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safe-simple-read.lisp
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safe-simple-read.lisp
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(in-package #:snooze-safe-simple-read)
(define-condition snooze-reader-error (simple-error reader-error) ())
(defmethod print-object ((c snooze-reader-error) s)
(print-unreadable-object (c s :type t)
(format s "~?"
(simple-condition-format-control c)
(simple-condition-format-arguments c))))
(defun parse-integer-then-float (string)
(let (retval nread)
(multiple-value-setq (retval nread)
(parse-integer string :junk-allowed t))
(cond ((/= nread (length string))
(multiple-value-setq (retval nread)
(ignore-errors
;; github#24: Sometimes SBCL will error here even with
;; :JUNK-ALLOWED. Swallow it.
(parse-float:parse-float string :junk-allowed t)))
(if (and retval
(/= nread (length string)))
(values nil nread)
(values retval nread)))
(t
(values retval nread)))))
(defun read-string (stream &optional (terminator #\") )
(unless (eql (read-char stream) terminator)
(error 'snooze-reader-error
:format-control "~a cannot read string that doesn't start with ~a"
:format-arguments (list 'parse-string terminator)))
(let ((nread 1))
(values
(handler-case
(with-output-to-string (*standard-output*)
(loop for c = (read-char stream) do
(incf nread)
(cond
((eql c terminator)
(return))
((eql c #\\)
(write-char (read-char stream)))
(t
(write-char c)))))
(end-of-file (e)
(error 'snooze-reader-error
:format-control "~a sees premature end reading string inside string (~a)"
:format-arguments (list 'parse-string e))))
nread)))
(defun read-name (stream)
(let* ((eof-sym (gensym))
(c (peek-char nil stream nil eof-sym)))
(cond ((eql c #\|)
(read-string stream #\|))
((eq c eof-sym)
(values nil 0))
(t
(let ((nread 0))
(values
(string-upcase
(with-output-to-string (*standard-output*)
(loop
with eof-sym = (gensym)
for c = (read-char stream nil eof-sym) do
(incf nread)
(cond ((eql c #\:)
(decf nread)
(unread-char c stream)
(return))
((eq c eof-sym) (decf nread) (return))
(t (write-char c))))))
nread))))))
(defun parse-symbol (string)
(let (symbol-name
(package *package*)
ncolons)
(with-input-from-string (stream string)
(multiple-value-bind (name nread)
(read-name stream)
(cond ((/= nread (length string))
(setq ncolons
(handler-case
(loop for c = (read-char stream)
while (eql c #\:)
count 1
finally (unread-char c stream))
(end-of-file (e)
(error 'snooze-reader-error
:format-control "~a sees a colon ending reading symbol from string ~a (~a)"
:format-arguments (list 'parse-symbol string e)))))
(cond ((= ncolons 0)
(error 'snooze-reader-error
:format-control "~a expecting colons reading symbol from string ~a"
:format-arguments (list 'parse-symbol string)))
((> ncolons 2)
(error 'snooze-reader-error
:format-control "~a sees too many colons reading symbol from string ~a"
:format-arguments (list 'parse-symbol string))))
(setq package (or (and (zerop (length name))
#.(find-package :keyword))
(find-package name)
(error 'snooze-reader-error
:format-control "~a does not recognize package ~a"
:format-arguments (list 'parse-symbol name))))
(multiple-value-bind (name more-nread)
(read-name stream)
(setq symbol-name name
nread (+ ncolons nread more-nread))
(when (/= nread (length string))
(error 'snooze-reader-error
:format-control "~a sees garbage reading symbol from string ~a"
:format-arguments (list 'parse-symbol string)))))
(t
(setq symbol-name name)))))
(multiple-value-bind (symbol status)
(find-symbol symbol-name package)
(when (and (eq status :internal)
ncolons
(/= ncolons 2))
(error 'snooze-reader-error
:format-control "~a sees a symbol ~a not external in the ~a package"
:format-arguments (list 'parse-symbol symbol-name package)))
(values symbol status symbol-name package))))
(defun safe-simple-read-from-string (string &optional make-symbol-p)
"Reads some objects represented by STRING.
Can only read in numbers, strings or existing symbols. Symbols may be
package-designated according to how they are written by of
WRITE-TO-STRING.
No new symbols are ever interned. A STRING value that would generate
interning of a symbol generates an error, but, if MAKE-SYMBOL-P is
non-NIL, a new uninterned symbol is returned with the name of the
would-be-interned symbol.
No macro-characters exist, not even #\(. So, where STRING would
normally represent a list to READ-FROM-STRING, it is taken as a
peculiar symbol name, that, at any rate, either exists in *PACKAGE* or
is never interned anywhere"
(cond
((zerop (length string))
(error 'snooze-reader-error
:format-control "Can't read from an empty string"))
((eql (aref string 0) #\")
(with-input-from-string (stream string)
(multiple-value-bind (obj nread)
(read-string stream #\")
(unless (= nread (length string))
(error 'snooze-reader-error
:format-control "~a sees junk reading string inside string ~s"
:format-arguments (list 'safe-read-simple-token-from-string string)))
(values obj nread))))
(t
(multiple-value-bind (number nread)
(parse-integer-then-float string)
(cond (number
(values number nread))
(t
(multiple-value-bind (symbol status symbol-name package)
(parse-symbol string)
(if status
(values symbol (length string))
(if make-symbol-p
(values (make-symbol symbol-name)
(length string))
(error 'snooze-reader-error
:format-control "~a refusing to intern a new symbol ~s in ~a"
:format-arguments `(safe-simple-read-from-string
,string
,package)))))))))))