A small tool for calculating first, follow and predict sets for the grammar. Its size is only 564 bytes (minified and gzipped). No dependencies. Size Limit controls the size.
$ npm install first-follow
You can try this tool here.
const firstFollow = require('first-follow');
const rules = [
// S -> a b A
{
left: 'S',
right: ['a', 'b', 'A']
},
// A -> b c
{
left: 'A',
right: ['b', 'c']
},
// A -> ε
{
left: 'A',
right: [null]
}
];
const { firstSets, followSets, predictSets } = firstFollow(rules);
console.log(firstSets);
/*
* // S: a
* // A: b, ε
*
* {
* S: ['a'],
* A: ['b', null]
* }
*/
console.log(followSets);
/*
* // S: ┤
* // A: ┤
*
* {
* S: ['\u0000'],
* A: ['\u0000']
* }
*/
console.log(predictSets);
/*
* // 1: a
* // 2: b
* // 3: ┤
*
* {
* '1': ['a'],
* '2': ['b'],
* '3': ['\u0000']
* }
*/
The grammar is represented by array of objects. Each object describes the only one rule. The rule's object contains two required fields:
left
— specifies the left part of the rule. A single nonterminal:A
,B
,Program
,Expression
, etc.right
— specifies the right part of the rule. It contains terminals and nonterminals or empty chain (epsilon):A + B
,d * A
,ε
, etc.
- The
firstSets
object's keys are nonterminals and values are first sets for these nonterminals. - The
followSets
object's keys are nonterminals and values are follow sets for these nonterminals. - The
predictSets
object's keys are rules numbers (starting from1
) and values are predict sets for these rules.
- An empty chain (
ε
) is represented bynull
. - An end mark (
┤
) is represented by\u0000
.