Reimplement RegExp in JavaScript

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RegExp. exec(‘js’) @jviereck JSConf.EU 2013

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/a/ /.?/ /(foo|bar)+/ /(^.*a)+/ /([a-zA-Z]\s\d)+/ /jsconf\.eu/ /^abc$/ /(?=Hello)\sWorld/ /.*?/ /[^]/

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/a/ /.?/ /(foo|bar)+/ /(^.*a)+/ /([a-zA-Z]\s\d)+/ /jsconf\.eu/ /^abc$/ /(?=Hello)\sWorld/ /.*?/ /[^]/ They look cute

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/a/ /.?/ /(foo|bar)+/ /(^.*a)+/ /([a-zA-Z]\s\d)+/ /jsconf\.eu/ /^abc$/ /(?=Hello)\sWorld/ /.*?/ /[^]/ They look cute But they are hard to get right :(

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“Why are you doing this?”

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Motivation • Debug-ability • Writing JIT compiler • Wanted to present at JSConf.EU :)

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Demo http://jviereck.github.io/regexp.js/

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Overview • ParseTree • NodeList • Matcher • RegExpJS object itself • Writing a JIT in a JIT • Conclusion

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ParseTree 4

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ParseTree • ParseTree: • structural representation of a string • described by grammar rules • Highlevel: • RegExp =[Parser]=> ParseTree

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Example: /(ab|c)/ ParseTree

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Example: /(ab|c)/ ParseTree Group

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Disjunction Example: /(ab|c)/ ParseTree Group

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Alternative Disjunction Example: /(ab|c)/ ParseTree Group

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Char: “a” Term Alternative Disjunction Example: /(ab|c)/ ParseTree Group

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Char: “b” Term Char: “a” Term Alternative Disjunction Example: /(ab|c)/ ParseTree Group

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Char: “b” Term Char: “a” Term Alternative Alternative Disjunction Example: /(ab|c)/ ParseTree Group

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Char: “c” Term Char: “b” Term Char: “a” Term Alternative Alternative Disjunction Example: /(ab|c)/ ParseTree Group

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Parser • Handwritten - LL(?) • Only basic error handling/messages • Uses RegExp iteself << replace them ;) • Emits “useful” information

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Useful information { "type": "ref", "ref": 1, "from": 5, "to": 7, "raw": "\\1" } (a|b)\1

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/[a-]/.exec(‘-’): ✓

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/[a-]/.exec(‘-’): ✓ /[a-b]/.exec(‘-’): ✗

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Notes on parsing • Should have gone with parser generator? • Mostly follows the spec • Addition: added handling for /]/ • Parsing numbers needs an extra slide...

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Number parsing

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Number parsing • parseDecimalEscape(...)

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Number parsing • parseDecimalEscape(...) • /(a)(b)\2/ ‏ reference

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Number parsing • parseDecimalEscape(...) • /(a)(b)\2/ ‏ reference • /(a)(b)\71/ ‏ NOT reference

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Number parsing • parseDecimalEscape(...) • /(a)(b)\2/ ‏ reference • /(a)(b)\71/ ‏ NOT reference • IF: octal number, parseInt(71,8)

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Number parsing • parseDecimalEscape(...) • /(a)(b)\2/ ‏ reference • /(a)(b)\71/ ‏ NOT reference • IF: octal number, parseInt(71,8) • /(a)(b)\91/ ‏ NOT reference

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Number parsing • parseDecimalEscape(...) • /(a)(b)\2/ ‏ reference • /(a)(b)\71/ ‏ NOT reference • IF: octal number, parseInt(71,8) • /(a)(b)\91/ ‏ NOT reference • ELSE: Ignore slash, match /91/

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NodeList 8

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• ParseTree ➡ NodeList • Data structure Matcher uses NodeList

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• ParseTree ➡ NodeList • Data structure Matcher uses NodeList Example: /ab/

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• ParseTree ➡ NodeList • Data structure Matcher uses NodeList Data: “a” CHAR Example: /ab/

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CHAR Data: “b” • ParseTree ➡ NodeList • Data structure Matcher uses NodeList Data: “a” CHAR Example: /ab/

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DONE CHAR Data: “b” • ParseTree ➡ NodeList • Data structure Matcher uses NodeList Data: “a” CHAR Example: /ab/

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Example: /(ab|c)*c/

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Example: /(ab|c)*c/ Id: 1 Min: 0 Max: ? REPEAT

