forked from zhurui/management
119 lines
3.1 KiB
Markdown
119 lines
3.1 KiB
Markdown
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# fastparse
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A very simple and stupid parser, based on a statemachine and regular expressions.
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It's not intended for complex languages. It's intended to easily write a simple parser for a simple language.
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## Usage
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Pass a description of statemachine to the constructor. The description must be in this form:
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``` javascript
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new Parser(description)
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description is {
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// The key is the name of the state
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// The value is an object containing possible transitions
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"state-name": {
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// The key is a regular expression
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// If the regular expression matches the transition is executed
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// The value can be "true", a other state name or a function
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"a": true,
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// true will make the parser stay in the current state
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"b": "other-state-name",
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// a string will make the parser transit to a new state
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"[cde]": function(match, index, matchLength) {
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// "match" will be the matched string
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// "index" will be the position in the complete string
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// "matchLength" will be "match.length"
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// "this" will be the "context" passed to the "parse" method"
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// A new state name (string) can be returned
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return "other-state-name";
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},
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"([0-9]+)(\\.[0-9]+)?": function(match, first, second, index, matchLength) {
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// groups can be used in the regular expression
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// they will match to arguments "first", "second"
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},
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// the parser stops when it cannot match the string anymore
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// order of keys is the order in which regular expressions are matched
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// if the javascript runtime preserves the order of keys in an object
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// (this is not standardized, but it's a de-facto standard)
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}
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}
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```
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The statemachine is compiled down to a single regular expression per state. So basically the parsing work is delegated to the (native) regular expression logic of the javascript runtime.
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``` javascript
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Parser.prototype.parse(initialState: String, parsedString: String, context: Object)
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```
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`initialState`: state where the parser starts to parse.
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`parsedString`: the string which should be parsed.
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`context`: an object which can be used to save state and results. Available as `this` in transition functions.
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returns `context`
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## Example
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``` javascript
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var Parser = require("fastparse");
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// A simple parser that extracts @licence ... from comments in a JS file
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var parser = new Parser({
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// The "source" state
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"source": {
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// matches comment start
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"/\\*": "comment",
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"//": "linecomment",
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// this would be necessary for a complex language like JS
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// but omitted here for simplicity
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// "\"": "string1",
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// "\'": "string2",
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// "\/": "regexp"
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},
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// The "comment" state
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"comment": {
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"\\*/": "source",
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"@licen[cs]e\\s((?:[^*\n]|\\*+[^*/\n])*)": function(match, licenseText) {
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this.licences.push(licenseText.trim());
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}
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},
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// The "linecomment" state
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"linecomment": {
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"\n": "source",
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"@licen[cs]e\\s(.*)": function(match, licenseText) {
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this.licences.push(licenseText.trim());
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}
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}
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});
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var licences = parser.parse("source", sourceCode, { licences: [] }).licences;
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console.log(licences);
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```
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## License
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MIT (http://www.opensource.org/licenses/mit-license.php)
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