해요 : :
여기에서 찾고 하나 개의 링크 아마도 가치가 표시 될 수있는 정보의 양을 최적화.
다음은 Debuggex가 사용하는 파서에서 크게 수정 된 (미리보기 쉬운) 코드 단편입니다. 있는 그대로 작동하지는 않지만 코드 구성을 보여주기위한 것입니다. 대부분의 오류 처리가 제거되었습니다. 따라서 많은 논리들이 간단하지만 장황했다.
recursive descent이 사용됩니다. 이것은 파서에서 한 것입니다. 단 하나의 함수로 병합됩니다. 나는 나의 대략이 문법을 사용 :
Regex -> Alt
Alt -> Cat ('|' Cat)*
Cat -> Empty | (Repeat)+
Repeat -> Base (('*' | '+' | '?' | CustomRepeatAmount) '?'?)
Base -> '(' Alt ')' | Charset | Literal
Charset -> '[' (Char | Range | EscapeSeq)* ']'
Literal -> Char | EscapeSeq
CustomRepeatAmount -> '{' Number (',' Number)? '}'
당신은 그냥 정규 표현식에의 자바 스크립트 맛의 특수성에 대해 다루고 있습니다 내 코드를 많이 알 수 있습니다. 자세한 내용은 this reference에서 확인할 수 있습니다. PHP의 경우 this에 필요한 모든 정보가 있습니다. 나는 당신이 파서와 함께 잘 지내고 있다고 생각합니다. 남아있는 모든 것은 나머지 사업자를 구현하고 핵심 사례를 올바르게 구현하는 것입니다.
는 :) 즐기십시오 :
var Parser = function(s) {
this.s = s; // This is the regex string.
this.k = 0; // This is the index of the character being parsed.
this.group = 1; // This is a counter for assigning to capturing groups.
};
// These are convenience methods to make reading and maintaining the code
// easier.
// Returns true if there is more string left, false otherwise.
Parser.prototype.more = function() {
return this.k < this.s.length;
};
// Returns the char at the current index.
Parser.prototype.peek = function() { // exercise
};
// Returns the char at the current index, then advances the index.
Parser.prototype.next = function() { // exercise
};
// Ensures c is the char at the current index, then advances the index.
Parser.prototype.eat = function(c) { // exercise
};
// We use a recursive descent parser.
// This returns the root node of our tree.
Parser.prototype.parseRe = function() {
// It has exactly one child.
return new ReTree(this.parseAlt());
// We expect that to be at the end of the string when we finish parsing.
// If not, something went wrong.
if (this.more()) {
throw new Error();
}
};
// This parses several subexpressions divided by |s, and returns a tree
// with the corresponding trees as children.
Parser.prototype.parseAlt = function() {
var alts = [this.parseCat()];
// Keep parsing as long as a we have more pipes.
while (this.more() && this.peek() === '|') {
this.next();
// Recursive descent happens here.
alts.push(this.parseCat());
}
// Here, we allow an AltTree with single children.
// Alternatively, we can return the child if there is only one.
return new AltTree(alts);
};
// This parses several concatenated repeat-subexpressions, and returns
// a tree with the corresponding trees as children.
Parser.prototype.parseCat = function() {
var cats = [];
// If we reach a pipe or close paren, we stop. This is because that
// means we are in a subexpression, and the subexpression is over.
while (this.more() && ')|'.indexOf(this.peek()) === -1) {
// Recursive descent happens here.
cats.push(this.parseRepeat());
}
// This is where we choose to handle the empty string case.
// It's easiest to handle it here because of the implicit concatenation
// operator in our grammar.
return (cats.length >= 1) ? new CatTree(cats) : new EmptyTree();
};
// This parses a single repeat-subexpression, and returns a tree
// with the child that is being repeated.
Parser.prototype.parseRepeat = function() {
// Recursive descent happens here.
var repeat = this.parseBase();
// If we reached the end after parsing the base expression, we just return
// it. Likewise if we don't have a repeat operator that follows.
if (!this.more() || '*?+{'.indexOf(this.peek()) === -1) {
return repeat;
}
// These are properties that vary with the different repeat operators.
// They aren't necessary for parsing, but are used to give meaning to
// what was parsed.
var min = 0; var max = Infinity; var greedy = true;
if (this.peek() === '*') { // exercise
} else if (this.peek() === '?') { // exercise
} else if (this.peek() === '+') {
// For +, we advance the index, and set the minimum to 1, because
// a + means we repeat the previous subexpression between 1 and infinity
// times.
this.next(); min = 1;
} else if (this.peek() === '{') { /* challenging exercise */ }
if (this.more() && this.peek() === '?') {
// By default (in Javascript at least), repetition is greedy. Appending
// a ? to a repeat operator makes it reluctant.
this.next(); greedy = false;
}
return new RepeatTree(repeat, {min:min, max:max, greedy:greedy});
};
// This parses a "base" subexpression. We defined this as being a
// literal, a character set, or a parnthesized subexpression.
Parser.prototype.parseBase = function() {
var c = this.peek();
// If any of these characters are spotted, something went wrong.
