Write a Program to Count The Number of Lexeme using JavaScript in Compiler Design

Write a Program to Count The Number of Lexeme using JavaScript in Compiler Design

In the field of compiler design, the identification and counting of lexemes are fundamental tasks in the lexical analysis phase. Lexemes are the building blocks of programming languages, consisting of sequences of alphanumeric characters within tokens. This article will explore how to write a program to count the number of lexemes in a given program using JavaScript. We will provide a theoretical overview of lexemes, present the code implementation, and discuss the input/output scenarios.

What is Lexeme?

A lexeme represents a meaningful sequence of characters that forms a part of a token. 

In the context of computer programming, lexemes are extracted from the input stream during lexical analysis to identify tokens. 

Each lexeme plays a crucial role in the overall syntax and semantics of a programming language. 

Understanding and counting lexemes is essential for accurately analyzing and processing programs.

Program to Count The Number of Lexeme in JavaScript:

Let's dive into the code that counts the number of lexemes using JavaScript:

let countKeywords = 0;
let countIdentifierConstant = 0;
let countSeparators = 0;

// Array of keywords
let keywords = ["auto","double","int","struct","break","else","long",

// Input expression
let expression = "if(float(b) + double(c) == 9text--) { char(ABC+++)}";

// Array of separators
let separators = ["==","=",",","++","+","--","-","*","/","%","{","}","(",")","<",">","[","]"];

function hasSeparators(separators) {
    for (let newline of expression) {
        for (let separator of separators) {
            if (expression.includes(separator)) {
                expression = expression.replace(`${separator}`, ' ');
    return expression;

function detectKeyword(keywords, newExpression) {
    let resultKeywords = [];
    for (let expression of newExpression) {
        for (let keyword of keywords) {
            if (keyword == expression) {
    return resultKeywords;

function detectIdentifierConstant(keywordList, newExpression) {
    newExpression.filter(keyword => !keywordList.includes(keyword))
                 .forEach(element => countIdentifierConstant++);

function detectKeywordIdentifier() {
    console.log(`The given expression:\n ${expression}\n`);
    let newExpression = hasSeparators(separators).split(" ")
                                                .filter(e => e != "");
    let keywordList = detectKeyword(keywords, newExpression);
    detectIdentifierConstant(keywordList, newExpression);

let countLexeme = countIdentifierConstant + countKeywords + countSeparators;
console.log(`The total lexeme: ${countLexeme}`);


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