I am trying to make a reader macro that would convert @this into "this". This is what I currently have:
(defun string-reader (stream char)
(declare (ignore char))
(format nil "\"~a\"" (read-line stream t nil t))
)
(set-macro-character #\@ #'string-reader )
The problem is that this requires that I put a newline after ever @this. I've also tried it with (read), but that just returns the variable test, which has not been set. I can't just hard-code the number of characters after the @ symbol, because I don't know how many there would be. Is there any way to fix this?
Edit: is the only way to do this to loop over read-char and peek-char, reading until I get to #),#\space, or #\Newline?
You can try to use read and then look at what it returns:
(defun string-reader (stream char)
(declare (ignore char))
(let ((this (let ((*readtable* (copy-readtable)))
(setf (readtable-case *readtable*) :preserve)
(read stream t nil t))))
(etypecase this
(string this)
(symbol (symbol-name this)))))
(set-macro-character #\@ #'string-reader)
Above would allow @This and @"This", but not @333.
This version just reads a string until whitespace:
(defun read-as-string-until-whitespace (stream)
(with-output-to-string (out-stream)
(loop for next = (peek-char nil stream t nil t)
until (member next '(#\space #\newline #\tab))
do (write-char (read-char stream t nil t) out-stream))))
(defun string-reader (stream char)
(declare (ignore char))
(read-as-string-until-whitespace stream))
(set-macro-character #\@ #'string-reader)
Example:
CL-USER 21 > @this
"this"
CL-USER 22 > @42
"42"
CL-USER 23 > @FooBar
"FooBar"