What is Lexical analysis

Lexical Analysis in Artificial Intelligence

Artificial intelligence is one of the most popular fields of computer science, which focuses on the development of intelligent machines that can perform tasks that traditionally require human intelligence. Among various techniques to create such intelligent machines, lexical analysis (also known as lexical scanning or tokenization) is a fundamental process that helps machines understand human languages.

Lexical analysis is the first step in the compilation process of computer programs. It takes the source code written in a programming language and scans it for valid tokens or identifiers. The tokens or identifiers are then passed to the next phase of the compilation process for processing. In this article, we will look in-depth at lexical analysis and how it works in artificial intelligence applications.

What is Lexical Analysis?

Lexical analysis is the process of breaking a stream of characters or symbols into meaningful words, phrases or tokens. In simple terms, the computer reads the input text character by character and converts it into a sequence of tokens, which are expressions with an assigned meaning. For instance, consider the sentence "The quick brown fox jumps over the lazy dog." This sentence may contain several tokens, such as "The," "quick," "brown," "fox," "jumps," "over," "the," "lazy," and "dog," each with an assigned meaning.

During the lexical analysis process, the computer program analyzes the input text to identify special characters, such as operators, punctuations, and white spaces. It then forms a sequence of individual tokens from the set of characters based on a set of predetermined rules, called the lexical grammar of the language. If the input character sequence does not match any of the lexical grammar rules, the analysis results in an error. Otherwise, the output sequence of tokens is passed on for further processing.

How does Lexical Analysis work?

Lexical analysis works by processing each character in the input text from left to right and combining them into meaningful tokens. This process involves several steps, including character scanning, tokenization, and categorization.

1. Character Scanning

The first step in lexical analysis is to scan each character in the input text from left to right. The scanner reads the input text character by character and identifies the start and end of each token.

2. Tokenization of the Characters

The second step is tokenization of the characters. Tokenization is the process of forming meaningful tokens from a sequence of characters. During this step, the scanner identifies and separates groups of characters that represent a single token or identifier based on lexical rules.

3. Categorization of Tokens

The final step in lexical analysis is the categorization of tokens. During this step, the program determines the type of each token. Tokens may be separated into various categories, such as keywords, symbols, identifiers, literals, and comments. Each category has a specific purpose in the programming language and plays a role in understanding the input text.

Why is Lexical Analysis essential in artificial intelligence applications?

Lexical analysis plays a critical role in artificial intelligence applications that involve natural language processing (NLP). NLP is a field of study that focuses on enabling machines to process, understand and generate human language. It's crucial for tasks such as translation, sentiment analysis, chatbots, and virtual assistants.

NLP involves dealing with unstructured data, which includes natural language text, audio, and video. Thus, lexical analysis helps to structure the data by breaking down the text into smaller, meaningful units and categorizing them into specific groups. This allows machine learning algorithms to analyze the data effectively and draw insights from it.

Examples of Lexical Analysis in Artificial Intelligence
Sentiment Analysis

Sentiment analysis is a popular application of NLP that involves determining the emotional tone in a piece of text. The process involves analyzing the text by breaking it down into meaningful tokens and categorizing the tokens based on their positivity, negativity or neutrality. Lexical analysis helps to identify the positive, negative, or neutral words in the text and categorize them accordingly.


Chatbots are virtual assistants that are designed to interact with humans through conversations. The process involves breaking down a user's message into a sequence of tokens, which are then processed to understand the user's intention. Examples of tokens in chatbots include greetings, questions, commands, and responses. Lexical analysis helps in the identification and categorization of these tokens, making it easier for the chatbot to understand and respond to the user's requests.

Language translation

Language translation involves converting text from one language to another. During this process, the input text is broken down into tokens, which are then analyzed and translated. Lexical analysis helps to identify and categorize the tokens in the input text, making it easier for machine learning algorithms to translate the text accurately.


Lexical analysis is a critical process that plays a critical role in artificial intelligence applications such as natural language processing. The process involves breaking down a piece of text into meaningful tokens, which are then categorized based on their type. The categorized tokens make it easier for machine learning algorithms to analyze and derive insights from the input data.