INTERCAL is an esoteric programming language which was purposely designed to be confusing and not visually aesthetic. It has two maintained implementations in C-INTERCAL and CLC-INTERCAL. C-INTERCAL’s compiler is invoked by the ick command, and CLC-INTERCAL’s compiler is invoked by the sick command.

Some highlights of INTERCAL include

• Programmers must use PLEASE before statements to avoid compile errors due to insufficiently polite, but not too many PLEASE statements or the compiler will report errors due to being overly polite.
• Every call to a random number generator will introduce a random chance of the code failing to compile and report E774 RANDOM COMPILER BUG, and this chance to fail increases with the number of random number generator calls.
• If compiling in INTERCAL-72 mode, the compiler will report E111 COMMUNIST PLOT DETECTED if the programmer uses features that are newer than INTERCAL-72.

The full list of compiler errors and warnings for C-INTERCAL, as well as related documentation, can be found in the intercal/doc/ick.txi file under the “Errors and Warnings” chapter. If you want to quickly scroll through them, each of the entries are preceded by an @ieanchor tag.