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Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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ALTR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Data: “a” CHAR ALTR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Data: “b” CHAR Data: “a” CHAR ALTR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Data: “b” CHAR Data: “a” CHAR CHAR Data: “c” ALTR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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JOIN Data: “b” CHAR Data: “a” CHAR CHAR Data: “c” ALTR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Index: 1 END_GROUP JOIN Data: “b” CHAR Data: “a” CHAR CHAR Data: “c” ALTR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Index: 1 END_GROUP JOIN Data: “b” CHAR Data: “a” CHAR CHAR Data: “c” ALTR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Index: 1 END_GROUP JOIN Data: “b” CHAR Data: “a” CHAR CHAR Data: “c” ALTR Data: “c” CHAR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Index: 1 END_GROUP JOIN Data: “b” CHAR Data: “a” CHAR CHAR Data: “c” ALTR DONE Data: “c” CHAR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT

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Index: 1 END_GROUP JOIN Data: “b” CHAR Data: “a” CHAR CHAR Data: “c” ALTR DONE Data: “c” CHAR Example: /(ab|c)*c/ Index: 1 BEGIN_GROUP Id: 1 Min: 0 Max: ? REPEAT Char: “c” Term Char: “b” Term Char: “a” Term Alternative Alternative Disjunction Group

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NodeList • Look complicated to build • Easy by walking over ParseTree • Combine one node after the other

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NodeList: \s

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NodeList: \s • \s: matches whitespace OR line terminator

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NodeList: \s • \s: matches whitespace OR line terminator • stolen functions from Esprima :)

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Matcher 12

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Matcher • Does the actual RegExp matching • Matcher(state, nodeList) • state = { string, index, traces, counters, ...} • Tries all possibilities till match OR no progress • Calls Matcher(state’, nodeList’) recursively • If trace fails ➠ return function = backtracking

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Matcher

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Matcher • s = new State(‘abc’)

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/)

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) a b c d a b d ^

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ a b c d a b d ^

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ a b c d a b d ^

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) a b c d a b d ^

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) a b c d a b d ^ “ s’=s.clone()

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) a b c d a b d ^ “ s’=s.clone()

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) • test(‘b’, /b/): ✓ a b c d a b d ^ “ s’=s.clone()

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) • test(‘b’, /b/): ✓ a b c d a b d ^ “ s’=s.clone()

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) • test(‘b’, /b/): ✓ a b c d a b d ^ “ s’=s.clone()

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) • test(‘b’, /b/): ✓ • test(‘d’, /d/): ✓ a b c d a b d ^ “ s’=s.clone()

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Matcher • s = new State(‘abc’) • match(s, /a(b|c)d/) • test(s, /a/): ✓ • try /b/: match(s’, /(b|c)d/) • test(‘b’, /b/): ✓ • test(‘d’, /d/): ✓ • DONE: ✓ a b c d a b d ^ “ s’=s.clone()

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• s = new State(‘abc’);

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• s = new State(‘abc’); • match(s, /a(b|c)d/) a c d ^ a b c d

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• s = new State(‘abc’); • match(s, /a(b|c)d/) a c d ^ a b c d

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ a c d ^ a b c d

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ a c d ^ a b c d

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) a c d ^ a b c d

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) a c d ^ a b c d “ s’=s.clone()

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) • test(s’, /b/): ✗ a c d ^ a b c d “ s’=s.clone()

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) • test(s’, /b/): ✗ ‏ Backtrack a c d ^ a b c d “ s’=s.clone()

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) • test(s’, /b/): ✗ ‏ Backtrack a c d ^ a b c d “ s’=s.clone()

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) • test(s’, /b/): ✗ ‏ Backtrack • try /c/: match(s’’, /(b|c)d/) a c d ^ a b c d “ s’=s.clone()

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) • test(s’, /b/): ✗ ‏ Backtrack • try /c/: match(s’’, /(b|c)d/) • test(‘c’, /c/): ✓ a c d ^ a b c d “ s’=s.clone()

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• s = new State(‘abc’); • match(s, /a(b|c)d/) • test(‘a’, /a/): ✓ • try /b/: match(s’, /bd/) • test(s’, /b/): ✗ ‏ Backtrack • try /c/: match(s’’, /(b|c)d/) • test(‘c’, /c/): ✓ • test(‘d’, /d/): ✓ a c d ^ a b c d “ s’=s.clone()

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Matcher pitfalls • /(a(b)*c)*/ • need to reset the matches of (b)* to null • also need to reset repeat counter • /()*a/ • Inﬁnity matches ➡ Loop detection!

