INTERCAL

INTERCAL is a programming language which was created in 1972 as a parody. Its constructs are designed to be maximally obtuse and incomprehensible, with statements such as PLEASE GIVE UP (which terminates the program; the "PLEASE" part is optional on any statement, but failing to use it enough causes an impoliteness error), WRITE IN (which accepts input), and READ OUT (which generates output). Later versions added the infamous COME FROM statement, the inverse of the more common GO TO (which was "considered harmful" in a famous computer science paper).

In the original version, all numeric input was done with spelled-out numbers, while all numeric output was in Roman numerals. A later variant version used ternary (base 3).

The language is actually Turing-complete, and hence capable of implementing any algorithm, though the programmer might be driven into advanced stages of insanity from the attempt.

Some versions (e.g., the Intercal on Interstates web framework) apparently use source code files with a .i extension.