-
-;;; In the interest of ``once and only once'' this macro contains the
-;;; framework necessary to implement a peek-char function, which has
-;;; two special-cases (one for gray streams and one for echo streams)
-;;; in addition to the normal case.
-;;;
-;;; All arguments are forms which will be used for a specific purpose
-;;; PEEK-TYPE - the current peek-type as defined by ANSI CL
-;;; EOF-VALUE - the eof-value argument to peek-char
-;;; CHAR-VAR - the variable which will be used to store the current character
-;;; READ-FORM - the form which will be used to read a character
-;;; UNREAD-FORM - ditto for unread-char
-;;; SKIPPED-CHAR-FORM - the form to execute when skipping a character
-;;; EOF-DETECTED-FORM - the form to execute when EOF has been detected
-;;; (this will default to CHAR-VAR)
-(defmacro generalized-peeking-mechanism (peek-type eof-value char-var read-form unread-form &optional (skipped-char-form nil) (eof-detected-form nil))
- `(let ((,char-var ,read-form))
- (cond ((eql ,char-var ,eof-value)
- ,(if eof-detected-form
- eof-detected-form
- char-var))
- ((characterp ,peek-type)
- (do ((,char-var ,char-var ,read-form))
- ((or (eql ,char-var ,eof-value)
- (char= ,char-var ,peek-type))
- (cond ((eql ,char-var ,eof-value)
- ,(if eof-detected-form
- eof-detected-form
- char-var))
- (t ,unread-form
- ,char-var)))
- ,skipped-char-form))
- ((eql ,peek-type t)
- (do ((,char-var ,char-var ,read-form))
- ((or (eql ,char-var ,eof-value)
- (not (whitespace-char-p ,char-var)))
- (cond ((eql ,char-var ,eof-value)
- ,(if eof-detected-form
- eof-detected-form
- char-var))
- (t ,unread-form
- ,char-var)))
- ,skipped-char-form))
- ((null ,peek-type)
- ,unread-form
- ,char-var)
- (t
- (bug "Impossible case reached in PEEK-CHAR")))))
-
-(defun peek-char (&optional (peek-type nil)
- (stream *standard-input*)
- (eof-error-p t)
- eof-value
- recursive-p)
- (declare (ignore recursive-p))
- (the (or character boolean) peek-type)
- (let ((stream (in-synonym-of stream)))
- (cond ((typep stream 'echo-stream)
- (echo-misc stream
- :peek-char
- peek-type
- (list eof-error-p eof-value)))
- ((ansi-stream-p stream)
- (generalized-peeking-mechanism
- peek-type eof-value char
- (read-char stream eof-error-p eof-value)
- (unread-char char stream)))
- (t
- ;; by elimination, must be Gray streams FUNDAMENTAL-STREAM
- (generalized-peeking-mechanism
- peek-type :eof char
- (if (null peek-type)
- (stream-peek-char stream)
- (stream-read-char stream))
- (if (null peek-type)
- ()
- (stream-unread-char stream char))
- ()
- (eof-or-lose stream eof-error-p eof-value))))))