fastparse

A very simple and stupid parser, based on a statemachine and regular expressions.

fastparse

A very simple and stupid parser, based on a statemachine and regular expressions.

It's not intended for complex languages. It's intended to easily write a simple parser for a simple language.

Pass a description of statemachine to the constructor. The description must be in this form:

new Parser(description)
 
description is {
// The key is the name of the state 
// The value is an object containing possible transitions 
"state-name": {
// The key is a regular expression 
// If the regular expression matches the transition is executed 
// The value can be "true", a other state name or a function 
 
"a": true,
// true will make the parser stay in the current state 
"b": "other-state-name",
// a string will make the parser transit to a new state 
"[cde]"function(matchindexmatchLength) {
// "match" will be the matched string 
// "index" will be the position in the complete string 
// "matchLength" will be "match.length" 
// "this" will be the "context" passed to the "parse" method" 
// A new state name (string) can be returned 
return "other-state-name";
},
"([0-9]+)(\\.[0-9]+)?"function(matchfirstsecondindexmatchLength) {
// groups can be used in the regular expression 
// they will match to arguments "first", "second" 
},
// the parser stops when it cannot match the string anymore 
// order of keys is the order in which regular expressions are matched 
// if the javascript runtime preserves the order of keys in an object 
// (this is not standardized, but it's a de-facto standard) 
}
}

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.

Parser.prototype.parse(initialState: String, parsedString: String, context: Object)

initialState: state where the parser starts to parse.

parsedString: the string which should be parsed.

context: an object which can be used to save state and results. Available as this in transition functions.

returns context

var Parser = require("fastparse");
 
// A simple parser that extracts @licence ... from comments in a JS file 
var parser = new Parser({
// The "source" state 
"source": {
// matches comment start 
"/\\*": "comment",
"//": "linecomment",
// this would be necessary for a complex language like JS 
// but omitted here for simplicity 
// "\"": "string1", 
// "\'": "string2", 
// "\/": "regexp" 
},
// The "comment" state 
"comment": {
"\\*/": "source",
"@licen[cs]e\\s((?:[^*\n]|\\*+[^*/\n])*)"function(matchlicenseText) {
this.licences.push(licenseText.trim());
}
},
// The "linecomment" state 
"linecomment": {
"\n": "source",
"@licen[cs]e\\s(.*)"function(matchlicenseText) {
this.licences.push(licenseText.trim());
}
}
});
 
var licences = parser.parse("source", sourceCode, { licences: [] }).licences;
 
console.log(licences);

MIT (http://www.opensource.org/licenses/mit-license.php)