120 lines
4.4 KiB
Scheme
120 lines
4.4 KiB
Scheme
;;; Here documents in Scheme for scsh scripts.
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;;; These are like "here documents" for sh and csh shell scripts
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;;; (i.e., the <<EOF redirection).
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;;; Copyright (c) 1995 by Olin Shivers. See file COPYING.
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;;; There are two kinds of here string, both introduced by the #< read macro.
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;;;
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;;; Character-delimited here strings:
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;;; A *character-delimited* here string has the form
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;;; #<x...stuff...x
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;;; where x is any single character (except <, see below), which is used
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;;; to delimit the string bounds.
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;;; Here are some examples:
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;;;
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;;; Here string syntax Ordinary syntax
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;;; ------------------ ---------------
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;;; #<|Hello, world.| "Hello, world."
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;;; #<!"Ouch," he said.! "\"Ouch,\" he said."
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;;;
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;;; There is *no* interpretation of characters within the here string;
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;;; characters are all copied verbatim.
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;;;
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;;; Line-delimited here strings:
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;;; If the macro begins "#<<" then it introduces a *line-delimited* here
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;;; string. These are similar to the "here documents" of sh and
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;;; csh. Line-delimited here strings are delimited by the line of text coming
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;;; after the "#<<" sequence. For example:
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;;;
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;;; #<FOO
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;;; Hello, there.
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;;; This is read by Scheme as a string,
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;;; terminated by the first occurrence
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;;; of newline-F-O-O-newline or newline-F-O-O-eof.
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;;; FOO
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;;;
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;;; Thus,
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;;; #<foo
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;;; Hello, world.
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;;; foo
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;;; is the same thing as
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;;; "Hello, world."
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;;;
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;;; These are useful for writing down long, constant strings -- such
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;;; as long, multi-line FORMAT strings, or arguments to Unix programs, e.g.
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;;; ;; Free up some disk space for my netnews files.
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;;; (run (csh -c #<EOF
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;;; cd /urops
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;;; rm -rf *
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;;; echo All done.
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;;;
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;;; EOF
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;;; ))
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;;;
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;;; The advantage they have over the double-quote syntax -- "Hello, world." --
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;;; is that there is no need to backslash-quote special characters internal
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;;; to the string, such as the double-quote or backslash characters.
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;;; Line-delimited here-string syntax:
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;;; The characters "#<<" introduce the here-string. The characters
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;;; between the "#<<" and the next newline are the *delimiter line*. *All* chars
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;;; between the "#<<" and the next newline comprise the delimiter line --
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;;; including any white space. The newline char separates the delimiter line
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;;; from the body of the string. The string body is terminated by a line of
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;;; text which exactly matches the delimiter line. This terminating line can
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;;; be ended by either a newline or end-of-file. Absolutely *no*
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;;; interpretation is done on the input string. Control chars, white space,
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;;; quotes, backslash chars -- everything is copied as-is. The newline
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;;; immediately preceding the terminating delimiter line is *not* included in
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;;; the result string (leave an extra blank line if you need to put a final
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;;; newline in the here string -- see the example above). If EOF is
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;;; encountered before reading the end of the here string, an error is
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;;; signalled.
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(define (read-here-string port)
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(make-immutable!
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(let ((delim-char (read-char port)))
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(cond ((eof-object? delim-char)
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(reading-error port "EOF while reading #< here-string delimiter."))
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((char=? delim-char #\<) ; It's a #<<EOF long here-string.
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(read-line-delimited-here-string port))
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;; It's short: #<|Here's the string.|
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(else (receive (str terminator)
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(read-delimited (char-set delim-char) port 'split)
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(if (eof-object? terminator)
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(reading-error port "EOF while reading #< here-string.")
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str)))))))
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(define (read-line-delimited-here-string port)
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;; First, read in the delimiter line.
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(let ((delim (read-line port)))
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(cond ((eof-object? delim)
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(reading-error port
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"EOF while reading #<< here-string delimiter line."))
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((= 1 (string-length delim))
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(reading-error port "#<< here-string empty delimiter line"))
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(else
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(let lp ((text '()))
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(receive (line terminator) (read-line port 'split)
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(cond ((equal? line delim)
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;; We're done. The last newline must be stripped
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;; off (with the CDR application).
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(if (pair? text)
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(apply string-append (reverse (cdr text)))
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""))
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((eof-object? terminator)
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(reading-error port "EOF while reading #<< here-string."))
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(else (lp `(,(string terminator) ,line . ,text))))))))))
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(define-sharp-macro #\<
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(lambda (c port)
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(read-char port) ; Snarf the first < char.
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(read-here-string port)))
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