-ofs (gap-ofs: gb))
(aft-ofs (aft-ofs: gb)))
(if (= aft-ofs (all-sz: gb))
#f
(let* ((s (s: gb))
(c (string-ref s aft-ofs)))
(string-set! s gap-ofs c)
(gap-ofs! gb (1+ gap-ofs))
(aft-ofs! gb (1+ aft-ofs))
c))))
#f)
"rw"))
;;; gap-buffer.scm ends here
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