Parser.scala

val space         = R( CharSets(" \n").rep1 )
val digits        = R( CharSets('0' to '9').rep1 )
val exponent      = R( CharSets("eE") ~ CharSets("+-").? ~ digits )
val fractional    = R( "." ~ digits )
val integral      = R( "0" | CharSets('1' to '9') ~ digits.rep )
val number        = R( "?".? ~ integral ~ fractional.? ~ exponent.? )
val `null`        = R( "null" )
val `false`       = R( "false" )
val `true`        = R( "true" )
val hexDigit      = R( CharSets('0'to'9', 'a'to'f', 'A'to'F') )
val unicodeEscape = R( "u" ~ hexDigit ~ hexDigit ~ hexDigit ~ hexDigit )
val escape        = R( "\\" ~ (CharSets("\"/\\bfnrt") | unicodeEscape) )
val string        = R( space.? ~ "\"" ~ (!"\"" ~ AnyChar | escape).rep ~ "\"")
val array         = R( ("[" ~! jsonExpr) ~ ("," ~! jsonExpr).rep ~ space.? ~ "]")
val pair          = R( string ~! ":" ~! jsonExpr )
val obj           = R( "{" ~! pair ~ ("," ~! pair).rep ~ space.? ~ "}" )
val jsonExpr: Parser[_] = R(space.? ~ (obj | array | string | `true` | `false` | `null` | number) ~ space.?)

Parsing:
{
    "firstName": John,
    "lastName": "Smith",
    "age": 25,
    "address": {
        "streetAddress": "21 2nd Street",
        "city": "New York",
        "state": "NY",
        "postalCode": 10021
    },
    "phoneNumbers": [
        {
            "type": "home",
            "number": "212 555-1234"
        },
        {
            "type": "fax",
            "number": "646 555-4567"
        }
    ]
}

Failure:
jsonExpr:0 / obj:1 / pair:2 / jsonExpr:19 / (obj | array | string | true | false | null | number):20 ..."John,\n    "

Parsing:
{
    "firstName": "John",
    "lastName": "Smith",
    "age": 25,
    "address": {
        "streetAddress": "21 2nd Street",
        "city": "New York",
        "state": "NY",
        "postalCode": 10021
    },
    "phoneNumbers": [
        {
            "type": "home",
            "number": "212 555-1234"
        },
        {
            "type": "fax",
            "number": "646 555-4567"
        }

}

Failure:
jsonExpr:0 / obj:1 / pair:212 / jsonExpr:232 / array:233 / "]":406 ..."} \n       "