Complete rewrite of the JSON example grammar
This is a complete rewrite of the JSON example grammar. It is now based on RFC 7159 instead of an informal description at the JSON website. Beside this, the rewrite reflects how I write grammars today (as opposed to few years ago) and what style I would recommend to others.redux
David Majda
11 years ago
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/* JSON parser based on the grammar described at http://json.org/. */
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/*
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* JSON Grammar
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* ============
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*
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* Based on the grammar from RFC 7159 [1].
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*
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* Note that JSON is also specified in ECMA-262 [2], ECMA-404 [3], and on the
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* JSON website [4] (somewhat informally). The RFC seems the most authoritative
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* source, which is confirmed e.g. by [5].
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*
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* [1] http://tools.ietf.org/html/rfc7159
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* [2] http://www.ecma-international.org/publications/standards/Ecma-262.htm
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* [3] http://www.ecma-international.org/publications/standards/Ecma-404.htm
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* [4] http://json.org/
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* [5] https://www.tbray.org/ongoing/When/201x/2014/03/05/RFC7159-JSON
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*/
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/* ===== Syntactical Elements ===== */
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/* ----- 2. JSON Grammar ----- */
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start
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= _ object:object { return object; }
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JSON_text
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= ws value:value ws { return value; }
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object
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= "{" _ "}" _ { return {}; }
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/ "{" _ members:members "}" _ { return members; }
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members
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= head:pair tail:("," _ pair)* {
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var result = {};
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result[head[0]] = head[1];
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for (var i = 0; i < tail.length; i++) {
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result[tail[i][2][0]] = tail[i][2][1];
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}
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return result;
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}
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begin_array = ws "[" ws
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begin_object = ws "{" ws
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end_array = ws "]" ws
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end_object = ws "}" ws
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name_separator = ws ":" ws
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value_separator = ws "," ws
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pair
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= name:string ":" _ value:value { return [name, value]; }
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ws "whitespace" = [ \t\n\r]*
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array
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= "[" _ "]" _ { return []; }
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/ "[" _ elements:elements "]" _ { return elements; }
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elements
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= head:value tail:("," _ value)* {
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var result = [head];
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for (var i = 0; i < tail.length; i++) {
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result.push(tail[i][2]);
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}
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return result;
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}
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/* ----- 3. Values ----- */
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value
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= string
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/ number
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= false
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/ null
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/ true
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/ object
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/ array
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/ "true" _ { return true; }
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/ "false" _ { return false; }
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/ "null" _ { return null; }
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/* ===== Lexical Elements ===== */
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string "string"
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= '"' '"' _ { return ""; }
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/ '"' chars:chars '"' _ { return chars; }
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/ number
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/ string
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chars
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= chars:char+ { return chars.join(""); }
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false = "false" { return false; }
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null = "null" { return null; }
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true = "true" { return true; }
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char
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// In the original JSON grammar: "any-Unicode-character-except-"-or-\-or-control-character"
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= [^"\\\0-\x1F\x7f]
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/ '\\"' { return '"'; }
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/ "\\\\" { return "\\"; }
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/ "\\/" { return "/"; }
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/ "\\b" { return "\b"; }
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/ "\\f" { return "\f"; }
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/ "\\n" { return "\n"; }
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/ "\\r" { return "\r"; }
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/ "\\t" { return "\t"; }
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/ "\\u" digits:$(hexDigit hexDigit hexDigit hexDigit) {
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return String.fromCharCode(parseInt(digits, 16));
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}
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/* ----- 4. Objects ----- */
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number "number"
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= parts:$(int frac exp) _ { return parseFloat(parts); }
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/ parts:$(int frac) _ { return parseFloat(parts); }
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/ parts:$(int exp) _ { return parseFloat(parts); }
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/ parts:$(int) _ { return parseFloat(parts); }
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object
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= begin_object
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members:(
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first:member
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rest:(value_separator m:member { return m; })*
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{
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var result = {}, i;
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int
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= digit19 digits
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/ digit
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/ "-" digit19 digits
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/ "-" digit
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result[first.name] = first.value;
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frac
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= "." digits
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for (i = 0; i < rest.length; i++) {
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result[rest[i].name] = rest[i].value;
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}
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exp
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= e digits
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return result;
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}
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)?
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end_object
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{ return members !== null ? members: {}; }
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digits
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= digit+
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member
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= name:string name_separator value:value {
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return { name: name, value: value };
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}
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e
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= [eE] [+-]?
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/* ----- 5. Arrays ----- */
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/*
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* The following rules are not present in the original JSON gramar, but they are
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* assumed to exist implicitly.
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*
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* FIXME: Define them according to ECMA-262, 5th ed.
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*/
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array
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= begin_array
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values:(
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first:value
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rest:(value_separator v:value { return v; })*
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{ return [first].concat(rest); }
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)?
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end_array
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{ return values !== null ? values : []; }
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digit
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= [0-9]
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/* ----- 6. Numbers ----- */
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digit19
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= [1-9]
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number "number"
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= minus? int frac? exp? { return parseFloat(text()); }
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hexDigit
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= [0-9a-fA-F]
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decimal_point = "."
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digit1_9 = [1-9]
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e = [eE]
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exp = e (minus / plus)? DIGIT+
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frac = decimal_point DIGIT+
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int = zero / (digit1_9 DIGIT*)
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minus = "-"
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plus = "+"
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zero = "0"
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/* ===== Whitespace ===== */
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/* ----- 7. Strings ----- */
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_ "whitespace"
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= whitespace*
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string "string"
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= quotation_mark chars:char* quotation_mark { return chars.join(""); }
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// Whitespace is undefined in the original JSON grammar, so I assume a simple
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// conventional definition consistent with ECMA-262, 5th ed.
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whitespace
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= [ \t\n\r]
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char
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= unescaped
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/ escape
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sequence:(
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'"'
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/ "\\"
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/ "/"
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/ "b" { return "\b"; }
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/ "f" { return "\f"; }
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/ "n" { return "\n"; }
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/ "r" { return "\r"; }
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/ "t" { return "\t"; }
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/ "u" digits:$(HEXDIG HEXDIG HEXDIG HEXDIG) {
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return String.fromCharCode(parseInt(digits, 16));
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}
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)
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{ return sequence; }
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escape = "\\"
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quotation_mark = '"'
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unescaped = [\x20-\x21\x23-\x5B\x5D-\u10FFFF]
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/* ----- Core ABNF Rules ----- */
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/* See RFC 4234, Appendix B (http://tools.ietf.org/html/rfc4627). */
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DIGIT = [0-9]
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HEXDIG = [0-9a-f]i
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