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(in-package #:json)
(defparameter number-literal
(let ((signed-digits
(comp ((sign (optional (one-of (unit #\-)
(unit #\+))))
(natural (if sign
(crit (many (unit digit-char-p)))
(many (unit digit-char-p)))))
(cons sign natural))))
(comp ((base signed-digits)
(dot (optional (unit #\.)))
(fraction (if dot
(crit (many (unit digit-char-p)))
nothing))
(e (optional (one-of (unit #\e) (unit #\E))))
(exponent (if e
(crit signed-digits)
nothing)))
(read-from-string
(coerce
(remove nil (append base (cons dot fraction) (cons (when e #\d) exponent)))
'string)))))
(defparameter string-literal
(comp ((_ (unit #\"))
(chars (optional (many (one-of (comp ((slash (unit #\\))
(escaped (unit))
(codepoints (if (char= escaped #\u)
(repeat (unit digit-char-p) 4)
nothing)))
(case escaped
(#\n #\Newline)
(#\t #\Tab)
(#\u (read-from-string (coerce (append '(#\# #\\ #\u) codepoints) 'string)))
(t escaped)))
(unit (and (char/= it #\") (char/= it #\\)))))))
(_ (crit (unit #\"))))
(coerce chars 'string)))
(defparameter true-symbol
(comp ((_ (unit #\t))
(_ (crit (literal "rue"))))
'true))
(defparameter false-symbol
(comp ((_ (unit #\f))
(_ (crit (literal "alse"))))
'false))
(defparameter null-symbol
(comp ((_ (unit #\n))
(_ (crit (literal "ull"))))
'null))
(defvar json-value)
(defparameter json-array
(comp ((_ (unit #\[))
(vn (optional (separated-list json-value (unit #\,))))
(_ (unit #\])))
(apply #'vector vn)))
(defparameter json-object
(let ((json-pair
(comp ((_ whitespace)
(k string-literal)
(_ whitespace)
(_ (crit (unit #\:)))
(v (crit json-value)))
(cons k v))))
(comp ((_ (unit #\{))
(vn (optional (separated-list json-pair (unit #\,))))
(_ (unit #\})))
(let* ((obj (make-hash-table :test #'equal :size (length vn))))
(dolist (v vn)
(setf (gethash (car v) obj) (cdr v)))
obj))))
(defparameter json-value
(comp ((_ whitespace)
(v (one-of number-literal
string-literal
json-object
json-array
true-symbol
false-symbol
null-symbol))
(_ whitespace))
v))
(defun from-string (str)
(run json-value (input:from-string str)))
(defun from-file (file)
(run json-value (input:from-file file)))
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