How Compilers Work: A step by step guide

When you write code, have you ever wondered what happens behind the scenes? How does the compiler transform your code into machine-readable instructions? In this post, we'll take a simplified journey through the compilation process, exploring the key steps involved in turning your code into an executable program.

Step 1: Lexical Analysis

The first step in the compilation process is lexical analysis. When you save your code in a .go file, the compiler's lexical analyzer breaks the code into individual tokens. These tokens are the building blocks of the programming language, including keywords (e.g., const), identifiers (e.g., a), literals (e.g., 9), and symbols (e.g., =).

Step 2: Syntax Analysis

The compiler's parser takes the tokens and checks if they form a valid program according to the language's syntax rules. This is where the compiler ensures that your code is structured correctly, with proper nesting, brackets, and semicolons.

Step 3: Semantic Analysis

After parsing, the compiler performs semantic analysis, which involves checking the meaning of the code. This is where the compiler checks the types of variables, ensures that operations are valid, and performs other semantic checks.

Step 4: Type Checking

In a statically typed language like Go, the compiler performs type checking during semantic analysis. This is where the compiler ensures that the types of variables and expressions are correct and compatible.

A Practical Example

Let's apply this to a simple example: const a int = 9

• Lexical analysis breaks this into tokens: const, a, int, =, 9
• Syntax analysis ensures that the tokens form a valid declaration
• Semantic analysis checks that a is being declared as a constant of type int and that 9 is a valid value for an int
• Type checking ensures that the type of 9 (an integer literal) is compatible with the declared type of a (an int)

If we change the code to: const a int = "nine"

• Lexical analysis breaks this into tokens: const, a, int, =, "nine"
• Syntax analysis ensures that the tokens form a valid declaration
• Semantic analysis checks that a is being declared as a constant of type int and that "nine" is being assigned to it
• Type checking fails because the type of "nine" (a string literal) is not compatible with the declared type of a (an int)

The compiler complains because it has detected a type mismatch during type checking, even before you run the code! This is the power of static type checking in languages like Go.

In conclusion, the compilation process involves a series of steps that transform your code into machine-readable instructions. By understanding these steps, you can appreciate the complexity and beauty of compiler design. Whether you're a seasoned developer or just starting out, knowing how compilers work can help you write better code and appreciate the tools that make programming possible.