scsh-0.5/scsh/rdelim.scm

;;; Delimited readers
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; These procedures run their inner I/O loop in a C primitive, so they
;;; should be quite fast.
;;;
;;; N.B.:
;;; The C primitive %READ-DELIMITED-FDPORT!/ERRNO relies on knowing the
;;; representation of character sets. If these are changed from their
;;; current representation as 256-element strings, this code must be changed
;;; as well. 

;;; (read-delimited delims [port delim-action])
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Returns a string or the EOF object. DELIM-ACTION determines what to do
;;; with the terminating delimiter:
;;; - PEEK
;;;   Leave it in the input stream for later reading.
;;; - TRIM (the default)
;;;   Drop it on the floor.
;;; - CONCAT
;;;   Append it to the returned string.
;;; - SPLIT
;;;   Return it as a second return value.
;;;
;;; We repeatedly allocate a buffer and fill it with READ-DELIMITED!
;;; until we hit a delimiter or EOF. Each time through the loop, we
;;; double the total buffer space, so the loop terminates with a log
;;; number of reads, but uses at most double the optimal buffer space.

(define (read-delimited delims . args)
  (receive (port delim-action)
           (parse-optionals args (current-input-port) 'trim)

    (let ((substr (lambda (s end)		; Smart substring.
		    (if (= end (string-length s)) s
			(substring s 0 end))))
	  (delims (->char-set delims))
	  (gobble? (not (eq? delim-action 'peek))))
	
      ;; BUFLEN is total amount of buffer space allocated to date.
      (let lp ((strs '()) (buflen 80) (buf (make-string 80)))
	(receive (terminator num-read)
	         (%read-delimited! delims buf gobble? port)
	  (if terminator

	      ;; We are done. NUM-READ is either a read count or EOF.
	      (let ((retval (if (and (zero? num-read)
				     (eof-object? terminator)
				     (null? strs))
				terminator		; EOF -- got nothing.

				;; Got something. Stick all the strings
				;; together, plus the terminator if the
				;; client said 'CONCAT.
				(let ((s (substr buf num-read)))
				  (cond ((and (eq? delim-action 'concat)
					      (char? terminator))
					 (apply string-append
						(reverse `(,(string terminator)
							   ,s . ,strs))))

					((null? strs) s)    ; Gratuitous opt.
					(else (apply string-append
						     (reverse (cons s strs)))))))))
		(if (eq? delim-action 'split)
		    (values retval terminator)
		    retval))

	      ;; We are not done. Loop and read in some more.
	      (lp (cons buf strs)
		  (+ buflen buflen)
		  (make-string buflen))))))))


;;; (read-delimited! delims buf [port delim-action start end])
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Returns:
;;; - EOF if at end of file, and a non-zero read was requested.
;;; - Integer j if that many chars read into BUF.
;;; - #f if the buffer was filled w/o finding a delimiter.
;;;
;;; DELIM-ACTION determines what to do with the terminating delimiter;
;;; it is as in READ-DELIMITED.
;;;
;;; In determining the return value, there is an ambiguous case: when the 
;;; buffer is full, *and* the following char is a delimiter char or EOF.
;;; Ties are broken favoring termination over #f -- after filling the buffer,
;;; READ-DELIMITED! won't return #f until it has peeked one past the end
;;; of the buffer to ensure the next char doesn't terminate input (or is EOF).
;;; However, this rule is relaxed with delim-action = CONCAT -- if the buffer
;;; is full, READ-DELIMITED! won't wait around trying to peek at the following
;;; char to determine whether or not it is a delimiter char, since it doesn't
;;; have space to store the character anyway. It simply immediately returns #f;
;;; a following read can pick up the delimiter char.

(define (read-delimited! delims buf . args) ; [port delim-action start end]
  (receive (port delim-action start end)
           (parse-optionals args (current-input-port) 'peek
			    0 (string-length buf))

    (receive (terminator num-read)
	     (%read-delimited! delims buf
			       (not (eq? delim-action 'peek)) ;Gobble delim?
			       port
			       start
			       (if (eq? delim-action 'concat)
				   (- end 1) ; Room for terminator.
				   end))

      (if terminator	; Check for buffer overflow.
	  (let ((retval (if (and (eof-object? terminator)
				 (zero? num-read))
			    terminator	; EOF -- got nothing.
			    num-read))) ; Got something.