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RegExpJS Object 16

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re = new RegExpJS(‘abc’, ‘ig’); re.exec(‘abc’) re.test(‘abc’) Sorry, nothing on the String.prototype...

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RegExpJS Object • So far: • created ParseTree • created NodeList • have Matcher(string, parseNodes) • Needed: • something to play with :) • actual JS object similar to RegExp object

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RegExpJS Object • ﬁrst attempt: • RegExpJS(regExp).exec = (str) => { regExp = this.regExp; nodes = buildNodeList(parse(regExp)); return match(str, nodes); } • RegExpJS(/abc/).exec(‘abc’): ✓ • RegExpJS(/abc/).exec(‘JSConf abc’): ✗

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Match arbitrary start position

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Match arbitrary start position • easy ﬁx:

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Match arbitrary start position • easy ﬁx: • wrap the nodeList by “fake loop”

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Match arbitrary start position • easy ﬁx: • wrap the nodeList by “fake loop” • e.g: /abc/

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Match arbitrary start position • easy ﬁx: • wrap the nodeList by “fake loop” • e.g: /abc/ • /abc/ ➠ /[^]*?(abc)/

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Match arbitrary start position • easy ﬁx: • wrap the nodeList by “fake loop” • e.g: /abc/ • /abc/ ➠ /[^]*?(abc)/ • assign the ﬁrst group index 0

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Match arbitrary start position • easy ﬁx: • wrap the nodeList by “fake loop” • e.g: /abc/ • /abc/ ➠ /[^]*?(abc)/ • assign the ﬁrst group index 0 • /abc/.exec(‘JSConf abc’): ✓

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Match arbitrary start position • easy ﬁx: • wrap the nodeList by “fake loop” • e.g: /abc/ • /abc/ ➠ /[^]*?(abc)/ • assign the ﬁrst group index 0 • /abc/.exec(‘JSConf abc’): ✓ • problem: V8 stack size not large enough

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How about ﬂags?

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How about ﬂags? •multiline ﬂag: /foo/m

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How about ﬂags? •multiline ﬂag: /foo/m • affects only /^/ and /$/ • easy to implement

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How about flags? •multiline flag: /foo/m • affects only /^/ and /$/ • easy to implement •global flag: /foo/g

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How about flags? •multiline flag: /foo/m • affects only /^/ and /$/ • easy to implement •global flag: /foo/g • repeat from last position • okay’isch to implement

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How about ﬂags? •ignore-case ﬂag: /foo/i • not just str.toUpperCase() • e.g. if turns one character into two, then use the input character • fun with ranges: • /[a-}]/ ➠ /[a-}A-Z]/

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More fun

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More fun • Spec requirement: • Call `ToString(...)`, `ToNumber(...)` on input • E.g. • str = { toString: function() { return false; } } • /LS/i.exec(str) ➡ returns?

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More fun • Spec requirement: • Call `ToString(...)`, `ToNumber(...)` on input • E.g. • str = { toString: function() { return false; } } • /LS/i.exec(str) ➡ returns? • /LS/i.exec(str) === “ls”

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so, RegExpJS object • There is more “fun” stuff required to get the ECMA test suite to pass • index.js (implements RegExpJS) ~240 LOC

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JIT (just in time compiler) 20

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JIT (just in time compiler) :) :) :) 20

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JIT Overview • Convert RegExp ➡ JS-Code • Have a RegExp-JIT running in JS-JIT • Idea: match input faster • use state machine / ﬁnite automata • only support a subset of RegExp • ... but these very fast & efﬁcient

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Supported features • All features, except: • groups matches, lookahead - only (?: ) • no backreferences • only greedy repetitions • Not supported yet • repetitions, ... (under construction) • (written in three evenings hacks ;) )

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this.name = id + ': NFA-States={' + nfaStates.map(function(state) {return state.name}).join(', ') + '} '; I really mean three hack evenings!

