Python Interpreter in Java

A lightweight Java-based interpreter that parses and executes a simple Python-like language. This project demonstrates how to build core interpreter components including lexical analysis, parsing, abstract syntax tree (AST) construction, and evaluation.

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🚀 Features

• Lexer: Tokenizes input source code into meaningful symbols.
• Parser: Constructs an Abstract Syntax Tree (AST) from tokens.
• AST: Represents the syntactic structure of the code.
• Interpreter: Evaluates the AST within an environment that maintains variable bindings.
• Environment: Stores and manages variable scopes and values.
• Input Support: Reads source code from input.txt for interpretation.

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📁 File Structure

• Lexer.java: Lexical analyzer for token generation.
• Parser.java: Parses tokens into an AST.
• AST.java: Defines node types of the AST.
• Interpreter.java: Core evaluator of AST nodes.
• Environment.java: Manages variable bindings.
• Token.java: Token definitions and types.
• Main.java: Entry point of the interpreter.
• input.txt: Input file containing the source code to interpret.

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🧠 Syntax Guide

🧮 Variable Declaration

let <identifier> = <expression>

Example:

let x = 5
let name = "John"

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➕ Arithmetic Operations

Supported Operators:

• + (Addition)
• - (Subtraction)
• * (Multiplication)
• / (Division)

Example:

let sum = 10 + 20
let product = x * 5
let result = (x + y) * 2

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🖨️ Print Statement

print(<expression>)

Example:

print(x)
print("Hello, World!")

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🧠 Expressions

Can include:

• Integers: 10, -5
• Strings: "hello"
• Identifiers: x, y
• Compound expressions: x + y * 2

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📂 Order of Operations

Standard precedence:

1. Parentheses ()
2. Multiplication / Division * /
3. Addition / Subtraction + -

Example:

let result = (2 + 3) * 4  # result = 20

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📝 Sample Program

let x = 10
let y = 20
let sum = x + y
print("Sum of x and y:")
print(sum)

Output:

Sum of x and y:
30

⚡ Performance Benchmark

Method	Time (Approx)
Python-Java interpreted (V1)	~371 ms ✅
Native Java loop	~50–150 ms
Python loop	~200–600 ms
Node.js (console.log)	~150–500 ms

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🛠️ Getting Started

Prerequisites

• Java Development Kit (JDK) 8 or higher

Compile and Run

javac *.java
java Main

Make sure to edit input.txt with your program before running.

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🗺️ Roadmap

• Conditionals: if, else, and comparison operators
• Loops: while, for, and control flow
• Functions: Definition and calls with parameters
• Boolean Logic: true, false, &&, ||, !
• Comments: Ignoring lines with //
• Arrays and Objects: Composite data structures

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🤝 Contributing

Pull requests and suggestions are welcome. Fork the repo and open an issue or PR.

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📜 License

This project is licensed under the MIT License.

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👤 Author

Advait Sankhe