Here is the grammar:

<json> ::=              <value> | <fn-def> <json>
<value> ::=             <object> | <array> | <string> | <number> | <bool>
                        | <fn-def> | <fn-app>
                        | "null"
<object> ::=            "{" [ <member> { "," <member> } ] "}"
<member> ::=            <string> ":" <value>
<string> ::=            "\"" { <char> } "\""
<char> ::=              (ASCII other than "\"", "\\", 0-31, 127-159)
                        | (Unicode other than ASCII)
                        | ( "\\" (
                            "\"" | "\\" | "/" | "b" | "f" | "n" | "r" | "t"
                            | "u" <hex> <hex> <hex> <hex>
                        )
<hex> ::=               /A-Fa-f0-9/
<array> ::=             "[" [ <value> { "," <value> } ] "]"
<number> ::=            <integer> [ <fraction> ] [ <exponent> ]
<integer> ::=           "0" | /[1-9]+/ | "-" <integer>
<fractional> ::=        "." /[0-9]+/
<exponent> ::=          ("E" | "e") [ "-" | "+" ] /[0-9]+/
<bool> ::=              "true" | "false"
<fn-def> ::=            "(" <ident> { <ident> }
                            ("->" <value> | ":" <string> <string>) ")"
<ident> ::=             <startc> { <identc> }
<startc> ::=            /A-Za-z_/ or non-ASCII Unicode
<identc> ::=            <startc> | /[0-9-]/
<fn-app> ::=            "(" <ident> { <value> } ")"
<var> ::=               "$" <ident>