Useless

Useless is a programming language that is Turing-complete and allows arbitrary input and output, but is nevertheless completely useless.

The following syntactic constructs are allowed:

• `, s, and k, which behave exactly as in Unlambda. These make the language Turing-complete
• Strings, contained between quotation marks. Escapes are allowed by placing a backslash before a character. Escaping a character always produces the character itself, i.e., \\ and \" work as expected and are the only escapes necessary or useful. Newlines are allowed in strings. This allows arbitrary output.
• An at sign (@), which pauses the execution of the program and waits for a line of arbitrary input.

1. I/O: All strings are printed, and all input is read, in the order in which they appear in the file. If the source file consists entirely of whitespace, the message Program is empty! is written to the standard output. Any unterminated strings are silently ignored. `, s, and k, outside of strings, are treated as whitespace.
2. Unlambda: Every `, s, and k outside of a string is gathered together, and is run as an Unlambda program. No output is printed. Any errors, including stack overflow and lack of memory, are silently ignored.
3. The program loops endlessly until it is terminated by the system (e.g., by pressing Ctrl-C or using your system's force quit feature).