// The) should have been eaten by a previous call to parseBase().
// The *, ?, or + should have been eaten by a previous call to parseRepeat().
if (c === ')' || '*?+'.indexOf(c) !== -1) {
throw new Error();
}
if (c === '(') {
// Parse a parenthesized subexpression. This is either a lookahead,
// a capturing group, or a non-capturing group.
this.next(); // Eat the (.
var ret = null;
if (this.peek() === '?') { // excercise
// Parse lookaheads and non-capturing groups.
} else {
// This is why the group counter exists. We use it to enumerate the
// group appropriately.
var group = this.group++;
// Recursive descent happens here. Note that this calls parseAlt(),
// which is what was initially called by parseRe(), creating
// a mutual recursion. This is where the name recursive descent
// comes from.
ret = new MatchTree(this.parseAlt(), group);
}
// This MUST be a) or something went wrong.
this.eat(')');
return ret;
} else if (c === '[') {
this.next(); // Eat the [.
// Parse a charset. A CharsetTree has no children, but it does contain
// (pseudo)chars and ranges, and possibly a negation flag. These are
// collectively returned by parseCharset().
// This piece can be structured differently depending on your
// implementation of parseCharset()
var opts = this.parseCharset();
// This MUST be a ] or something went wrong.
this.eat(']');
return new CharsetTree(opts);
} else {
// Parse a literal. Like a CharsetTree, a LiteralTree doesn't have
// children. Instead, it contains a single (pseudo)char.
var literal = this.parseLiteral();
return new LiteralTree(literal);
}
};
// This parses the inside of a charset and returns all the information
// necessary to describe that charset. This includes the literals and
// ranges that are accepted, as well as whether the charset is negated.
Parser.prototype.parseCharset = function() {
// challenging exercise
};
// This parses a single (pseudo)char and returns it for use in a LiteralTree.
Parser.prototype.parseLiteral = function() {
var c = this.next();
if (c === '.' || c === '^' || c === '$') {
// These are special chars. Their meaning is different than their
// literal symbol, so we set the 'special' flag.
return new CharInfo(c, true);
} else if (c === '\\') {
// If we come across a \, we need to parse the escaped character.
// Since parsing escaped characters is similar between literals and
// charsets, we extracted it to a separate function. The reason we
// pass a flag is because \b has different meanings inside charsets
// vs outside them.
return this.parseEscaped({inCharset: false});
}
// If neither case above was hit, we just return the exact char.
return new CharInfo(c);
};
// This parses a single escaped (pseudo)char and returns it for use in
// either a LiteralTree or a CharsetTree.
Parser.prototype.parseEscaped = function(opts) {
// Here we instantiate some default options
opts = opts || {};
inCharset = opts.inCharset || false;
var c = peek();
// Here are a bunch of escape sequences that require reading further
// into the string. They are all fairly similar.
if (c === 'c') { // exercises
} else if (c === '0') {
} else if (isDigit(c)) {
} else if (c === 'x') {
} else if (c === 'u') {
// Use this as an example for implementing the ones above.
// A regex may be used for this portion, but I think this is clearer.
// We make sure that there are exactly four hexadecimal digits after
// the u. Modify this for the escape sequences that your regex flavor
// uses.
var r = '';
this.next();
for (var i = 0; i < 4; ++i) {
c = peek();
if (!isHexa(c)) {
throw new Error();
}
r += c;
this.next();
}
// Return a single CharInfo desite having read multiple characters.
// This is why I used "pseudo" previously.
return new CharInfo(String.fromCharCode(parseInt(r, 16)));
} else { // No special parsing required after the first escaped char.
this.next();
if (inCharset && c === 'b') {
// Within a charset, \b means backspace
return new CharInfo('\b');
} else if (!inCharset && (c === 'b' || c === 'B')) {
// Outside a charset, \b is a word boundary (and \B is the complement
// of that). We mark it one as special since the character is not
// to be taken literally.
return new CharInfo('\\' + c, true);
} else if (c === 'f') { // these are left as exercises
} else if (c === 'n') {
} else if (c === 'r') {
} else if (c === 't') {
} else if (c === 'v') {
} else if ('dDsSwW'.indexOf(c) !== -1) {
} else {
// If we got to here, the character after \ should be taken literally,
// so we don't mark it as special.
return new CharInfo(c);
}
}
};
// This represents the smallest meaningful character unit, or pseudochar.
// For example, an escaped sequence with multiple physical characters is
// exactly one character when used in CharInfo.
var CharInfo = function(c, special) {
this.c = c;
this.special = special || false;
};
// Calling this will return the parse tree for the regex string s.
var parse = function(s) { return (new Parser(s)).parseRe(); };
정규식을 사용해 보셨습니까? 오, 아니, 이미 12 가지 문제가 있습니다. O –
@Ivo : 사실, 처음 구현 한 것은 정규 표현식을 기반으로했지만 너무 복잡해져서 간단한 문자 기반 루프로 전환하지 않았습니다. –
당신은 이것을 http://xenon.stanford.edu/~xusch/regexp/analyzer.html 과 같이 구현하려고합니다. –