4-list is a simplification of I/D machine(actually being only 1-commanded, and it supports I/O).
It only works when the alphabet number is 4. If the word doesn't end in "!" : Increment the bit pointed. Else : Print the bit pointed as ASCII character. Jump to the byte numbered as the bit pointed.
As a loop, it is already in an infinite loop.
It is Turing-complete, since equivalence to I/D machine.