9 files changed, 176 insertions, 0 deletions
diff --git a/AbstractInterpreter.java b/AbstractInterpreter.java
new file mode 100644
index 0000000..7e7b82d
--- /dev/null
+++ b/AbstractInterpreter.java
@@ -0,0 +1,17 @@
+abstract class AbstractInterpreter implements Interpreter  {
+    public String print(String code) {
+	return code;
+    }
+
+    public String trace(String code, String param) {
+	return code;
+    }
+
+    public int minLength() {
+	return 0;
+    }
+
+    public int maxLength() {
+	return 1024 * 1024;
+    }
+}
diff --git a/BitString.java b/BitString.java
new file mode 100644
index 0000000..3060178
--- /dev/null
+++ b/BitString.java
@@ -0,0 +1,19 @@
+import java.lang.StringBuilder;
+
+class BitString extends java.util.BitSet {
+    public BitString(String s) {
+	for (int i=0; i<s.length(); i++)
+	    set(i, s.charAt(i) == '1');
+    }
+
+    public String toString() {
+	return toString(length());
+    }
+
+    public String toString(int size) {
+	java.lang.StringBuilder res = new java.lang.StringBuilder();
+	for (int i=0; i<size; i++)
+	    res.append(get(i)? "1" : "0");
+	return res.toString();
+    }
+}
diff --git a/ExternalInterpreter.java b/ExternalInterpreter.java
new file mode 100644
index 0000000..04776a8
--- /dev/null
+++ b/ExternalInterpreter.java
@@ -0,0 +1,33 @@
+// because writing java violates human rights
+
+import java.lang.Runtime;
+
+class ExternalInterpreter extends AbstractInterpreter {
+    ExternalInterpreter(String cmdName) {
+	this.cmdName = cmdName;
+    }
+
+    public String eval(String code, String param) {
+	java.lang.StringBuilder res = new java.lang.StringBuilder();
+	try {
+	    // exec program capturing its standart output
+	    String[] cmd = {"timeout", "-s", "9", "1", cmdName, code, param};
+	    Process p = java.lang.Runtime.getRuntime().exec(cmd);
+	    java.io.InputStream s = p.getInputStream();
+	    int c;
+	    // read stdout
+	    while (((c = s.read()) >= 0) && (res.length() < code.length())) {
+		switch (c) {
+		case '1': res.append("1"); break;
+		default:  res.append("0");
+		}
+	    }
+	    // pad string
+	    while (res.length() < code.length())
+		res.append("0");
+	} catch (java.io.IOException e) {}
+	return res.toString();
+    }    
+
+    String cmdName;
+}
diff --git a/Interpreter.java b/Interpreter.java
new file mode 100644
index 0000000..6dbff12
--- /dev/null
+++ b/Interpreter.java
@@ -0,0 +1,20 @@
+interface Interpreter {
+    /**
+     * return result of intepreted code, given param as argument
+     */
+    public String eval(String code, String param);
+
+    /**
+     * print the program code parses to
+     */
+    public String print(String code);
+
+    /**
+     * print a  trace of the intepretation of code given param
+     */
+    public String trace(String code, String param);
+
+    public int minLength();
+
+    public int maxLength();
+}
diff --git a/InterpreterStandalone.java b/InterpreterStandalone.java
new file mode 100644
index 0000000..8b33bde
--- /dev/null
+++ b/InterpreterStandalone.java
@@ -0,0 +1,14 @@
+/**
+ * use an Interpreter interface to create a standalone application
+ *
+ * Copy this file and change XorInterpreter to the name of your
+ * intepereter.
+ */
+class InterpreterStandalone {
+    public static void main(String[] args){
+	// use your interpreter here
+	Interpreter vm = new XorInterpreter(); 
+	String res = vm.eval(args[0], args[1]);
+	System.out.println(res);
+    }
+}
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..a0d18d2
--- /dev/null
+++ b/README.md
@@ -0,0 +1,24 @@
+Self-referential code testbed
+=============================
+
+This repository contains tools and examples to work with
+self-referential code.
+
+Concepts
+--------
+
+- Code: a bitstring of length n, containing of the ASCII chars zero or one
+- Interpreter: a program to interpret code as a program, run it given
+    code as input argument and return code as a result
+- Arena: a program to orchestrate one or more interpreters to act one code
+
+Content
+-------
+
+- TournementArena.java: an example arena
+- Interpreter.java: java interface each Interpreter has to follow
+- AbstractInterpreter.java: class to derive an interpreter; only eval is missing
+- InterpreterStandalone.java: convert a java interpreter class into a standalone program
+- XorInterpreter.java: an example interpreter
+- ExternalInterpreter.java: a class to call an external interpreter
+- BitString.java: helper to concert code into a BitSet for easier parsing
diff --git a/SElf REferential Code ARena b/SElf REferential Code ARena
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/SElf REferential Code ARena
diff --git a/TournementArena.java b/TournementArena.java
new file mode 100644
index 0000000..5a61c42
--- /dev/null
+++ b/TournementArena.java
@@ -0,0 +1,40 @@
+class TournementArena {
+    TournementArena(Interpreter[] vms, String[] arena) {
+	codeLen = arena[0].length();
+	this.vms     = vms;
+	this.arena   = arena;
+	rng = new java.util.Random();
+    }
+
+    String[] iterate() {
+	Interpreter vm = vms[rng.nextInt(vms.length)];
+	String
+	    code  = arena[rng.nextInt(arena.length)],
+	    param = arena[rng.nextInt(arena.length)],
+	    res = vm.eval(code, param);
+	arena[rng.nextInt(arena.length)] = res;
+	String [] ret = {code, param, res};
+	return ret;
+    }
+    
+    public static void main(String[] args){
+	// init arena
+	Interpreter[] vms = {
+	    new XorInterpreter(),
+	    new ExternalInterpreter("/bin/echo")
+	};
+	String[] arena = {"00", "01", "10", "11"}; // TODO: add random bit-strings
+	TournementArena a = new	TournementArena(vms, arena);
+
+	// run arena forever
+	while (true) {
+	    String[] r = a.iterate();
+	    System.out.println(r[0] + " ( " + r[1] + " ) -> " + r[2]);
+	}
+    }
+
+    int codeLen;
+    Interpreter[] vms;
+    String[] arena;
+    java.util.Random rng;
+}
diff --git a/XorInterpreter.java b/XorInterpreter.java
new file mode 100644
index 0000000..1b0ee0f
--- /dev/null
+++ b/XorInterpreter.java
@@ -0,0 +1,9 @@
+class XorInterpreter extends AbstractInterpreter {
+    public String eval(String code, String param) {
+	BitString
+	    x1 = new BitString(code),
+	    x2 = new BitString(param);
+	x1.xor(x2);
+	return x1.toString(code.length());
+    }    
+}