Brainf**

BF.java

import java.io.IOException;
import java.util.LinkedList;

public class BF {
	private interface Visitor {
		void visit (Loop loop);
		void visit (Left left);
		void visit (Right right);
		void visit (Increment increment);
		void visit (Decrement decrement);
		void visit (Input input);
		void visit (Output output);
		void visit (Program program);
	}
	private interface Node {
		void accept (Visitor v);
	}
	private class Left implements Node {
		public void accept (Visitor v) {
			v.visit(this);
		}
	}
	private class Right implements Node {
		public void accept (Visitor v) {
			v.visit(this);
		}
	}
	private class Increment implements Node {
		public void accept (Visitor v) {
			v.visit(this);
		}
	}
	private class Decrement implements Node {
		public void accept (Visitor v) {
			v.visit(this);
		}
	}
	private class Input implements Node {
		public void accept (Visitor v) {
			v.visit(this);
		}
	}
	private class Output implements Node {
		public void accept (Visitor v) {
			v.visit(this);
		}
	}
	private class Sequence implements Node {
		private LinkedList<Node> children;
		public Sequence() {
			children = new LinkedList<Node>();
		}
		public void accept (Visitor v) {
			for (Node child : children) {
				child.accept(v);
			}
		}
		public void add (Node instruction) {
			children.add(instruction);
		}
	}
	private class Loop implements Node {
		public Node body;
		public Loop (Node body) {
			this.body = body;
		}
		public void accept (Visitor v) {
			v.visit (this);
		}
	}
	public static class Program implements Node {
		public Node body;
		public Program (Node body) {
			this.body = body;
		}
		public void accept(Visitor v) {
			v.visit (this);
		}
	}
	private int i = 0;
	private Sequence doParse (String str) {
		Sequence seq = new Sequence();
		char c;
		while (i < str.length ()) {
			c = str.charAt (i);
			i++;
			if (c == '<') seq.add (new Left ());
			if (c == '>') seq.add (new Right ());
			if (c == '+') seq.add (new Increment ());
			if (c == '-') seq.add (new Decrement ());
			if (c == '.') seq.add (new Output ());
			if (c == ',') seq.add (new Input ());
			if (c == '[') seq.add (new Loop (doParse (str)));
			if (c == ']') return seq;
		}
		return seq;
	}
	public static Program parse (String str) {
		return new Program (new BF().doParse(str));
	}
	public static void main(String[] args) {
		Node ascii = BF.parse("+[.+]");
		ascii.accept(new BF.InterpreterVisitor());
		Node hello = BF.parse("++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.");
		hello.accept(new BF.InterpreterVisitor());
		Node beer = BF.parse(">+++++++++[<+++++++++++>-]<[>[-]>[-]<<[>+>+<<-]>>[<<+>>-]>>>[-]<<<+++++++++<[>>>+<<[>+>[-]<<-]>[<+>-]>[<<++++++++++>>>+<-]<<-<-]+++++++++>[<->-]>>+>[<[-]<<+>>>-]>[-]+<<[>+>-<<-]<<<[>>+>+<<<-]>>>[<<<+>>>-]>[<+>-]<<-[>[-]<[-]]>>+<[>[-]<-]<++++++++[<++++++<++++++>>-]>>>[>+>+<<-]>>[<<+>>-]<[<<<<<.>>>>>-]<<<<<<.>>[-]>[-]++++[<++++++++>-]<.>++++[<++++++++>-]<++.>+++++[<+++++++++>-]<.><+++++..--------.-------.>>[>>+>+<<<-]>>>[<<<+>>>-]<[<<<<++++++++++++++.>>>>-]<<<<[-]>++++[<++++++++>-]<.>+++++++++[<+++++++++>-]<--.---------.>+++++++[<---------->-]<.>++++++[<+++++++++++>-]<.+++..+++++++++++++.>++++++++[<---------->-]<--.>+++++++++[<+++++++++>-]<--.-.>++++++++[<---------->-]<++.>++++++++[<++++++++++>-]<++++.------------.---.>+++++++[<---------->-]<+.>++++++++[<+++++++++++>-]<-.>++[<----------->-]<.+++++++++++..>+++++++++[<---------->-]<-----.---.>>>[>+>+<<-]>>[<<+>>-]<[<<<<<.>>>>>-]<<<<<<.>>>++++[<++++++>-]<--.>++++[<++++++++>-]<++.>+++++[<+++++++++>-]<.><+++++..--------.-------.>>[>>+>+<<<-]>>>[<<<+>>>-]<[<<<<++++++++++++++.>>>>-]<<<<[-]>++++[<++++++++>-]<.>+++++++++[<+++++++++>-]<--.---------.>+++++++[<---------->-]<.>++++++[<+++++++++++>-]<.+++..+++++++++++++.>++++++++++[<---------->-]<-.---.>+++++++[<++++++++++>-]<++++.+++++++++++++.++++++++++.------.>+++++++[<---------->-]<+.>++++++++[<++++++++++>-]<-.-.---------.>+++++++[<---------->-]<+.