What is lexical analyzer in compiler design?
A lexical analyzer, also called a scanner, is the first phase of a compiler. Its job is to read the raw source code (a sequence of characters) and convert it into a sequence of tokens. Tokens are the meaningful building blocks of a programming language, such as keywords, identifiers, operators, literals, and punctuation. For example, the code int x = 10; would be broken into tokens like [int] [x] [=] [10] [;].
The lexical analyzer is the first part of a compiler's job. It looks at your code, the text you wrote. Its main job is to chop the code into small, sensible bits. We call these 'tokens'.
A token is something like a keyword (e.g., if or while), a variable name, or a symbol like +. It also cleans the code up. It gets rid of comments and empty spaces because the next part doesn't need them.
After it's done, it passes this neat stream of tokens to the next stage, which is the parser.
Think of a lexical analyzer as a translator between human-readable code and machine-parsable units. Without it, the compiler would have to directly interpret every character in the source file, which would be inefficient and error-prone. Lexical analysis streamlines the entire compilation process.
In practical compiler design, tools like Lex or Flex are used to generate lexical analyzers automatically. A programmer just defines patterns using regular expressions, and the tool generates the C code for the scanner. This demonstrates how theoretical concepts in compiler design are directly used in real-world software development.
The lexical analyzer performs several key tasks:- Removing whitespace and comments: which are not needed for syntax analysis.- Grouping characters into tokens: ensuring valid identifiers, numbers, etc.- Error detection: flagging invalid characters. This makes the next compiler phase, the syntax analyzer (parser), much easier to handle.