[PATCH] ice-9: Add JSON module.

[David Thompson]

Hello Guilers,

JSON is an commonly encountered format when writing web applications,
much like XML, and I think it would be a good idea if the core Guile
distribution had an SXML equivalent for JSON.  This patch introduces
such an interface in the (ice-9 json) module.

With (ice-9 json), this expression:

    (@ (name . "Eva Luator")
       (age . 24)
       (schemer . #t)
       (hobbies "hacking" "cycling" "surfing"))

serializes to this JSON (except not pretty-printed):

    {
      "name": "Eva Luator",
      "age": 24,
      "schemer": true,
      "hobbies": [
        "hacking",
        "cycling",
        "surfing"
      ]
    }

Thanks to Mark Weaver and Chris Webber for helping come to a consensus
on a good syntax for JSON objects.

>From 2d4d8607aedaede98f413a84f135d8798d506233 Mon Sep 17 00:00:00 2001
From: David Thompson <address@hidden>
Date: Sat, 15 Aug 2015 14:09:23 -0400
Subject: [PATCH] ice-9: Add JSON module.

* module/ice-9/json.scm: New file.
* module/Makefile.am (ICE_9_SOURCES): Add it.
* test-suite/tests/json.test: New file.
* test-suite/Makefile.am (SCM_TESTS): Add it.
* doc/ref/guile.texi ("Guile Modules"): Add "JSON" section.
* doc/ref/json.texi: New file.
* doc/ref/Makefile.am (guile_TEXINFOS): Add it.
---
 doc/ref/Makefile.am        |   3 +-
 doc/ref/guile.texi         |   2 +
 doc/ref/json.texi          |  62 +++++++
 module/Makefile.am         |   3 +-
 module/ice-9/json.scm      | 395 +++++++++++++++++++++++++++++++++++++++++++++
 test-suite/Makefile.am     |   1 +
 test-suite/tests/json.test | 149 +++++++++++++++++
 7 files changed, 613 insertions(+), 2 deletions(-)
 create mode 100644 doc/ref/json.texi
 create mode 100644 module/ice-9/json.scm
 create mode 100644 test-suite/tests/json.test

diff --git a/doc/ref/Makefile.am b/doc/ref/Makefile.am
index 31c26a7..5dfc019 100644
--- a/doc/ref/Makefile.am
+++ b/doc/ref/Makefile.am
@@ -95,7 +95,8 @@ guile_TEXINFOS = preface.texi                 \
                 goops.texi                     \
                 goops-tutorial.texi            \
                 guile-invoke.texi              \
-                effective-version.texi
+                effective-version.texi         \
+                json.texi
 
 ETAGS_ARGS = $(info_TEXINFOS) $(guile_TEXINFOS)
 
diff --git a/doc/ref/guile.texi b/doc/ref/guile.texi
index db815eb..468d3a5 100644
--- a/doc/ref/guile.texi
+++ b/doc/ref/guile.texi
@@ -375,6 +375,7 @@ available through both Scheme and C interfaces.
 * Statprof::                    An easy-to-use statistical profiler.
 * SXML::                        Parsing, transforming, and serializing XML.
 * Texinfo Processing::          Munging documents written in Texinfo.
+* JSON::                        Parsing and serializing JSON.
 @end menu
 
 @include slib.texi
@@ -397,6 +398,7 @@ available through both Scheme and C interfaces.
 @include statprof.texi
 @include sxml.texi
 @include texinfo.texi
address@hidden json.texi
 
