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!aBF' is the language whose name is pronounced "not a brainfuck derivative". The language uses 5 commands which manipulate a sole accumulator. The accumulator initially starts at zero. Additionally, new commands can be appended to the end of the program during execution, making loops possible.


Command Name Description
! not Don't do the following command.
a AAAAAAAAAAAAAAA Output the accumulator LOUDLY (using the numbers you get with caps lock on)
B between Take everything between this B and the second-next B (or the end of the program), and replicate it to the end of the program a number of times equal to the value of the accumulator.
F five Add 5 to the accumulator.
' derivative Replace the value of the accumulator with its arithmetic derivative.


Output 420:




Replace the ? with F for 1 or ' for 0. As an example of this language's weirdness, the 1 case expands to a non-periodic pattern of a's and B's:


Truth-machine golfed:



  • Pyth implementation. Provide the !aBF' program as input. (Note: this implementation is improper, because numbers are not output in caps lock)