Function key + Page Up/Down

Function key + Page Up/Down is an esoteric programming language by user:raiseafloppafan7741 in 2026. It is based on register machines.

Overview

There are infinite signed unbounded counters that are all initialized to zero. However, only one counter can be manipulated at a time.

State [N] defines a label. Despite the name, this has fall-through behavior and so is more like a label in assembly than a state in a state machine.

Page Up increments the current counter.

Page Down -> [State Number] decrements the current counter if it is not zero already. If it is zero, then it jumps to the specified label.

Control + Page Up moves to the previous counter. There are infinite counters in both directions, so doing this at the first counter is not undefined behavior.

Control + Page Down moves to the next counter.

Function key + Page Down resets the current counter to zero.

Control + C inputs a byte into the counter. EOF is -1.

Control + V outputs the counter as a byte modulo 256.

E freaking crashes the program in an elegant way.

Computational class

Function Key + Page Up/Down is a register machine with infinite unbounded registers and has the required subset of incrementing any register and decrementing any register or jumping if it is zero. Since Minsky machines only need 2 registers to be Turing-complete AND the subset of instructions {INC, JZDEC} are supported through the Page Up and Page Down -> [N] instructions, then Function Key + Page Up/Down is Turing-complete as well.

Examples

Invoke undefined behavior

Use alcohol instead of water when cleaning electronics, since apparently it dries faster and hopefully won't cause much damage.

Any less and you've got one less functioning keyboard.

E

One Time Cat

State 1
Control + C
Control + V

Cat program

State 1
  Control + C
  Page Up
  Page Down -> 2
  Control + V
  Function key + Page Down
  Page Down -> 1
State 2

A+B Problem

1-byte inputs and outputs the sum modulo 256.

State 1
  Control + C
  Control + Page Down
  Control + C
  Control + Page Down
State 2
  Control + Page Up
  Page Down -> 3
  Control + Page Up
  Page Up
  Control + Page Down
  Control + Page Down
  Page Down -> 2
State 3
  Control + Page Up
  Control + V

See also

• Minsky machine
• IF UPPERCASE KEYWORDS == ESOTERIC THEN DIE ELSE DIE END - Another programming language proved TC by Minsky machines, although by accident.
• MY E KEY BROKE