 @include goops.texi
 
diff --git a/doc/ref/json.texi b/doc/ref/json.texi
new file mode 100644
index 0000000..43dba4d
--- /dev/null
+++ b/doc/ref/json.texi
@@ -0,0 +1,62 @@
address@hidden -*-texinfo-*-
address@hidden This is part of the GNU Guile Reference Manual.
address@hidden Copyright (C) 2015  Free Software Foundation, Inc.
address@hidden See the file guile.texi for copying conditions.
address@hidden
+
address@hidden JSON
address@hidden JSON
+
address@hidden json
address@hidden (ice-9 json)
+
+The @code{(ice-9 json)} module provides procedures for parsing and
+serializing JSON, the JavaScript Object Notation data interchange
+format.  For example, the JSON document:
+
address@hidden
address@hidden
+{
+  "name": "Eva Luator",
+  "age": 24,
+  "schemer": true,
+  "hobbies": [
+    "hacking",
+    "cycling",
+    "surfing"
+  ]
+}
address@hidden verbatim
address@hidden example
+
+may be represented with the following s-expression:
+
address@hidden
address@hidden
+(@ (name . "Eva Luator")
+   (age . 24)
+   (schemer . #t)
+   (hobbies "hacking" "cycling" "surfing"))
address@hidden verbatim
address@hidden example
+
+Strings, real numbers, @code{#t}, @code{#f}, @code{#nil}, lists, and
+association lists may be serialized as JSON.  Association lists
+serialize to objects, and regular lists serialize to arrays.  To
+distinguish regular lists from association lists, the @code{@@} symbol
+is used to ``tag'' the association list as a JSON object, as in the
+above example.  The keys of association lists may be either strings or
+symbols.
+
address@hidden {Scheme Procedure} read-json port
+
+Parse JSON-encoded text from @var{port} and return its s-expression
+representation.
+
address@hidden deffn
+
address@hidden {Scheme Procedure} write-json exp port
+
+Write the expression @var{exp} as JSON-encoded text to @var{port}.
+
address@hidden deffn
diff --git a/module/Makefile.am b/module/Makefile.am
index 7e96de7..6380953 100644
--- a/module/Makefile.am
+++ b/module/Makefile.am
@@ -256,7 +256,8 @@ ICE_9_SOURCES = \
   ice-9/list.scm \
   ice-9/serialize.scm \
   ice-9/local-eval.scm \
-  ice-9/unicode.scm
+  ice-9/unicode.scm \
+  ice-9/json.scm
 
