I post a partial solution to the off-side-reader quiz. I say "partial" because, even though it reads in off-side mode, I'm not sure if it works as it is supposed in every case, i.e.: - what about blank lines? - what about comments? - the !# is supposed to be alone in a single line? - ...

I'm afraid I tend overuse format and loop.

It is also possibly very inefficient: it generates a new string with the "correct", inherent, parens made explicit, then reads it.

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(defpackage :quiz2) (in-package :quiz2)

(defvar *blanks* '(#\Space #\Tab #\Newline #\Return))

(defun distance (str prev-dist) (if (zerop (length (string-left-trim *blanks* str))) prev-dist (do ((col 0 (1+ col))) ((not (member (aref str col) *blanks* :test #'char=)) col))))

(defun read-off-side-to-string (stream) (let ((prev-line "") (prev-dists '()) (prev-dist 0)) (with-output-to-string (s) (format s "(progn ") (loop for line = (read-line stream nil 'eof) while (not (or (eq line 'eof) (string= line "!#"))) do (let ((dist (distance line prev-dist))) (when (> dist prev-dist) (push dist prev-dists) (format s "(")) (format s "~A~%" prev-line) (loop while (and (not (null prev-dists)) (< dist (car prev-dists))) do (pop prev-dists) do (format s ")")) (setf prev-line line) (setf prev-dist dist))) (format s "~A~%" prev-line) (loop while (not (null prev-dists)) do (pop prev-dists) do (format s ")")) (format s ")~%"))))

(defun read-off-side (stream c n) (nth-value 0 (read-from-string (read-off-side-to-string stream))))

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