	    (case delim-action
	      ((split)	(values retval terminator))
	      ((peek trim)	retval)
	      ((concat)	(cond ((char? terminator)
			       (string-set! buf (+ start num-read) terminator)
			       (+ num-read 1))
			      (else retval)))))

	  ;; Buffer overflow.
	  (case delim-action
	    ((split)     (values #f #f))
	    ((peek trim) #f)
	    ((concat)    (let ((last (read-char port)))
			   (if (char? last)
			       (string-set! buf (+ start num-read) last))
			   (and (or (eof-object? last)
				    (char-set-contains? (->char-set delims)
							last))
				(+ num-read 1)))))))))
		  

;;; (%read-delimited! delims buf gobble? [port start end])
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; This low-level routine uses a different interface. It returns two values:
;;; - TERMINATOR: A value describing why the read was terminated:
;;;   + character or eof-object => read terminated by this value; 
;;;   + #f                      => filled buffer w/o terminating read.
;;; - NUM-READ: Number of chars read into buf.
;;; 
;;; Note:
;;; - Invariant: TERMINATOR = #f  =>  NUM-READ = END - START.
;;; - Invariant: TERMINATOR = eof-object and NUM-READ = 0 => at EOF.
;;; - When determining the TERMINATOR return value, ties are broken
;;;   favoring character or the eof-object over #f. That is, if the buffer
;;;   fills up, %READ-DELIMITED! will peek at one more character from the
;;;   input stream to determine if it terminates the input. If so, that
;;;   is returned, not #f.
;;;
;;; If GOBBLE? is true, then a terminator character is removed from
;;; the input stream. Otherwise, it is left in place for a following input
;;; operation.

(define (%read-delimited! delims buf gobble? . args)
  (receive (port start end)
	   (parse-optionals args (current-input-port) 0 (string-length buf))

    (check-arg input-port? port %read-delimited!)	; Arg checking.
    (check-arg char-set? delims %read-delimited!)	; Required, since
    (if (bogus-substring-spec? buf start end)		; we're calling C.
	(error "Illegal START/END substring indices"
	       buf start end %read-delimited!))

    (let ((delims (->char-set delims)))

      (if (fdport? port)

	  ;; Direct C support for Unix file ports -- zippy quick.
	  (receive (terminator num-read)
	           (%read-delimited-fdport!/errno delims buf gobble?
						  port start end)
	    (if (integer? terminator)
		(errno-error terminator %read-delimited! num-read
			     delims buf gobble? port start end)
		(values terminator num-read)))

	  ;; This is the code for other kinds of ports.
	  ;; Mighty slow -- we read each char twice (peek first, then read).
	  (let lp ((i start))
	    (let ((c (peek-char port)))
	      (cond ((or (eof-object? c)	; Found terminating char or eof
			 (char-set-contains? delims c))
		     (if gobble? (read-char port))
		     (values c (- i start)))

		    ((>= i end)			; Filled the buffer.
		     (if gobble? (read-char port))
		     (values #f (- i start)))
			
		    (else (string-set! buf i (read-char port))
			  (lp (+ i 1))))))))))


(foreign-source
  "#include <sys/types.h>"
  ""
  "/* Make sure foreign-function stubs interface to the C funs correctly: */"
  "#include \"fdports1.h\""
  "" "")

(define-foreign %read-delimited-fdport!/errno (read_delim (string delims)
							  (var-string buf)
							  (bool gobble?)
							  (desc port)
							  (fixnum start)
							  (fixnum end))
  desc	; int => errno; char => terminating char; eof-object; #f => buf ovflow
  fixnum)   ; number of chars read into BUF.


;;; This is probably a hell of lot slower than actually reading the string
;;; into a buffer and throwing it away, due to the painful slowness of
;;; the current char-at-a-time Scheme input.

(define (skip-char-set cset . maybe-port)
  (let ((port (optional-arg maybe-port (current-input-port))))
    (let lp ()
      (let ((c (peek-char port)))
	(cond ((and (char? c) (char-set-contains? cset c))
	       (read-char port)
	       (lp))
	      (else c))))))


;;; (read-line [port delim-action])
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Read in a line of data. Input is terminated by either a newline or EOF.
;;; The newline is trimmed from the string by default.

(define charset:newline (char-set #\newline))

(define (read-line . rest)
  (receive (port delim-action)
           (parse-optionals rest (current-input-port) 'trim)
    (read-delimited charset:newline port delim-action)))


;;; (read-paragraph [port handle-delim])
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(define blank-line-regexp (make-regexp "^[ \t]*\n$"))

(define (read-paragraph . args)
  (receive (port handle-delim)
           (parse-optionals args (current-input-port) 'trim)
    
    ;; First, skip all blank lines.
    (let lp ()
      (let ((line (read-line port 'concat)))
	(cond ((eof-object? line)
	       (if (eq? handle-delim 'split) (values line line) line))

	      ((regexp-exec blank-line-regexp line) (lp))

	      ;; Then, read in non-blank lines.
	      (else
	       (let lp ((lines (list line)))
		 (let ((line (read-line port 'concat)))
		   (if (and (string? line)
			    (not (regexp-exec blank-line-regexp line)))

		       (lp (cons line lines))

		       ;; Return the paragraph
		       (let ((->str (lambda (lns) (apply string-append (reverse lns)))))
			 (case handle-delim
			   ((trim) (->str lines))

			   ((concat)
			    (->str (if (eof-object? line) lines (cons line lines))))

			   ((split)
			    (values (->str lines) line))

			   (else (error "Illegal HANDLE-DELIM parameter to READ-PARAGRAPH")))))))))))))