 srfi/srfi-64.go: srfi/srfi-64.scm srfi/srfi-64/testing.scm
 
diff --git a/module/ice-9/json.scm b/module/ice-9/json.scm
new file mode 100644
index 0000000..3850ee4
--- /dev/null
+++ b/module/ice-9/json.scm
@@ -0,0 +1,395 @@
+;;;; json.scm --- JSON reader/writer
+;;;; Copyright (C) 2015 Free Software Foundation, Inc.
+;;;;
+;;;; This library is free software; you can redistribute it and/or
+;;;; modify it under the terms of the GNU Lesser General Public
+;;;; License as published by the Free Software Foundation; either
+;;;; version 3 of the License, or (at your option) any later version.
+;;;;
+;;;; This library is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;;; Lesser General Public License for more details.
+;;;;
+;;;; You should have received a copy of the GNU Lesser General Public
+;;;; License along with this library; if not, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 
USA
+;;;;
+
+(define-module (ice-9 json)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:export (read-json write-json))
+
+;;;
+;;; Reader
+;;;
+
+(define (json-error port)
+  (throw 'json-error port))
+
+(define (assert-char port char)
+  "Read a character from PORT and throw an invalid JSON error if the
+character is not CHAR."
+  (unless (eqv? (read-char port) char)
+    (json-error port)))
+
+(define (whitespace? char)
+  "Return #t if CHAR is a whitespace character."
+  (char-set-contains? char-set:whitespace char))
+
+(define (consume-whitespace port)
+  "Discard characters from PORT until a non-whitespace character is
+encountered.."
+  (match (peek-char port)
+    ((? eof-object?) *unspecified*)
+    ((? whitespace?)
+     (read-char port)
+     (consume-whitespace port))
+    (_ *unspecified*)))
+
+(define (make-keyword-reader keyword value)
+  "Parse the keyword symbol KEYWORD as VALUE."
+  (let ((str (symbol->string keyword)))
+    (lambda (port)
+      (let loop ((i 0))
+        (cond
+         ((= i (string-length str)) value)
+         ((eqv? (string-ref str i) (read-char port))
+          (loop (1+ i)))
+         (else (json-error port)))))))
+
+(define read-true (make-keyword-reader 'true #t))
+(define read-false (make-keyword-reader 'false #f))
+(define read-null (make-keyword-reader 'null #nil))
+
+(define (read-hex-digit port)
+  "Read a hexadecimal digit from PORT."
+  (match (read-char port)
+    (#\0 0)
+    (#\1 1)
+    (#\2 2)
+    (#\3 3)
+    (#\4 4)
+    (#\5 5)
+    (#\6 6)
+    (#\7 7)
+    (#\8 8)
+    (#\9 9)
+    ((or #\A #\a) 10)
+    ((or #\B #\b) 11)
+    ((or #\C #\c) 12)
+    ((or #\D #\d) 13)
+    ((or #\E #\e) 14)
+    ((or #\F #\f) 15)
+    (_ (json-error port))))
+
+(define (read-utf16-character port)
+  "Read a hexadecimal encoded UTF-16 character from PORT."
+  (integer->char
+   (+ (* (read-hex-digit port) (expt 16 3))
+      (* (read-hex-digit port) (expt 16 2))
+      (* (read-hex-digit port) 16)
+      (read-hex-digit port))))
+
+(define (read-escape-character port)
+  "Read escape character from PORT."
+  (match (read-char port)
+    (#\" #\")
+    (#\\ #\\)
+    (#\/ #\/)
+    (#\b #\backspace)
+    (#\f #\page)
+    (#\n #\newline)
+    (#\r #\return)
+    (#\t #\tab)
+    (#\u (read-utf16-character port))
+    (_ (json-error port))))
+
+(define (read-string port)
+  "Read a JSON encoded string from PORT."
+  (assert-char port #\")
+  (let loop ((result '()))
+    (match (read-char port)
+      ((? eof-object?) (json-error port))
+      (#\" (list->string (reverse result)))
+      (#\\ (loop (cons (read-escape-character port) result)))
+      (char (loop (cons char result))))))
+
+(define char-set:json-digit
+  (char-set #\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9))
+
+(define (digit? char)
+  (char-set-contains? char-set:json-digit char))
+
+(define (read-digit port)
+  "Read a digit 0-9 from PORT."
+  (match (read-char port)
+    (#\0 0)
+    (#\1 1)
+    (#\2 2)
+    (#\3 3)
+    (#\4 4)
+    (#\5 5)
+    (#\6 6)
+    (#\7 7)
+    (#\8 8)
+    (#\9 9)
+    (else (json-error port))))
+
+(define (read-digits port)
+  "Read a sequence of digits from PORT."
+  (let loop ((result '()))
+    (match (peek-char port)
+      ((? eof-object?)
+       (reverse result))
+      ((? digit?)
+       (loop (cons (read-digit port) result)))
+      (else (reverse result)))))
+
+(define (read-zeroes port)
+  "Read a sequence of zeroes from PORT."
+  (let loop ((result '()))
+    (match (peek-char port)
