57e806383c
Using a special value to indicate match failure instead of |null| allows actions to return |null| as a regular value. This simplifies e.g. the JSON parser. Note the special value is internal and intentionally undocumented. This means that there is currently no official way how to trigger a match failure from an action. This is a temporary state which will be fixed soon. The negative performance impact (see below) is probably caused by changing lot of comparisons against |null| (which likely check the value against a fixed constant representing |null| in the interpreter) to comparisons against the special value (which likely check the value against another value in the interpreter). Implements part of #198. Speed impact ------------ Before: 1146.82 kB/s After: 1031.25 kB/s Difference: -10.08% Size impact ----------- Before: 950817 b After: 973269 b Difference: 2.36% (Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
120 lines
2.5 KiB
JavaScript
120 lines
2.5 KiB
JavaScript
/* JSON parser based on the grammar described at http://json.org/. */
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/* ===== Syntactical Elements ===== */
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start
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= _ object:object { return object; }
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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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pair
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= name:string ":" _ value:value { return [name, value]; }
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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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value
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= string
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/ number
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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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chars
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= chars:char+ { return chars.join(""); }
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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:$(hexDigit hexDigit hexDigit hexDigit) {
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return String.fromCharCode(parseInt("0x" + digits));
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}
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number "number"
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= parts:$(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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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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frac
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= "." digits
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exp
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= e digits
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digits
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= digit+
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e
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= [eE] [+-]?
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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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digit
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= [0-9]
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digit19
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= [1-9]
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hexDigit
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= [0-9a-fA-F]
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/* ===== Whitespace ===== */
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_ "whitespace"
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= whitespace*
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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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