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:
newParser(description)descriptionis{// 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(match,index,matchLength){// "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 returnedreturn"other-state-name";},"([0-9]+)(\\.[0-9]+)?": function(match,first,second,index,matchLength){// 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
varParser=require("fastparse");// A simple parser that extracts @licence ... from comments in a JS filevarparser=newParser({// 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(match,licenseText){this.licences.push(licenseText.trim());}},// The "linecomment" state"linecomment": {"\n": "source","@licen[cs]e\\s(.*)": function(match,licenseText){this.licences.push(licenseText.trim());}}});varlicences=parser.parse("source",sourceCode,{licences: []}).licences;console.log(licences);