; -*- Mode: Scheme; Syntax: Scheme; Package: Scheme; -*-
; Copyright (c) 1993-1999 by Richard Kelsey and Jonathan Rees. See file COPYING.


; A little Scheme reader.

; Nonstandard things used:
;  Ascii stuff: char->ascii, ascii->char, ascii-whitespaces, ascii-limit
;    (for dispatch table; portable definitions in alt/ascii.scm)
;  reverse-list->string  -- ok to define as follows:
;    (define (reverse-list->string l n)
;      (list->string (reverse l)))
;  make-immutable! -- ok to define as follows:
;    (define (make-immutable! x) x)
;  signal (only for use by reading-error; easily excised)

;scsh start

(define preferred-case (lambda (x) x))

(define (script-skip c port)
  (read-char port)
    (let lp ((state 0))
      (let ((advance-if (lambda (look-for)
			  (let ((c (read-char port)))
			    (if (eof-object? c)
				(reading-error  port
			 "EOF inside block comment -- #! missing a closing !#")
				(lp (cond ((char=? c look-for) (+ state 1))
					  ((char=? c #\newline) 1)
					  ((char=? c cr) state)
					  (else 0))))))))
	(case state
	  ((0) (advance-if #\newline))
	  ((1) (advance-if #\!))	; Found \n
	  ((2) (advance-if #\#))	; Found \n!
	  ((3) (advance-if #\newline))	; Found \n!#
	  ((4) (read port))
	  (else 
	   (reading-error port "case other"))))))	; Found \n!#\n -- done.
;         was sub-read ^


(define (multi-line-comment-skip c port)
  (read-char port)
  (let lp ((state 0) (nested? #f))
    (let* ((advance-one-of-two 
	    (lambda (look-for1 state1 look-for2 state2 nested?)
			  (let ((c (read-char port)))
			    (if (eof-object? c)
				(error 
			 "EOF inside block comment -- #| missing a closing |#")
				(lp (cond ((char=? c look-for1) state1)
					  ((char=? c look-for2) state2)
					  (else 0)) nested?)))))
	   (advance-if (lambda (look-for state nested?)
			 (advance-one-of-two look-for state 
					     look-for state 
					     nested?))))
      (case state
	((0) (advance-one-of-two #\| 1 #\# 5 nested?))
	((1) (advance-if #\# 2 nested?))
	((2) (if nested? #f (sub-read port)))
	((5) (advance-if #\| 6 nested?))
	((6) (lp 0 #t) (lp 0 nested?))))))
    

; scsh stop

(define (read . port-option)
  (let ((port (input-port-option port-option)))
    (let loop ()
      (let ((form (sub-read port)))
        (cond ((not (reader-token? form)) form)
              ((eq? form close-paren)
               ;; Too many right parens.
	       (warn "discarding extraneous right parenthesis")
               (loop))
	      (else
	       (reading-error port (cdr form))))))))

(define (sub-read-carefully port)
  (let ((form (sub-read port)))
    (cond ((eof-object? form)
           (reading-error port "unexpected end of file"))
	  ((reader-token? form) (reading-error port (cdr form)))
	  (else form))))

(define reader-token-marker (list 'reader-token))
(define (make-reader-token message) (cons reader-token-marker message))
(define (reader-token? form)
  (and (pair? form) (eq? (car form) reader-token-marker)))

(define close-paren (make-reader-token "unexpected right parenthesis"))
(define dot         (make-reader-token "unexpected \" . \""))


; Main dispatch

(define (sub-read port)
  (let ((c (read-char port)))
    (if (eof-object? c)
        c
        ((vector-ref read-dispatch-vector (char->ascii c))
         c port))))

(define read-dispatch-vector
  (make-vector ascii-limit
               (lambda (c port)
                 (reading-error port "illegal character read" c))))

(define read-terminating?-vector
  (make-vector ascii-limit #t))

(define (set-standard-syntax! char terminating? reader)
  (vector-set! read-dispatch-vector     (char->ascii char) reader)
  (vector-set! read-terminating?-vector (char->ascii char) terminating?))