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RegExp:

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RegExp: /ab/

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RegExp: /ab/ NFA:

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RegExp: /ab/ NFA: 0 1 4 a b 2 ε

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RegExp: NFA: 0 1 4 a b 2 ε

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RegExp: NFA: 0 1 4 a b 2 ε /ab|a/

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RegExp: NFA: 0 1 4 a b 2 ε 3 a ε /ab|a/

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RegExp: NFA: 0 1 4 a b 2 ε 3 a ε DFA: /ab|a/

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RegExp: NFA: 0 1 4 a b 2 ε 3 a ε DFA: 0 1 a b 2 /ab|a/

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JIT Implementation • Convert RegExp to state machine • RegExp • Non-deterministic Finite Automata (NFA) • Deterministic Finite Automata (DFA) • CodeGen ➠ JavaScript code

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/ab/ 0 1 2 a b 23

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alphabet: Σ={a, b} /ab/ 0 1 2 a b 23

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What alphabet to use?

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What alphabet to use? • e.g.: ranges like /[a-\u0777]/

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What alphabet to use? • e.g.: ranges like /[a-\u0777]/ • use one transition per character

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What alphabet to use? • e.g.: ranges like /[a-\u0777]/ • use one transition per character 0 1 a, b, c, ...

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What alphabet to use? • e.g.: ranges like /[a-\u0777]/ • use one transition per character • better solution? 0 1 a, b, c, ...

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Alphabet Classes

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Alphabet Classes • Example: /0[1-9]/

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Alphabet Classes • Example: /0[1-9]/ 0 1 2 0 1...9

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Alphabet Classes • Example: /0[1-9]/ 0 1 2 0 1...9 alphabet: Σ={0, 1, 2, ..., 9}

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Alphabet Classes • Example: /0[1-9]/ • before /ab/ 0 1 2 0 1...9 alphabet: Σ={0, 1, 2, ..., 9}

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Alphabet Classes • Example: /0[1-9]/ • before /ab/ 0 1 2 a b 0 1 2 0 1...9 alphabet: Σ={0, 1, 2, ..., 9}

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Alphabet Classes • Example: /0[1-9]/ • before /ab/ • let 0 1 2 a b 0 1 2 0 1...9 alphabet: Σ={0, 1, 2, ..., 9}

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Alphabet Classes • Example: /0[1-9]/ • before /ab/ • let • a ≐ 0 0 1 2 a b 0 1 2 0 1...9 alphabet: Σ={0, 1, 2, ..., 9}

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Alphabet Classes • Example: /0[1-9]/ • before /ab/ • let • a ≐ 0 • b ≐ 1...9 0 1 2 a b 0 1 2 0 1...9 alphabet: Σ={0, 1, 2, ..., 9}

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Alphabet Classes • Example: /0[1-9]/ • before /ab/ • let • a ≐ 0 • b ≐ 1...9 0 1 2 a b 0 1 2 0 1...9 alphabet: Σ={0, 1, 2, ..., 9} alphabet: Σ={a, b}

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Alphabet Classes Calculation 0 numberline

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Alphabet Classes Calculation A ≐ 65 0 numberline

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Alphabet Classes Calculation A ≐ 65 Z ≐ 90 0 numberline

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Alphabet Classes Calculation A-E /[A-E]/ A ≐ 65 Z ≐ 90 0 numberline

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Alphabet Classes Calculation A-E /[A-E]/ C-Z /[C-Z]/ A ≐ 65 Z ≐ 90 0 numberline

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Alphabet Classes Calculation A-E /[A-E]/ C-Z /[C-Z]/ A ≐ 65 Z ≐ 90 0 numberline

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Alphabet Classes Calculation A-E /[A-E]/ C-Z /[C-Z]/ A-C D-E F-Z A ≐ 65 Z ≐ 90 0 numberline

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Alphabet Classes Calculation A-E /[A-E]/ C-Z /[C-Z]/ A-C D-E F-Z ≐ a ≐ b ≐ c A ≐ 65 Z ≐ 90 0 numberline

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RegExp: /[A-E]|[C-Z]/

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RegExp: /[A-E]|[C-Z]/ 0 1 2 3 A...E C...Z ε ε

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RegExp: /[A-E]|[C-Z]/ 0 1 2 3 A...E C...Z ε ε 0 1 2 3 a, b b, c ε ε

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How JITy is the JIT code?

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“Well, branchy. Not good”

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Closing Up 26

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TODO • Code cleanup • JIT still under construction • Align Parser/Traversal API with Esprima’s

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Status • Matcher works agains all test cases • Help needed: • project page • bugﬁxes • tester!

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More important • Crazy ideas what to use this for :) • Esprima enabled many analysis tools • Hope RegExp.JS becomes used as well • Lint RegExp • Monitor RegExp execution