ice-9/lineio.scm

   1 ;;; installed-scm-file
   2
   3 ;;;;    Copyright (C) 1996 Free Software Foundation, Inc.
   4 ;;;;
   5 ;;;; This program is free software; you can redistribute it and/or modify
   6 ;;;; it under the terms of the GNU General Public License as published by
   7 ;;;; the Free Software Foundation; either version 2, or (at your option)
   8 ;;;; any later version.
   9 ;;;;
  10 ;;;; This program is distributed in the hope that it will be useful,
  11 ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 ;;;; GNU General Public License for more details.
  14 ;;;;
  15 ;;;; You should have received a copy of the GNU General Public License
  16 ;;;; along with this software; see the file COPYING.  If not, write to
  17 ;;;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  18 ;;;;
  19
  20 \f
  21
  22 (define-module #/ice-9/lineio)
  23
  24 \f
  25 ;;; {Line Buffering Input Ports}
  26 ;;;
  27 ;;; [This is a work-around to get past certain deficiencies in the capabilities
  28 ;;;  of ports.  Eventually, ports should be fixed and this module nuked.]
  29 ;;;
  30 ;;; A line buffering input port supports:
  31 ;;;
  32 ;;;     read-string     which returns the next line of input
  33 ;;;     unread-string   which pushes a line back onto the stream
  34 ;;;
  35 ;;; Normally a "line" is all characters up to and including a newline.
  36 ;;; If lines are put back using unread-string, they can be broken arbitrarily
  37 ;;; -- that is, read-string returns strings passed to unread-string (or
  38 ;;; shared substrings of them).
  39 ;;;
  40
  41 ;; read-string port
  42 ;; unread-string port str
  43 ;;   Read (or buffer) a line from PORT.
  44 ;;
  45 ;; Not all ports support these functions -- only those with
  46 ;; 'unread-string and 'read-string properties, bound to hooks
  47 ;; implementing these functions.
  48 ;;
  49 (define-public (unread-string str line-buffering-input-port)
  50   ((object-property line-buffering-input-port 'unread-string) str))
  51
  52 ;;
  53 (define-public (read-string line-buffering-input-port)
  54   ((object-property line-buffering-input-port 'read-string)))
  55
  56
  57 (define-public (lineio-port? port)
  58   (not (not (object-property port 'read-string))))
  59
  60 ;; make-line-buffering-input-port port
  61 ;;   Return a wrapper for PORT.  The wrapper handles read-string/unread-string.
  62 ;;
  63 ;; The port returned by this function reads newline terminated lines from PORT.
  64 ;; It buffers these characters internally, and parsels them out via calls
  65 ;; to read-char, read-string, and unread-string.
  66 ;;
  67
  68 (define-public (make-line-buffering-input-port underlying-port)
  69   (let* (;; buffers - a list of strings put back by unread-string or cached
  70          ;; using read-line.
  71          ;;
  72          (buffers '())
  73
  74          ;; getc - return the next character from a buffer or from the underlying
  75          ;; port.
  76          ;;
  77          (getc (lambda ()
  78                  (if (not buffers)
  79                      (read-char underlying-port)
  80                      (let ((c (string-ref (car buffers))))
  81                        (if (= 1 (string-length (car buffers)))
  82                            (set! buffers (cdr buffers))
  83                            (set-car! buffers (make-shared-substring (car buffers) 1)))
  84                        c))))
  85
  86          (propogate-close (lambda () (close-port underlying-port)))
  87
  88          (self (make-soft-port (vector #f #f #f getc propogate-close) "r"))
  89
  90          (unread-string (lambda (str)
  91                           (and (< 0 (string-length str))
  92                                (if (ungetc-char-ready? self)
  93                                    (set! buffers (append! (list str (string (read-char self))) buffers))
  94                                    (set! buffers (cons str buffers))))))
  95
  96          (read-string (lambda ()
  97                        (cond
  98                         ((not (null? buffers))
  99                          (let ((answer (car buffers)))
 100                            (set! buffers (cdr buffers))
 101                            answer))
 102                         ((ungetc-char-ready? self)
 103                          (read-line self 'include-newline))
 104                         (else
 105                          (read-line underlying-port 'include-newline))))))
 106
 107     (set-object-property! self 'unread-string unread-string)
 108     (set-object-property! self 'read-string read-string)
 109     self))
 110
 111