Creating a Compiler: Building a Simple Compiler / Interpreter (for my Own Programming Language) in Go

Compiler construction is a fascinating and challenging field of computer science. In this tutorial, I want to explore how to build a simple compiler or interpreter for “Lyron-thon” (my custom language — original, i know *don’t sue me, python devs*)… using the Go programming language. As such with my new “format” for my articles, I will cover the theory, practical code examples, applications, and limitations of this exciting endeavor.

Understanding the Basics

What is a Compiler?

A compiler is a software tool that translates high-level programming code into low-level machine code. It performs several essential tasks:

  1. Lexical Analysis (Scanning): Breaks the source code into tokens (words or symbols).
  2. Syntax Analysis (Parsing): Ensures that the source code follows a defined grammar and creates a parse tree or abstract syntax tree (AST).
  3. Semantic Analysis: Checks for semantic correctness and enforces language rules.
  4. Intermediate Code Generation: Converts the AST into an intermediate representation.
  5. Optimization: Enhances the intermediate code for performance.
  6. Code Generation: Translates the optimized intermediate code into target machine code.

What is an Interpreter?

An interpreter, on the other hand, reads and executes the source code line-by-line without generating an intermediate representation or machine code. It interprets and executes code in a more direct fashion.

Practical Implementation in Go

Let’s start building a simple interpreter for a custom language in Go. Our language will have variables, arithmetic operations, and print statements. We’ll walk through each step.

Step 1: Lexical Analysis (Scanning)

We begin by writing a scanner that tokenizes the source code. Go’s text/scanner package can help with this.

package main

import (
"fmt"
"text/scanner"
)
func main() {
var s scanner.Scanner
src := []byte("let x = 5 + 3; print(x);")
s.Init(scanner.Bytes, src)
for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
fmt.Printf("Token: %s, Value: %s\n", s.TokenText(), scanner.TokenString(tok))
}
}

Step 2: Syntax Analysis (Parsing)

Next, we create a parser to check if the source code follows our custom language’s grammar and build an abstract syntax tree (AST).

type Node interface{}

type Program struct {
Statements []Statement
}
type Statement interface{}
type LetStatement struct {
Identifier string
Value Expression
}
type Expression interface{}
type InfixExpression struct {
Left Expression
Operator string
Right Expression
}

Step 3: Semantic Analysis and Execution

We add semantic checks and execute the code based on the AST.

func evaluate(node Node) int {
switch node := node.(type) {
case *Program:
return evaluateStatements(node.Statements)
case *LetStatement:
// Implement variable assignment
case *InfixExpression:
// Implement arithmetic operations
}
return 0
}

Step 4: Printing Results

Finally, we add a simple print statement.

type PrintStatement struct {
Expression Expression
}

func printValue(value int) {
fmt.Println(value)
}
func main() {
// Parse the source code into an AST
// Evaluate and execute the AST
// Implement variable storage and retrieval
// Handle print statements
}

Applications

Building a compiler or interpreter can have several practical applications:

  1. Domain-Specific Languages (DSLs): Create custom languages tailored to specific problem domains, making it easier for domain experts to write code.
  2. Scripting Languages: Implement scripting languages for embedding in larger applications, allowing users to extend functionality.
  3. Educational Tools: Develop educational tools for teaching programming concepts and compiler theory.
  4. Code Optimization: Build custom compilers to optimize code for specific hardware or platforms.

Limitations

Building a full-fledged compiler is a complex task, and our simple example has limitations:

  1. Limited Language Features: Our custom language lacks advanced features like conditionals, loops, and functions.
  2. Performance: The interpreter is basic and not optimized for performance.
  3. Error Handling: Error handling and reporting are minimal.
  4. Security: Our interpreter doesn’t handle potential security issues like code injection.

Building a complete compiler or interpreter is a substantial undertaking. Still, it’s an educational journey that deepens your understanding of programming languages, compilers, and interpreters.

This is a really high-level overview of building a simple compiler or interpreter using Go. To create a fully functional language, you’d need to expand on these concepts and handle more language features, error cases, and optimizations. However, this could be considered an excellent starting point for someone considering designing their own language.

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