>+++++++[<++++++++++>-]<--.+++++++++++.++++++++.---------.>++++++++[<---------->-]<++.>+++++[<+++++++++++++>-]<.+++++++++++++.----------.>+++++++[<---------->-]<++.>++++++++[<++++++++++>-]<.>+++[<----->-]<.>+++[<++++++>-]<..>+++++++++[<--------->-]<--.>+++++++[<++++++++++>-]<+++.+++++++++++.>++++++++[<----------->-]<++++.>+++++[<+++++++++++++>-]<.>+++[<++++++>-]<-.---.++++++.-------.----------.>++++++++[<----------->-]<+.---.[-]<<<->[-]>[-]<<[>+>+<<-]>>[<<+>>-]>>>[-]<<<+++++++++<[>>>+<<[>+>[-]<<-]>[<+>-]>[<<++++++++++>>>+<-]<<-<-]+++++++++>[<->-]>>+>[<[-]<<+>>>-]>[-]+<<[>+>-<<-]<<<[>>+>+<<<-]>>>[<<<+>>>-]<>>[<+>-]<<-[>[-]<[-]]>>+<[>[-]<-]<++++++++[<++++++<++++++>>-]>>>[>+>+<<-]>>[<<+>>-]<[<<<<<.>>>>>-]<<<<<<.>>[-]>[-]++++[<++++++++>-]<.>++++[<++++++++>-]<++.>+++++[<+++++++++>-]<.><+++++..--------.-------.>>[>>+>+<<<-]>>>[<<<+>>>-]<[<<<<++++++++++++++.>>>>-]<<<<[-]>++++[<++++++++>-]<.>+++++++++[<+++++++++>-]<--.---------.>+++++++[<---------->-]<.>++++++[<+++++++++++>-]<.+++..+++++++++++++.>++++++++[<---------->-]<--.>+++++++++[<+++++++++>-]<--.-.>++++++++[<---------->-]<++.>++++++++[<++++++++++>-]<++++.------------.---.>+++++++[<---------->-]<+.>++++++++[<+++++++++++>-]<-.>++[<----------->-]<.+++++++++++..>+++++++++[<---------->-]<-----.---.+++.---.[-]<<<]");
		beer.accept(new BF.InterpreterVisitor());
		Node fibonacci = BF.parse("+++++++++++>+>>>>++++++++++++++++++++++++++++++++++++++++++++>++++++++++++++++++++++++++++++++<<<<<<[>[>>>>>>+>+<<<<<<<-]>>>>>>>[<<<<<<<+>>>>>>>-]<[>++++++++++[-<-[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]>[<<[>>>+<<<-]>>[-]]<<]>>>[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]>[<<+>>[-]]<<<<<<<]>>>>>[++++++++++++++++++++++++++++++++++++++++++++++++.[-]]++++++++++<[->-<]>++++++++++++++++++++++++++++++++++++++++++++++++.[-]<<<<<<<<<<<<[>>>+>+<<<<-]>>>>[<<<<+>>>>-]<-[>>.>.<<<[-]]<<[>>+>+<<<-]>>>[<<<+>>>-]<<[<+>-]>[<+>-]<<<-]");
		fibonacci.accept(new BF.InterpreterVisitor());
		Node rot13 = BF.parse("+[,+[-[>+>+<<-]>[<+>-]+>>++++++++[<-------->-]<-[<[-]>>>+[<+<+>>-]<[>+<-]<[<++>>>+[<+<->>-]<[>+<-]]>[<]<]>>[-]<<<[[-]<[>>+>+<<<-]>>[<<+>>-]>>++++++++[<-------->-]<->>++++[<++++++++>-]<-<[>>>+<<[>+>[-]<<-]>[<+>-]>[<<<<<+>>>>++++[<++++++++>-]>-]<<-<-]>[<<<<[-]>>>>[<<<<->>>>-]]<<++++[<<++++++++>>-]<<-[>>+>+<<<-]>>[<<+>>-]+>>+++++[<----->-]<-[<[-]>>>+[<+<->>-]<[>+<-]<[<++>>>+[<+<+>>-]<[>+<-]]>[<]<]>>[-]<<<[[-]<<[>>+>+<<<-]>>[<<+>>-]+>------------[<[-]>>>+[<+<->>-]<[>+<-]<[<++>>>+[<+<+>>-]<[>+<-]]>[<]<]>>[-]<<<<<------------->>[[-]+++++[<<+++++>>-]<<+>>]<[>++++[<<++++++++>>-]<-]>]<[-]++++++++[<++++++++>-]<+>]<.[-]+>>+<]>[[-]<]<]");
		rot13.accept(new BF.InterpreterVisitor());
	}
	public static class PrintVisitor implements Visitor {
		public void visit (Left n) { System.out.print('<'); }
		public void visit (Right n) { System.out.print('>'); }
		public void visit (Increment n) { System.out.print('+'); }
		public void visit (Decrement n) { System.out.print('-'); }
		public void visit (Input n) { System.out.print(','); }
		public void visit (Output n) { System.out.print('.'); }
		public void visit (Loop n) { System.out.print('['); n.body.accept(this); System.out.print(']'); }
		public void visit (Program n) { n.body.accept(this); }
	}
	public static class InterpreterVisitor implements Visitor {
		private byte[] array;
		private int pointer;
		
		public void visit (Left n) { pointer--; }
		public void visit (Right n) { pointer++; }
		public void visit (Increment n) { array[pointer]++; }
		public void visit (Decrement n) { array[pointer]--; }
		public void visit (Input n) { try {
			array[pointer] = (byte) System.in.read();
		} catch (IOException e) {
		} }
		public void visit (Output n) { System.out.print((char)array[pointer]); }
		public void visit (Loop n) {
			while (array[pointer] != 0) {
				n.body.accept(this);
			}
		}
		public void visit (Program n) {
			array = new byte[30000];
			pointer = 0;
			n.body.accept(this);
		}
	}
}