BCT

# Interpreter for the turing-complete language "CT", as
# described at http://esolangs.org/wiki/Bitwise_Cyclic_Tag,
# in a single Python 3 expression.
#
# This effectively proves single-expression Python Turing-
# complete, without using eval/exec and assuming a limited
# call stack, which is the default.
#
# In this interpreter, 0 and 1 represent the equivalent CT
# instructions. 2 represents ";". Any other number appearing
# in the code will probably break things, so don't try.
#
# An additional challenge would be to write the program
# without __import__ and without the mutating list methods
# list.pop() and list.extend.

(lambda code, data_string:
    [data_string.pop(0) if command == 2 else
        data_string.extend([command] * data_string[0])
            for command in __import__("itertools").cycle(code)]
)(
    code=[2, 1, 0],
    data_string=[1, 1, 0]
)