What lexical analysis is
Lexical analysis is the process of converting a sequence of characters, such as the text of source code, into a sequence of tokens. It is typically the first stage of a compiler or interpreter. A token is a meaningful unit, like a keyword, a name, a number, or a symbol. By grouping raw characters into these units, lexical analysis gives the following stages something structured to work with.
From characters to tokens
Source code starts as just a stream of characters with no inherent grouping. Lexical analysis scans this stream and identifies the meaningful pieces, producing tokens. For example, a sequence of letters might become a single identifier token, and a run of digits a number token. This grouping turns a flat sequence of characters into a sequence of labeled units that carry meaning.
The role of the lexer
The component that performs lexical analysis is often called a lexer, scanner, or tokenizer. Its job is to read the input and emit tokens, discarding things that do not matter for later stages, such as whitespace in many languages. The lexer effectively prepares the input, so the parts that follow can focus on structure and meaning rather than individual characters.
Why it comes first
Lexical analysis comes first because it simplifies the work of later stages. Parsing, which determines the grammatical structure of the code, is much easier when it operates on tokens rather than raw characters. By handling the lowest-level grouping up front, lexical analysis lets the rest of the compiler reason at a higher level, which keeps the overall design cleaner and more manageable.
Lexical analysis in the pipeline
Lexical analysis is one step in the pipeline that turns source code into something a computer can run. After tokens are produced, they are passed on to be parsed and further processed. Understanding lexical analysis clarifies how the journey from human-readable code to execution begins: by breaking the text into the basic building blocks of the language.
Why it matters
Lexical analysis is a foundational step in how programming languages are processed. Understanding what it is - turning source characters into meaningful tokens - clarifies the first stage of compilers and interpreters. For anyone interested in how code is understood by computers, it is a valuable concept to understand.
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See also: What is a compiler vs interpreter?, What is parsing? Explained.
Sources
Published date reflects the original event date (2026-06-23). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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