HQ9+ is a simple but elegant programming language that is very efficient for coding certain classes of computer programs. It has four commands, each represented by a single character: H, Q, 9, and + (hence the name).
- The H command prints out "Hello, world
- The Q command prints out a copy of the source code of the program (i.e., it's a quine).
- The 9 command prints out the lyrics for 99 Bottles of Beer on the Wall.
- The + command increments the accumulator.
This program would output "Hello, world! Hello, world! HHQ+HQ++ Hello, world! HHQ+HQ++" as well as incrementing the accumulator three times.
It is vacuously true that all useful programs written in HQ9+ run over twice as fast as the same programs written in any other language.
Of course, HQ9+ is a joke; each command represents a common task that beginners are given when learning a new programming language. A common exercise, for example, is to write a computer program that prints "Hello, world. There are some programming languages in which this is actually quite difficult; however, in HQ9+ the task is elementary, since the program "H" will accomplish the task. One of the hardest tasks in many programming languages is to print a quine, or print its own source code. However, in HQ9+, this is also trivial.
HQ9+ interpreters are extremely simple to write, so there have been many written. For example, HQ9+ interpreter was written (in python) in around five minutes yet it is only 18 lines long. And, HQ9+ compiler (in C, compiles HQ9+ programs to C code) is only about 40 lines long.