HQ9+ is a joke language with four instructions:
- H: Print "hello, world"
- Q: Print the program's source code
- 9: Print the lyrics to "99 Bottles of Beer"
- +: Increment the accumulator
Although the language is not of serious interest by itself, it can be useful to implement HQ9+ in a new esoteric programming language, since doing so proves that all the tasks above, except the quine, are possible. HQ9+ was created in 2001 by Cliff L. Biffle.
- HQ9++, an object-oriented extension of HQ9+.
- CHIQRSX9+, another HQ9+ extension supposedly Turing complete.
- HQ9+B, an ℒ-complete extension of HQ9+.
- HQ9+2D, a 2-D extension of HQ9+.
- H9+, with one fewer instruction but still capable of all of the tasks.
- FISHQ9+, HQ9+ and deadfish combined.
- HI9+, which replaces Q with an instruction that prints the interpreter's source code.
- +, where there is only +, and other characters are ignored.
- Hq9eFuck, HQ9+, brainfuck and Deep Thought combined.
- HQ9+ home page (from the Wayback Machine; retrieved on 2 June 2009)
- HQ9+ as an embedded language in Haskell
- Online HQ9+ interpreter realized with PHP
- HQ9+ interpreter in C by User:mmphosis
- HQ9+ interpreter in Pascal by User:GrandKeyboard
- hq9plus - HQ9P implementation for Parrot