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(in-package #:json)
(defun the-char (c)
(unit (lambda (x) (char= c x))))
(defun some-char (&rest char-list)
(unit (lambda (x) (find x char-list))))
(defun not-these-chars (&rest char-list)
(unit (lambda (x) (not (find x char-list)))))
(defparameter number-literal
(let ((signed-digits
(comp ((sign (zero-or-one (some-char #\- #\+)))
(natural (if sign
(either (one-or-more (unit #'digit-char-p))
(fail "Malformed number."))
(one-or-more (unit #'digit-char-p)))))
(cons sign natural))))
(comp ((base signed-digits)
(dot (zero-or-one (the-char #\.)))
(fraction (if dot
(either (one-or-more (unit #'digit-char-p))
(fail "Malformed fractional part."))
nothing))
(e (zero-or-one (some-char #\e #\E)))
(exponent (if e
(either signed-digits
(fail "Malformed exponent part."))
nothing)))
(read-from-string
(str:from-list
(remove nil (append base (cons dot fraction) (cons e exponent))))))))
(defparameter string-literal
(comp ((_ (the-char #\"))
(chars (zero-or-more (either (comp ((slash (the-char #\\))
(escaped (unit))
(codepoints (if (char= escaped #\u)
(comp ((cp0 (unit #'digit-char-p))
(cp1 (unit #'digit-char-p))
(cp2 (unit #'digit-char-p))
(cp3 (unit #'digit-char-p)))
(let ((str (make-string 7)))
(setf (char str 0) #\#)
(setf (char str 1) #\\)
(setf (char str 2) #\u)
(setf (char str 3) cp0)
(setf (char str 4) cp1)
(setf (char str 5) cp2)
(setf (char str 6) cp3)
str))
nothing)))
(case escaped
(#\n
#\Newline)
(#\t
#\Tab)
(#\u
(read-from-string codepoints))
(t escaped)))
(not-these-chars #\" #\\))))
(_ (either (the-char #\")
(fail "String is not properly closed."))))
(str:from-list chars)))
(defparameter whitespace
(comp ((_ (zero-or-more (some-char #\Space #\Newline #\Tab))))
nil))
(defparameter true-symbol
(comp ((_ (the-char #\t))
(_ (either (comp ((_ (the-char #\r))
(_ (the-char #\u))
(_ (the-char #\e)))
nil)
(fail "Expected 'true'."))))
'true))
(defparameter false-symbol
(comp ((_ (the-char #\f))
(_ (either (comp ((_ (the-char #\a))
(_ (the-char #\l))
(_ (the-char #\s))
(_ (the-char #\e)))
nil)
(fail "Expected 'false'."))))
'false))
(defparameter null-symbol
(comp ((_ (the-char #\n))
(_ (either (comp ((_ (the-char #\u))
(_ (the-char #\l))
(_ (the-char #\l)))
nil)
(fail "Expected 'null'."))))
'null))
(defvar json-value)
(defun separated-list (value-type separator)
(comp ((v value-type)
(sep (zero-or-one (the-char separator)))
(vn (if sep
(either (separated-list value-type separator)
(fail "Expected another value."))
nothing)))
(cons v vn)))
(defparameter json-array
(comp ((_ (the-char #\[))
(vn (zero-or-one (separated-list json-value #\,)))
(_ (the-char #\])))
(apply #'vector vn)))
(defparameter json-object
(let ((json-pair
(comp ((_ whitespace)
(k (either string-literal
(fail "Expected a string.")))
(_ whitespace)
(_ (either (the-char #\:)
(fail "Expected a \":\"")))
(v json-value))
(cons k v))))
(comp ((_ (the-char #\{))
(vn (zero-or-one (separated-list json-pair #\,)))
(_ (the-char #\})))
(let* ((obj (make-hash-table :test #'equal :size (length vn))))
(dolist (v vn)
(setf (gethash (car v) obj) (cdr v)))
obj))))
(setf json-value
(comp ((_ whitespace)
(v (either number-literal
string-literal
json-object
json-array
true-symbol
false-symbol
null-symbol))
(_ whitespace))
v))
(defun parse-string (str)
(run json-value (input:from-string str)))
(defun parse-file (file)
(run json-value (input:from-file file)))
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