ice-9/lineio.scm

   1 ;;; installed-scm-file
   2
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  44
  45 \f
  46
  47 (define-module (ice-9 lineio)
  48   :use-module (ice-9 readline)
  49   :export (unread-string read-string lineio-port?
  50            make-line-buffering-input-port))
  51
  52 \f
  53 ;;; {Line Buffering Input Ports}
  54 ;;;
  55 ;;; [This is a work-around to get past certain deficiencies in the capabilities
  56 ;;;  of ports.  Eventually, ports should be fixed and this module nuked.]
  57 ;;;
  58 ;;; A line buffering input port supports:
  59 ;;;
  60 ;;;     read-string     which returns the next line of input
  61 ;;;     unread-string   which pushes a line back onto the stream
  62 ;;;
  63 ;;; The implementation of unread-string is kind of limited; it doesn't
  64 ;;; interact properly with unread-char, or any of the other port
  65 ;;; reading functions.  Only read-string will get you back the things that
  66 ;;; unread-string accepts.
  67 ;;;
  68 ;;; Normally a "line" is all characters up to and including a newline.
  69 ;;; If lines are put back using unread-string, they can be broken arbitrarily
  70 ;;; -- that is, read-string returns strings passed to unread-string (or
  71 ;;; shared substrings of them).
  72 ;;;
  73
  74 ;; read-string port
  75 ;; unread-string port str
  76 ;;   Read (or buffer) a line from PORT.
  77 ;;
  78 ;; Not all ports support these functions -- only those with
  79 ;; 'unread-string and 'read-string properties, bound to hooks
  80 ;; implementing these functions.
  81 ;;
  82 (define (unread-string str line-buffering-input-port)
  83   ((object-property line-buffering-input-port 'unread-string) str))
  84
  85 ;;
  86 (define (read-string line-buffering-input-port)
  87   ((object-property line-buffering-input-port 'read-string)))
  88
  89
  90 (define (lineio-port? port)
  91   (not (not (object-property port 'read-string))))
  92
  93 ;; make-line-buffering-input-port port
  94 ;;   Return a wrapper for PORT.  The wrapper handles read-string/unread-string.
  95 ;;
  96 ;; The port returned by this function reads newline terminated lines from PORT.
  97 ;; It buffers these characters internally, and parsels them out via calls
  98 ;; to read-char, read-string, and unread-string.
  99 ;;
 100
 101 (define (make-line-buffering-input-port underlying-port)
 102   (let* (;; buffers - a list of strings put back by unread-string or cached
 103          ;; using read-line.
 104          ;;
 105          (buffers '())
 106
 107          ;; getc - return the next character from a buffer or from the underlying
 108          ;; port.
 109          ;;
 110          (getc (lambda ()
 111                  (if (not buffers)
 112                      (read-char underlying-port)
 113                      (let ((c (string-ref (car buffers))))
 114                        (if (= 1 (string-length (car buffers)))
 115                            (set! buffers (cdr buffers))
 116                            (set-car! buffers (substring (car buffers) 1)))
 117                        c))))
 118
 119          (propogate-close (lambda () (close-port underlying-port)))
 120
 121          (self (make-soft-port (vector #f #f #f getc propogate-close) "r"))
 122
 123          (unread-string (lambda (str)
 124                           (and (< 0 (string-length str))
 125                                    (set! buffers (cons str buffers)))))
 126
 127          (read-string (lambda ()
 128                        (cond
 129                         ((not (null? buffers))
 130                          (let ((answer (car buffers)))
 131                            (set! buffers (cdr buffers))
 132                            answer))
 133                         (else
 134                          (read-line underlying-port 'concat)))))) ;handle-newline->concat
 135
 136     (set-object-property! self 'unread-string unread-string)
 137     (set-object-property! self 'read-string read-string)
 138     self))
 139
 140