(let ((sub-read-whitespace
       (lambda (c port)
         c                              ;ignored
         (sub-read port))))
  (for-each (lambda (c)
              (vector-set! read-dispatch-vector c sub-read-whitespace))
            ascii-whitespaces))

(let ((sub-read-constituent
       (lambda (c port)
	 (parse-token (sub-read-token c port) port))))
  (for-each (lambda (c)
              (set-standard-syntax! c #f sub-read-constituent))
            (string->list
             (string-append "!$%&*+-./0123456789:<=>?@^_~ABCDEFGHIJKLM"
                            "NOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"))))

; Usual read macros

(define (set-standard-read-macro! c terminating? proc)
  (set-standard-syntax! c terminating? proc))

(define (sub-read-list c port)
  (let ((form (sub-read port)))
    (if (eq? form dot)
	(reading-error port
		       "missing car -- ( immediately followed by .")
	(let recur ((form form))
	  (cond ((eof-object? form)
		 (reading-error port
				"end of file inside list -- unbalanced parentheses"))
		((eq? form close-paren) '())
		((eq? form dot)
		 (let* ((last-form (sub-read-carefully port))
			(another-form (sub-read port)))
		   (if (eq? another-form close-paren)
		       last-form
		       (reading-error port
				      "randomness after form after dot"
				      another-form))))
		(else
		 (cons form (recur (sub-read port)))))))))

(set-standard-read-macro! #\( #t sub-read-list)

(set-standard-read-macro! #\) #t
  (lambda (c port)
    c port
    close-paren))

(set-standard-read-macro! #\' #t
  (lambda (c port)
    c
    (list 'quote (sub-read-carefully port))))

(set-standard-read-macro! #\` #t
  (lambda (c port)
    c
    (list 'quasiquote (sub-read-carefully port))))

(set-standard-read-macro! #\, #t
  (lambda (c port)
    c
    (let* ((next (peek-char port))
	   ;; DO NOT beta-reduce!
	   (keyword (cond ((eof-object? next)
			   (reading-error port "end of file after ,"))
			  ((char=? next #\@)
			   (read-char port)
			   'unquote-splicing)
			  (else 'unquote))))
      (list keyword
            (sub-read-carefully port)))))

;(set-standard-read-macro! #\" #t
;  (lambda (c port)
;    c ;ignored
;    (let loop ((l '()) (i 0))
;      (let ((c (read-char port)))
;        (cond ((eof-object? c)
;               (reading-error port "end of file within a string"))
;              ((char=? c #\\)
;               (let ((c (read-char port)))
;		 (cond ((eof-object? c)
;			(reading-error port "end of file within a string"))
;		       ((or (char=? c #\\) (char=? c #\"))
;			(loop (cons c l) (+ i 1)))
;		       (else
;			(reading-error port
;				       "invalid escaped character in string"
;				       c)))))
;              ((char=? c #\")
;	       (reverse-list->string l i))
;              (else
;	       (loop (cons c l) (+ i 1))))))))

(set-standard-read-macro! #\; #t
  (lambda (c port)
    c ;ignored
    (gobble-line port)
    (sub-read port)))

(define (gobble-line port)
  (let loop ()
    (let ((c (read-char port)))
      (cond ((eof-object? c) c)
	    ((char=? c #\newline) #f)
	    (else (loop))))))

(define *sharp-macros* '())

(define (define-sharp-macro c proc)
  (set! *sharp-macros* (cons (cons c proc) *sharp-macros*)))

(set-standard-read-macro! #\# #f
  (lambda (c port)
    c ;ignored
    (let* ((c (peek-char port))
	   (c (if (eof-object? c)
		  (reading-error port "end of file after #")
		  (char-downcase c)))
	   (probe (assq c *sharp-macros*)))
      (if probe
	  ((cdr probe) c port)
	  (reading-error port "unknown # syntax" c)))))

(define-sharp-macro #\f
  (lambda (c port) (read-char port) #f))

(define-sharp-macro #\t
  (lambda (c port) (read-char port) #t))

(define-sharp-macro #\\
  (lambda (c port)
    (read-char port)
    (let ((c (peek-char port)))
      (cond ((eof-object? c)
	     (reading-error port "end of file after #\\"))
	    ((char-alphabetic? c)
	     (let ((name (sub-read-carefully port)))
	       (cond ((= (string-length (symbol->string name)) 1)
		      c)
		     ((assq name '((space   #\space)
				   (newline #\newline)))
		      => cadr)
		     (else
		      (reading-error port "unknown #\\ name" name)))))
	    (else
	     (read-char port)
	     c)))))

(define-sharp-macro #\(
  (lambda (c port)
    (read-char port)
    (list->vector (sub-read-list c port))))

(let ((number-sharp-macro
       (lambda (c port)
	 (let ((string (sub-read-token #\# port)))
	   (or (string->number string)
	       (reading-error port "unsupported number syntax" string))))))
  (for-each (lambda (c)
	      (define-sharp-macro c number-sharp-macro))
	    '(#\b #\o #\d #\x #\i #\e)))

(define-sharp-macro #\! script-skip)

(define-sharp-macro #\| multi-line-comment-skip)

; Tokens

(define (sub-read-token c port)
  (let loop ((l (list (preferred-case c))) (n 1))
    (let ((c (peek-char port)))
      (cond ((or (eof-object? c)
                 (vector-ref read-terminating?-vector (char->ascii c)))
             (reverse-list->string l n))
            (else
	     (read-char port)
             (loop (cons (preferred-case c) l)
                   (+ n 1)))))))

