A JSON grammar for nearley

json.ne

@{%
    const merge = d => d.join('');
    const nth = n => d => d[n];
%}

@builtin "whitespace.ne"

json -> _ object _                     {% nth(1) %}
      | _ array _                      {% nth(1) %}

object -> "{" _ "}"                    {% () => { return {}; } %}
        | "{" _ members _ "}"          {% nth(2) %}

members -> pair                        {% id %}
         | pair _ "," _ members        {% d => {
                                         for (var key in d[0]) {
                                            if (d[0].hasOwnProperty(key)) {
                                              d[4][key] = d[0][key];
                                            }
                                         }
                                         return d[4];
                                       } %}

pair -> string _ ":" _ value           {% d => { var x = {}; x[d[0]] = d[4]; return x; } %}

array -> "[" _ "]"                     {% () => [] %}
       | "[" _ elements _ "]"          {% nth(2) %}

elements -> value                      {% d => [d[0]] %}
          | value _ "," _ elements     {% d => [].concat(d[0], d[4]) %}

value -> string                        {% id %}
       | number                        {% d => parseFloat(d[0]) %}
       | object                        {% id %}
       | array                         {% id %}
       | "true"                        {% () => true %}
       | "false"                       {% () => false %}
       | "null"                        {% () => null %}

string -> "\"\""                       {% () => "" %}
        | "\"" chars "\""              {% nth(1) %}

chars -> char                          {% id %}
       | char chars                    {% merge %}

char -> [^"\\\x00-\x1F\x7F]            {% id %} # any Unicode character except " or \ or control character
      | "\\\""                         {% () => "\"" %}
      | "\\\\"                         {% () => "\\" %}
      | "\\/"                          {% () => "/" %}
      | "\\b"                          {% () => "\b" %}
      | "\\f"                          {% () => "\f" %}
      | "\\n"                          {% () => "\n" %}
      | "\\r"                          {% () => "\r" %}
      | "\\t"                          {% () => "\t" %}
      | "\\u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F]
                                       {% d => String.fromCharCode(d[1] + d[2] + d[3] + d[4]) %}

number -> int                          {% id %}
        | int frac                     {% merge %}
        | int exp                      {% merge %}
        | int frac exp                 {% merge %}

int -> digit                           {% id %}
     | digit19 digits                  {% merge %}
     | "-" digit                       {% merge %}
     | "-" digit19 digits              {% merge %}

frac -> "." digits                     {% merge %}

exp -> e digits                        {% merge %}

digits -> digit                        {% id %}
        | digit digits                 {% merge %}

digit -> [0-9]                         {% id %}

digit19 -> [1-9]                       {% id %}

e -> "e"                               {% id %}
   | "e+"                              {% id %}
   | "e-"                              {% id %}
   | "E"                               {% id %}
   | "E+"                              {% id %}
   | "E-"                              {% id %}

Usage:

npm install -g nearley
nearleyc -o json.js json.ne
nearley-test json.js < /your/nearest/package.json