+      ((? eof-object?)
+       result)
+      (#\0
+       (read-char port)
+       (loop (cons 0 result)))
+      (else result))))
+
+(define (list->integer digits)
+  "Convert the list DIGITS to an integer."
+  (let loop ((i (1- (length digits)))
+             (result 0)
+             (digits digits))
+    (match digits
+      (() result)
+      ((n . tail)
+       (loop (1- i)
+             (+ result (* n (expt 10 i)))
+             tail)))))
+
+(define (read-positive-integer port)
+  "Read a positive integer with no leading zeroes from PORT."
+  (match (read-digits port)
+    ((0 . _)
+     (json-error port)) ; no leading zeroes allowed
+    ((digits ...)
+     (list->integer digits))))
+
+(define (read-exponent port)
+  "Read exponent from PORT."
+  (define (read-expt)
+    (list->integer (read-digits port)))
+
+  (unless (memv (read-char port) '(#\e #\E))
+    (json-error port))
+
+  (match (peek-char port)
+    ((? eof-object?)
+     (json-error port))
+    (#\-
+     (read-char port)
+     (- (read-expt)))
+    (#\+
+     (read-char port)
+     (read-expt))
+    ((? digit?)
+     (read-expt))
+    (_ (json-error port))))
+
+(define (read-fraction port)
+  "Read fractional number part from PORT as an inexact number."
+  (let* ((digits      (read-digits port))
+         (numerator   (list->integer digits))
+         (denomenator (expt 10 (length digits))))
+    (/ numerator denomenator)))
+
+(define (read-positive-number port)
+  "Read a positive number from PORT."
+  (let* ((integer (match (peek-char port)
+                    ((? eof-object?)
+                     (json-error port))
+                    (#\0
+                     (read-char port)
+                     0)
+                    ((? digit?)
+                     (read-positive-integer port))
+                    (_ (json-error port))))
+         (fraction (match (peek-char port)
+                     (#\.
+                      (read-char port)
+                      (read-fraction port))
+                     (_ 0)))
+         (exponent (match (peek-char port)
+                     ((or #\e #\E)
+                      (read-exponent port))
+                     (_ 0)))
+         (n (* (+ integer fraction) (expt 10 exponent))))
+
+    ;; Keep integers as exact numbers, but convert numbers encoded as
+    ;; floating point numbers to an inexact representation.
+    (if (zero? fraction)
+        n
+        (exact->inexact n))))
+
+(define (read-number port)
+  "Read a number from PORT"
+  (match (peek-char port)
+    ((? eof-object?)
+     (json-error port))
+    (#\-
+     (read-char port)
+     (- (read-positive-number port)))
+    ((? digit?)
+     (read-positive-number port))
+    (_ (json-error port))))
+
+(define (read-object port)
+  "Read key/value map from PORT."
+  (define (read-key+value-pair)
+    (let ((key (read-string port)))
+      (consume-whitespace port)
+      (assert-char port #\:)
+      (consume-whitespace port)
+      (let ((value (read-value port)))
+        (cons key value))))
+
+  (assert-char port #\{)
+  (consume-whitespace port)
+
+  (if (eqv? #\} (peek-char port))
+      (begin
+        (read-char port)
+        '(@)) ; empty object
+      (let loop ((result (list (read-key+value-pair))))
+        (consume-whitespace port)
+        (match (peek-char port)
+          (#\, ; read another value
+           (read-char port)
+           (consume-whitespace port)
+           (loop (cons (read-key+value-pair) result)))
+          (#\} ; end of object
+           (read-char port)
+           (cons '@ (reverse result)))
+          (_ (json-error port))))))
+
+(define (read-array port)
+  "Read array from PORT."
+  (assert-char port #\[)
+  (consume-whitespace port)
+
+  (if (eqv? #\] (peek-char port))
+      (begin
+        (read-char port)
+        '()) ; empty array
+      (let loop ((result (list (read-value port))))
+        (consume-whitespace port)
+        (match (peek-char port)
+          (#\, ; read another value
+           (read-char port)
+           (consume-whitespace port)
+           (loop (cons (read-value port) result)))
+          (#\] ; end of array
+           (read-char port)
+           (reverse result))
+          (_ (json-error port))))))
+
+(define (read-value port)
+  "Read a JSON value from PORT."
+  (consume-whitespace port)
+  (match (peek-char port)
+    ((? eof-object?) (json-error port))
