First and Follow set Solver

First and follow set solver in Javascript. This library can be used to help you write your Parsers. It is currently being used to auto generate a parser based on the rule set.

Demo

To see this library in action check out this cool tool

How to add the library to your project?

1. Using npm npm install first-follow-solver followed by import { solve } from 'first-follow-solver'

2. Or you can compile the library by running npm run-script build and then adding the dist/first-follow-solver.js to your html directly: <script src="./dist/first-follow-solver.js"></script>

How to use the library?

let problem = {
	rules: [
		{lhs: "S", rhs: ["a", "b"]}, // S -> a b
		{lhs: "S", rhs: ["b", "b"]}, // S -> b b
		{lhs: "S", rhs: ["b"]} //  S -> b
	],
	// if not specified all symbols 
	// not used on the left side will be assumed to be terminals
	terminals: ["a", "b"], 
	start: "S", // S is a default value
	epsilon: "epsilon", // epsilon is the default value
	eof: "$", // $ is the default value
}

If included from the first-follow-solver.js file:

console.log("Solution", FirstFollowSolver.solve(problem));

If included using npm:

console.log("Solution", solve(problem));

Full API

solve(config)
validateSymbols(rules, terminals, epsilon)
extractTerminals(rules, mode, epsilon)
parseProgram(text, split)

solve (method)

Parameters

• config the configuration object
  • config.rules an array of rules
    • config.rules.0.lhs an object representing the head of the rule (left hand side)
    • config.rules.0.rhs an array of strings representing the right hand side symbols
  • config.terminals an array of string in which every string is a terminal
  • config.start string that represents the non terminal which starts the program
  • config.epsilon string that represents the epsilon symbol
  • config.eof string that represents the end of file symbol (used for follow sets)

Examples

let problem = {
	rules: [
		{lhs: "S", rhs: ["a", "b"]}, // S -> a b
		{lhs: "S", rhs: ["b", "b"]}, // S -> b b
		{lhs: "S", rhs: ["b"]} //  S -> b
	],
	// if not specified all symbols 
	// not used on the left side will be assumed to be terminals
	terminals: ["a", "b"], 
	start: "S", // S is a default value
	epsilon: "epsilon", // epsilon is the default value
	eof: "$", // $ is the default value
}

console.log("Solution", FirstFollowSolver.solve(problem));

// result is {"firstSet":{"S":["a","b"]},"followSet":{"S":["$"]}}

validateSymbols (method)

Parameters

• rules an array of rules
  • rules.0.lhs an object representing the head of the rule (left hand side)
  • rules.0.rhs an array of strings representing the right hand side symbols
• terminals an array of strings, each string is a terminal
• epsilon string that represents the epsilon symbol

Exceptions

• Throws an exception that is a string containing the error if either one of the rules is broken

terminals cannot be on the left hand side

non terminals must be on the left hand side

Examples

let rules = [
		{lhs: "S", rhs: ["a", "b"]}, // S -> a b
		{lhs: "S", rhs: ["b", "b"]}, // S -> b b
		{lhs: "S", rhs: ["b"]} //  S -> b
];
let terminals = ["a", "b"];
let epsilon = "epsilon";

FirstFollowSolver.validateSymbols(rules, terminals, epsilon);

extractTerminals (method)

Parameters

• rules an array of rules
  • rules.0.lhs an object representing the head of the rule (left hand side)
  • rules.0.rhs an array of strings representing the right hand side symbols
• mode a string that represents how the values are to be extracted
  • "lowercase" symbols are extracted as terminals if they contain a lowercase char
  • "notLhs" symbols are extracted as terminals if they are not rule heads (left hand side)
• epsilon string that represents the epsilon symbol

Examples

let rules = [
		{lhs: "S", rhs: ["a", "b"]}, // S -> a b
		{lhs: "S", rhs: ["b", "b"]}, // S -> b b
		{lhs: "S", rhs: ["b"]} //  S -> b
];
let mode = "lowercase";
let epsilon = "epsilon";

console.log("Terminals", FirstFollowSolver.extractTerminals(rules, mode, epsilon));
// result is [a, b]

parseProgram (method)

Parameters

• text the full program defined as a string, rules are separated into new lines
• split the string used to separate mutliple single line rules. Example S -> A | B

Examples

let grammarAsStr = "S -> demo | epsilon";
let split = "|";

console.log("Rules", FirstFollowSolver.parseProgram(grammarAsStr, split));
// result is [{lhs: "S", rhs: ["demo", "epsilon"]}]

Feel free to contact me at email me at [email protected]