--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/interps/qbf/qbf.py	Sun Dec 09 19:30:08 2012 +0000
@@ -0,0 +1,90 @@
+#!/usr/bin/python
+
+# A Quantum Brainfuck interpreter
+# For now, very basic with no error checking
+# Implements extra commands:
+# '1' initializes the current cell to 1
+# '0' initializes the current cell to 0
+# '#' outputs the probabilities of all the different possible states
+
+import qubit
+import sys
+
+DEBUG = True  # Adds some extra helpful commands
+
+if len(sys.argv) != 2:
+    print "Usage:", sys.argv[0], "<filename>"
+    raise SystemExit
+
+infile = file(sys.argv[1])
+
+program = infile.read()
+memory = qubit.Register(2)
+qubit_positions = range(2)
+mp = 0
+cp = 0
+
+while cp < len(program):
+    cmd = program[cp]
+    if cmd == '<':
+        mp -= 1
+    elif cmd == '>':
+        mp += 1
+        if mp >= memory.length:
+            qubit_positions.append(memory.length)
+            memory.add_bit()
+        if mp >= 20:
+            # just a precaution, feel free to remove this
+            print "Pointer moved right too many qubits; terminating"
+    elif cmd == '%':
+        qubit.Hadamard.apply(memory, [qubit_positions[mp]])
+    elif cmd == '!':
+        qubit.CV.apply(memory,[qubit_positions[mp],qubit_positions[mp+1]])
+    elif cmd == '&':
+        temp = qubit_positions[mp]
+        qubit_positions[mp] = qubit_positions[mp+1]
+        qubit_positions[mp+1] = temp
+    elif cmd == '.':
+        # Output the qubit
+        # For now, output it as a '1' or '0' and output causes observation
+        output = memory.observe(qubit_positions[mp])
+        print output,
+    elif cmd == ',':
+        # input a qubit
+        i = raw_input("\nPlease enter 1 or 0: ")
+        i = int(i)
+        assert i == 1 or i == 0
+        memory.set(qubit_positions[mp], i)
+    elif cmd == '[':
+        # observe the current qubit, loop if it's 1
+        bit = memory.observe(qubit_positions[mp])
+        if not bit:
+            # skip till the end of the loop
+            bracket_level = 1
+            while bracket_level:
+                cp += 1
+                if program[cp] == '[': bracket_level += 1
+                if program[cp] == ']': bracket_level -= 1
+    elif cmd == ']':
+        # just go back to the matching bracket
+        bracket_level = -1
+        while bracket_level:
+            cp -= 1
+            if program[cp] == '[': bracket_level += 1
+            if program[cp] == ']': bracket_level -= 1
+        cp -= 1
+    # Now, some helpful debugging commands:
+    elif DEBUG and cmd == '1':
+        memory.set(qubit_positions[mp], 1)
+    elif DEBUG and cmd == '0':
+        memory.set(qubit_positions[mp], 0)
+    elif DEBUG and cmd == '#':
+        # pretty print memory contents
+        for i in range(len(memory.contents)):
+            print '|'+''.join([str(b) for b in qubit.n2bits(i,memory.length)])+'>',
+            print '%.2f' % (abs(memory.contents[i])**2),
+
+    else:
+        # do nothing
+        pass
+    cp += 1