Thread: BrainF*** interpreter

Just for fun, I decided to write a BrainF*** interpreter in Java (sorry for the lack of comments, I was feeling pretty lazy)

By default, it will look for the file "test.b", but you can pass it a command-line argument and it will open that file instead.

For more info about BrainF***: Wikipedia: BrainF***

import java.io.*;
import java.util.ArrayList;
 
/**
 * @author helloworld922
 * 
 */
public class BrainF
{
	public static void main(String[] args)
	{
		try
		{
			BufferedReader reader;
			if (args.length == 0)
			{
				reader = new BufferedReader(new FileReader("test.b"));
			}
			else
			{
				reader = new BufferedReader(new FileReader(args[0]));
			}
			ArrayList<Object> commands = BrainF.parse(reader, false);
			BrainF.execute(commands, new Node(), false);
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
 
	public static Node execute(ArrayList<?> commands, Node currentNode, boolean inLoop)
			throws IOException
	{
		if (inLoop)
		{
			while (currentNode.val != 0)
			{
				currentNode = BrainF.execute(commands, currentNode, false);
			}
		}
		else
		{
			for (int i = 0; i < commands.size(); i++)
			{
				if (commands.get(i) instanceof ArrayList<?>)
				{
					currentNode = BrainF.execute((ArrayList<?>) commands.get(i), currentNode, true);
				}
				else if (commands.get(i).equals(">"))
				{
					if (currentNode.next == null)
					{
						currentNode.next = new Node();
						currentNode.next.prev = currentNode;
					}
					currentNode = currentNode.next;
				}
				else if (commands.get(i).equals("<"))
				{
					if (currentNode.prev == null)
					{
						currentNode.prev = new Node();
						currentNode.prev.next = currentNode;
					}
					currentNode = currentNode.prev;
				}
				else if (commands.get(i).equals("+"))
				{
					currentNode.val++;
					if (currentNode.val > 0xFF)
					{
						currentNode.val = 0;
					}
				}
				else if (commands.get(i).equals("-"))
				{
					currentNode.val--;
					if (currentNode.val < 0 || currentNode.val > 0xFF)
					{
						currentNode.val = 0xFF;
					}
				}
				else if (commands.get(i).equals("."))
				{
					System.out.print((char) currentNode.val);
				}
				else if (commands.get(i).equals(","))
				{
					currentNode.val = System.in.read();
				}
				else
				{
					System.err.print(commands.get(i));
				}
			}
		}
		return currentNode;
	}
 
	public static ArrayList<Object> parse(BufferedReader reader, boolean inLoop) throws IOException
	{
		ArrayList<Object> commands = new ArrayList<Object>();
		int read = 0;
		while (read != -1)
		{
			read = reader.read();
			if (read == '>' || read == '<' || read == '+' || read == '-' || read == '.' || read == ',')
			{
				commands.add("" + (char) read);
			}
			else if (read == '[')
			{
				commands.add(BrainF.parse(reader, true));
			}
			else if (read == ']')
			{
				if (inLoop)
				{
					return commands;
				}
				else
				{
					System.err.println("Error! Unmatching parenthesis!");
					throw new IOException();
				}
			}
		}
		if (inLoop)
		{
			System.err.println("No closing parenthesis found!");
			throw new IOException();
		}
		return commands;
	}
 
	private static class Node
	{
		public Node prev, next;
		public int val;
 
		public Node()
		{
			this.prev = null;
			this.next = null;
			this.val = 0;
		}
 
		@Override
		public String toString()
		{
			Node temp = this;
			String str = "";
			while (temp.prev != null)
			{
				temp = temp.prev;
			}
			do
			{
				str += temp.val + " ";
				temp = temp.next;
			}
			while (temp != null);
			return str;
		}
	}
}

Thats brilliant helloworld!! I'm going to give it a go now

We should start a new software forum where we can offer these types of programs.