+    (#\" (read-string port))
+    (#\{ (read-object port))
+    (#\[ (read-array port))
+    (#\t (read-true port))
+    (#\f (read-false port))
+    (#\n (read-null port))
+    ((or #\- (? digit?))
+     (read-number port))
+    (_ (json-error port))))
+
+(define (read-json port)
+  "Read JSON text from port and return an s-expression representation."
+  (let ((result (read-value port)))
+    (consume-whitespace port)
+    (unless (eof-object? (peek-char port))
+      (json-error port))
+    result))
+
+
+;;;
+;;; Writer
+;;;
+
+(define (write-string str port)
+  "Write STR to PORT in JSON string format."
+  (define (escape-char char)
+    (display (match char
+               (#\" "\\\"")
+               (#\\ "\\\\")
+               (#\/ "\\/")
+               (#\backspace "\\b")
+               (#\page "\\f")
+               (#\newline "\\n")
+               (#\return "\\r")
+               (#\tab "\\t")
+               (_ char))
+             port))
+
+  (display "\"" port)
+  (string-for-each escape-char str)
+  (display "\"" port))
+
+(define (write-object alist port)
+  "Write ALIST to PORT in JSON object format."
+  ;; Keys may be strings or symbols.
+  (define key->string
+    (match-lambda
+     ((? string? key) key)
+     ((? symbol? key) (symbol->string key))))
+
+  (define (write-pair pair)
+    (match pair
+      ((key . value)
+       (write-string (key->string key) port)
+       (display ":" port)
+       (write-json value port))))
+
+  (display "{" port)
+  (match alist
+    (() #f)
+    ((front ... end)
+     (for-each (lambda (pair)
+                 (write-pair pair)
+                 (display "," port))
+          front)
+     (write-pair end)))
+  (display "}" port))
+
+(define (write-array lst port)
+  "Write LST to PORT in JSON array format."
+  (display "[" port)
+  (match lst
+    (() #f)
+    ((front ... end)
+     (for-each (lambda (val)
+                 (write-json val port)
+                 (display "," port))
+               front)
+     (write-json end port)))
+  (display "]" port))
+
+(define (write-json exp port)
+  "Write EXP to PORT in JSON format."
+  (match exp
+    (#t (display "true" port))
+    (#f (display "false" port))
+    ;; Differentiate #nil from '().
+    ((and (? boolean? ) #nil) (display "null" port))
+    ((? string? s) (write-string s port))
+    ((? real? n) (display n port))
+    (('@ . alist) (write-object alist port))
+    ((vals ...) (write-array vals port))))
diff --git a/test-suite/Makefile.am b/test-suite/Makefile.am
index 3b10353..cbdfa7d 100644
--- a/test-suite/Makefile.am
+++ b/test-suite/Makefile.am
@@ -71,6 +71,7 @@ SCM_TESTS = tests/00-initial-env.test         \
            tests/iconv.test                    \
            tests/import.test                   \
            tests/interp.test                   \
+           tests/json.test                     \
            tests/keywords.test                 \
            tests/list.test                     \
            tests/load.test                     \
diff --git a/test-suite/tests/json.test b/test-suite/tests/json.test
new file mode 100644
index 0000000..c94a1c7
--- /dev/null
+++ b/test-suite/tests/json.test
@@ -0,0 +1,149 @@
+;;;; json.test --- test JSON reader/writer     -*- scheme -*-
+;;;;
+;;;; Copyright (C) 2015 Free Software Foundation, Inc.
+;;;;
+;;;; This library is free software; you can redistribute it and/or
+;;;; modify it under the terms of the GNU Lesser General Public
+;;;; License as published by the Free Software Foundation; either
+;;;; version 3 of the License, or (at your option) any later version.
+;;;;
+;;;; This library is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;;; Lesser General Public License for more details.
+;;;;
+;;;; You should have received a copy of the GNU Lesser General Public
+;;;; License along with this library; if not, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 
USA
+
+(define-module (test-suite test-json)
+  #:use-module (test-suite lib)
+  #:use-module (ice-9 json))
+
+;;;
+;;; Reader
+;;;
+
+(define (read-json-string str)
+  (call-with-input-string str read-json))
+
+(define (json-read=? str x)
+  (= x (read-json-string str)))
+
+(define (json-read-eq? str x)
+  (eq? x (read-json-string str)))
+
+(define (json-read-equal? str x)
+  (equal? x (read-json-string str)))
+
+(define (json-read-string=? str x)
+  (string=? x (read-json-string str)))
+
+(with-test-prefix "read-json"
