[gleenn]

Brainfuck, while difficult to actually use, is very easy to implement. There is one array data structure of ints, and iirc 8 operators that work on the array. They either manipulate the current pointer to the array cell by either moving up or down, or increment or decrement the value there. And then there is a simple conditional and a print command. That's it. You can write that in an afternoon if not in an interview session. Now actually doing something productive with the language is a whole different situation. It's clearly Turing-complete as the infinite paper is just the array and the operations are exact copies. A fun little exercise.