scsh-0.5/scsh/meta-arg.scm

135 lines
4.8 KiB
Scheme

;;; Meta-arg argv processor in Scheme.
;;; Copyright (c) 1995 by Olin Shivers.
;;;
;;; This is a Scheme analog of the proc2.c meta-arg expander.
;;; Syntax of the line 2 argument line:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; - The only special chars are space, tab, newline, and \.
;;; - Every space char terminates an argument.
;;; Multiple spaces therefore introduce empty-string arguments.
;;; - A newline terminates the argument list, and will also terminate a
;;; non-empty argument (but a newline following a space does not introduce
;;; a final "" argument; it only terminates the argument list).
;;; - Tab is not allowed.
;;; This is to prevent you from being screwed by thinking you had several
;;; spaces where you really had a tab, and vice-versa.
;;; - The only other special character is \, the knock-down character.
;;; \ escapes \, space, tab, and newline, turning off their special
;;; functions. The ANSI C escapes sequences, such as \n and \t are
;;; supported; these also produce argument-constituents -- \n doesn't act
;;; like a terminating newline. \nnn for *exactly* three octal digits reads
;;; as the char whose ASCII code is nnn. It is an error if \ is followed by
;;; just 1 or 2 octal digits: \3Q is an error. Octal-escapes are always
;;; constituent chars. \ followed by other chars is not allowed (so we can
;;; extend the escape-code space later if we like).
;;;
;;; You have to construct these line-2 arg lines carefully. For example,
;;; beware of trailing spaces at the end of the line. They'll give you
;;; extra trailing empty-string args.
;;; (meta-arg-process-arglist args)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Expand out meta-args in argument lists.
;;;
;;; ARGS is an argument list -- a list of strings. If the first two elements
;;; are of the form ("\\" <filename> ...), then parse secondary arguments
;;; from line two of file <filename>, change the argument list to
;;; (,@<secondary-args> <filename> ...)
;;; and loop.
(define (meta-arg-process-arglist args)
(let lp ((args args))
(if (and (pair? args)
(string=? (car args) "\\"))
(lp (append (read-files-secondary-args (cadr args))
(cdr args)))
args)))
;;; (read-files-secondary-args fname)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Open file FNAME, skip the first line, and read secondary args off of
;;; line two. Return these as a list of strings.
(define read-files-secondary-args
(let ((non-newline (char-set-invert (char-set #\newline))))
(lambda (fname)
(call-with-input-file fname
(lambda (port)
(skip-char-set non-newline port) ; Skip the first
(read-char port) ; line of text.
(read-secondary-args port))))))
;;; Read in a line of secondary args from PORT.
(define (read-secondary-args port)
(let lp ((args '()))
(let ((c (peek-char port)))
(if (or (eof-object? c) (char=? c #\newline))
(reverse args)
(lp (cons (read-secondary-arg port) args))))))
;;; Read in one secondary arg.
(define (read-secondary-arg port)
(let lp ((chars '()))
(let ((c (peek-char port)))
(cond ((or (eof-object? c) (char=? c #\newline))
(apply string (reverse chars)))
((char=? c #\space)
(read-char port)
(apply string (reverse chars)))
((char=? c tab)
(error "Illegal tab character in meta-arg argument line."))
(else (lp (cons ((cond ((char=? c #\\)
(read-char port)
read-backslash-sequence)
(else read-char))
port)
chars)))))))
(define (read-backslash-sequence port)
(let ((c1 (read-char port))
(eof-lose (lambda () (error "Premature EOF within backslash-sequence in meta-arg argument line"))))
(cond ((eof-object? c1) (eof-lose))
;; This would be better handled by a char-map abstraction.
((char=? c1 #\n) #\newline)
((char=? c1 #\r) carriage-return)
((char=? c1 #\t) tab)
((char=? c1 #\b) backspace)
;; ...whatever. Look up complete table.
;; \, space, tab, newline.
((char-set-contains? char-set:simple-knockdown c1) c1)
((char-set-contains? char-set:octal-digits c1)
(let ((c2 (read-char port)))
(if (eof-object? c2) (eof-lose)
(let ((c3 (read-char port)))
(if (eof-object? c3) (eof-lose)
(ascii->char (+ (octet->int c3)
(* 8 (+ (octet->int c2)
(* 8 (octet->int c1)))))))))))
(else (error "Illegal \\ escape sequence in meta-arg argument line."
c1)))))
(define (octet->int c) (- (char->ascii c) (char->ascii #\0)))
(define char-set:octal-digits (char-set #\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7))
(define char-set:simple-knockdown (string->char-set "\\ \n\t"))
;;; Yechh.
(define tab (ascii->char 9))
(define carriage-return (ascii->char 13))
(define backspace (ascii->char 8))