INTERCAL resurfaces: its 1972 compiler rejected code without “PLEASE”

INTERCAL’s original 1972 compiler source code turned up again and was published online in June 2025, which put the spotlight back on one of programming’s strangest inside jokes. That includes its famous “PLEASE” rule: the compiler could throw out code for being too rude, or for laying the politeness on too thick.

Princeton students Don Woods and James M. Lyon created INTERCAL as a satire of the languages people were using at the time. The name was short for “Compiler Language With No Pronounceable Acronym.” And yes, it really could reject your code for being either insufficiently polite or excessively polite. That quirk was baked into the original compiler, even if the first documentation didn’t spell it out.

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The whole thing was built to be difficult on purpose. Its syntax fought your instincts. It had commands like IGNORE, FORGET, and COME FROM, took numeric input written out as English words, and produced output in modified Roman numerals.

If you’re into computing history or esoteric programming, this rediscovery is worth your time. INTERCAL was still Turing-complete, and it helped carve out the idea that a programming language could be satire, art, comedy, and critique, not just a technical tool.

You can read the newly published INTERCAL source code online in the June 2025 release.