После 6.5 лет забвения автор выпустил версию 0.2.0 header-only библиотеки lug.
using namespace lug::language;
rule JSON;
rule ExponentPart = lexeme[ "[Ee]"_rx > ~"[+-]"_rx > +"[0-9]"_rx ];
rule FractionalPart = lexeme[ "."_sx > +"[0-9]"_rx ];
rule IntegralPart = lexeme[ "0"_sx | "[1-9]"_rx > *"[0-9]"_rx ];
rule Number = lexeme[ ~"-"_sx > IntegralPart > ~FractionalPart > ~ExponentPart ];
rule Boolean = lexeme[ "true"_sx | "false" ];
rule Null = lexeme[ "null" ];
rule UnicodeEscape = lexeme[ 'u' > "[0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f]"_rx ];
rule Escape = lexeme[ "\\" > ("[/\\bfnrt]"_rx | UnicodeEscape) ];
rule String = lexeme[ "\"" > *("[^\"\\\u0000-\u001F]"_rx | Escape) > "\"" ];
rule Array = "[" > JSON > *("," > JSON) > "]";
rule Object = "{" > String > ":" > JSON > *("," > String > ":" > JSON) > "}";
JSON = Object | Array | String | Number | Boolean | Null;
grammar_ = start(JSON);
