It’s a turing tarpit, but one not very complicated at that (for something more esoteric see Malbolge or Whitespace).

The language is very simple, it has eight instructions. So I had to write a compiler for it. It turns out to be quite easy to do:

import static java.lang.System.out;

public class BrainFk
{
    public static void main(String[] args) {
        out.println("public class " + args[0] + "{");
        out.println("public static void main(String args[]) throws Throwable {");
        out.println("int[] memory = new int[30000];");
        out.println("int data = 0;");
        final String code = args[1];
        for(int i = 0; i < code.length(); i++) {
            char c = code.charAt(i);
            switch(c) {
                case '>':
                    out.println("++data;");
                    break;
                case '<':
                    out.println("--data;");
                    break;
                case '+':
                    out.println("++memory[data];");
                    break;
                case '-':
                    out.println("--memory[data];");
                    break;
                case '.':
                    out.println("System.out.print((char)(0xFF & memory[data]));");
                    break;
                case ',':
                    out.println("memory[data] = System.in.read();");
                    break;
                case '[':
                    out.println("while(memory[data] != 0) {");
                    break;
                case ']':
                    out.println("}");
                    break;
            }
        }
        out.println("}}");
    }
}

You can use it to compile the hello world sample from the Wikipedia page:

~>java BrainFk Hello "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>." > Hello.java
~>javac Hello.java
~>java Hello
Hello World!

Sometime I’ll have to post the Forth interpreter in Java I wrote (I know some might consider sacrilege to use both languages in the same sentence, but you can’t please everyone!).