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Thread: BrainF*** interpreter

  1. #1
    Super Moderator helloworld922's Avatar
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    Default 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;
    		}
    	}
    }


  2. #2
    mmm.. coffee JavaPF's Avatar
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    Thumbs up Re: BrainF*** interpreter

    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.
    Please use [highlight=Java] code [/highlight] tags when posting your code.
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