;(define (parse-token string port)
;  (if (let ((c (string-ref string 0)))
;	(or (char-numeric? c) (char=? c #\+) (char=? c #\-) (char=? c #\.)))
;      (cond ((string->number string))
;	    ((member string strange-symbol-names)
;	     (string->symbol (make-immutable! string)))
;	    ((string=? string ".")
;	     dot)
;	    (else
;	     (reading-error port "unsupported number syntax" string)))
;      (string->symbol (make-immutable! string))))

; scsh start
(define (parse-token string port)
  (if (let ((c (string-ref string 0)))
	(or (char-numeric? c) (char=? c #\+) (char=? c #\-) (char=? c #\.)))
      (cond ((string->number string))
	    ((string=? string ".") dot)
	    (else (string->symbol (make-immutable! string))))
      (string->symbol (make-immutable! string))))

(set-standard-syntax! #\| #f
		      (lambda (c port)
			(parse-token (sub-read-token c port) port)))



(define bel (ascii->char 7))
(define bs  (ascii->char  8))
(define ff  (ascii->char 12))
(define cr  (ascii->char 13))
(define ht  (ascii->char  9))
(define vt  (ascii->char 11))

;;; Full ANSI C strings:
;;; - read as themselves: \\ \? \" \'
;;; - control chars:
;;;   \a alert (bell -- ^g)
;;;   \b backspace (^h)
;;;   \f form feed (^l)
;;;   \n newline (^j)
;;;   \r carriage return (^m)
;;;   \t tab (^i)
;;;   \v vertical tab (^k)
;;; - octal escapes \nnn
;;; - hex escapes \xnn

;;; Is this the elegant thing to do? Too much might make it hard to shift
;;; to Unicode implementations. How about \^g for embedding control chars?
;;; And I haven't done anything about chars (as opposed to strings).

(set-standard-read-macro! #\" #t
  (lambda (c port)
    c ;ignored
    (let* ((readc (lambda ()
		    (let ((c (read-char port)))
		      (if (eof-object? c)
			  (reading-error port "end of file within a string")
			  c))))
	   (read-digit (lambda (base base-name)
			 (let* ((c (readc))
				(d (- (char->ascii c) (char->ascii #\0))))
			   (if (and (<= 0 d) (< d base)) d
			       (reading-error port
					      (string-append "invalid "
							     base-name
							     " code in string.")
					      d))))))

      (let loop ((l '()) (i 0))
	(let ((c (readc)))
	  (cond ((char=? c #\\)
		 (let* ((c (readc))
			(rc (case c
			      ((#\\ #\" #\? #\') c)
			      ((#\a) bel)
			      ((#\b) bs)
			      ((#\f) ff)
			      ((#\n) #\newline)
			      ((#\r) cr)
			      ((#\t) ht)
			      ((#\v) vt)
			      ((#\0 #\1 #\2 #\3)
			       (let* ((d1 (- (char->ascii c) (char->ascii #\0)))
				      (d2 (read-digit 8 "octal"))
				      (d3 (read-digit 8 "octal")))
				 (ascii->char (+ (* 64 d1) (+ (* 8 d2) d3)))))
			      ((#\x)
			       (let ((d1 (read-digit 16 "hex"))
				     (d2 (read-digit 16 "hex")))
				 (ascii->char (+ (* 16 d1) d2))))
			      (else
			       (reading-error port
					      "invalid escapedcharacter in string"
					      c)))))
		   (loop (cons rc l) (+ i 1))))
		((char=? c #\")
		 (reverse-list->string l i))
		(else
		 (loop (cons c l) (+ i 1)))))))))

;scsh stop

(define strange-symbol-names
  '("+" "-" "..."
	"1+" "-1+"  ;Only for S&ICP support
	"->"	    ;Only for JAR's thesis
	))

;--- This loses because the compiler won't in-line it.  Hacked by hand
; because it is in READ's inner loop.
;(define preferred-case
;  (if (char=? (string-ref (symbol->string 't) 0) #\T)
;      char-upcase
;      char-downcase))

(define p-c-v (make-string ascii-limit #\0))

(let ((p-c (if (char=? (string-ref (symbol->string 't) 0) #\T)
	       char-upcase
	       char-downcase)))
  (do ((i 0 (+ i 1)))
      ((>= i ascii-limit))
    (string-set! p-c-v i (p-c (ascii->char i)))))

;(define (preferred-case c)
;  (string-ref p-c-v (char->ascii c)))

; Reader errors

(define (reading-error port message . irritants)
  (apply signal 'read-error message
	 (append irritants (list port))))