+  (pass-if (json-read-eq? "true" #t))
+  (pass-if (json-read-eq? "false" #f))
+  (pass-if (json-read-eq? "null" #nil))
+  (pass-if (json-read=? "0" 0))
+  (pass-if (json-read=? "0.1" 0.1))
+  (pass-if (json-read=? "1" 1))
+  (pass-if (json-read=? "-1" -1))
+  (pass-if (json-read=? "1.1" 1.1))
+  (pass-if (json-read=? "1e2" 1e2))
+  (pass-if (json-read=? "1.1e2" 1.1e2))
+  (pass-if (json-read=? "1.1e-2" 1.1e-2))
+  (pass-if (json-read=? "1.1e+2" 1.1e2))
+  (pass-if (json-read=? "1.1e+02" 1.1e2))
+  (pass-if (json-read-string=? "\"foo\"" "foo"))
+  ;; \" escape code.
+  (pass-if (json-read-string=? "\"\\\"\"" "\""))
+  ;; \\ escape code.
+  (pass-if (json-read-string=? "\"\\\\\"" "\\"))
+  ;; \/ escape code.
+  (pass-if (json-read-string=? "\"\\/\"" "/"))
+  ;; \b escape code.
+  (pass-if (json-read-string=? "\"\\b\"" "\b"))
+  ;; \f escape code.
+  (pass-if (json-read-string=? "\"\\f\"" "\f"))
+  ;; \n escape code.
+  (pass-if (json-read-string=? "\"\\n\"" "\n"))
+  ;; \r escape code.
+  (pass-if (json-read-string=? "\"\\r\"" "\r"))
+  ;; \t escape code.
+  (pass-if (json-read-string=? "\"\\t\"" "\t"))
+  ;; Unicode in hexadecimal format.
+  (pass-if (json-read-string=? "\"\\u12ab\"" "\u12ab"))
+  (pass-if (json-read-equal? "{}" '(@)))
+  (pass-if (json-read-equal? "{ \"foo\": \"bar\", \"baz\": \"frob\"}"
+                             '(@ ("foo" . "bar") ("baz" . "frob"))))
+  ;; Nested objects.
+  (pass-if (json-read-equal? "{\"foo\":{\"bar\":\"baz\"}}"
+                             '(@ ("foo" . (@ ("bar" . "baz"))))))
+  (pass-if (json-read-eq? "[]" '()))
+  (pass-if (json-read-equal? "[1, 2, \"foo\"]"
+                             '(1 2 "foo")))
+  ;; Nested arrays.
+  (pass-if (json-read-equal? "[1, 2, [\"foo\", \"bar\"]]"
+                             '(1 2 ("foo" "bar"))))
+  ;; Arrays and objects nested in each other.
+  (pass-if (json-read-equal? "{\"foo\":[{\"bar\":true},{\"baz\":[1,2,3]}]}"
+                             '(@ ("foo" . ((@ ("bar" . #t))
+                                           (@ ("baz" . (1 2 3))))))))
+  ;; Leading/trailing whitespace.
+  (pass-if (json-read-eq? "  true  " #t)))
+
+;;;
+;;; Writer
+;;;
+
+(define (write-json-string exp)
+  (call-with-output-string
+   (lambda (port)
+     (write-json exp port))))
+
+(define (json-write-string=? exp str)
+  (string=? str (write-json-string exp)))
+
+(with-test-prefix "write-json"
+  (pass-if (json-write-string=? #t "true"))
+  (pass-if (json-write-string=? #f "false"))
+  (pass-if (json-write-string=? #nil "null"))
+  (pass-if (json-write-string=? 0 "0"))
+  (pass-if (json-write-string=? 0.1 "0.1"))
+  (pass-if (json-write-string=? 1 "1"))
+  (pass-if (json-write-string=? -1 "-1"))
+  (pass-if (json-write-string=? 1.1 "1.1"))
+  (pass-if (json-write-string=? "foo" "\"foo\""))
+  ;; \" escape code.
+  (pass-if (json-write-string=? "\"" "\"\\\"\""))
+  ;; \\ escape code.
+  (pass-if (json-write-string=? "\\" "\"\\\\\""))
+  ;; \/ escape code.
+  (pass-if (json-write-string=? "/" "\"\\/\""))
+  ;; \b escape code.
+  (pass-if (json-write-string=? "\b" "\"\\b\""))
+  ;; \f escape code.
+  (pass-if (json-write-string=? "\f" "\"\\f\""))
+  ;; \n escape code.
+  (pass-if (json-write-string=? "\n" "\"\\n\""))
+  ;; \r escape code.
+  (pass-if (json-write-string=? "\r" "\"\\r\""))
+  ;; \t escape code.
+  (pass-if (json-write-string=? "\t" "\"\\t\""))
+  (pass-if (json-write-string=? '(@) "{}"))
+  (pass-if (json-write-string=? '(@ ("foo" . "bar") ("baz" . "frob"))
+                                "{\"foo\":\"bar\",\"baz\":\"frob\"}"))
+  ;; Nested objects.
+  (pass-if (json-write-string=? '(@ ("foo" . (@ ("bar" . "baz"))))
+                                "{\"foo\":{\"bar\":\"baz\"}}"))
+  (pass-if (json-write-string=? '() "[]"))
+  (pass-if (json-write-string=? '(1 2 "foo")
+                                "[1,2,\"foo\"]"))
+  ;; Nested arrays.
+  (pass-if (json-write-string=? '(1 2 ("foo" "bar"))
+                                "[1,2,[\"foo\",\"bar\"]]"))
+  ;; Arrays and objects nested in each other.
+  (pass-if (json-write-string=? '(@ ("foo" . ((@ ("bar" . #t))
+                                              (@ ("baz" . (1 2))))))
+                                "{\"foo\":[{\"bar\":true},{\"baz\":[1,2]}]}"))
+  ;; Symbol keys in alists
+  (pass-if (json-write-string=? '(@ (foo . 1)) "{\"foo\":1}")))
-- 
2.4.3

-- 
David Thompson
GPG Key: 0FF1D807