INTERCAL is a programming language parody, the canonical esoteric programming language. It satirizes aspects of the FORTRAN and COBOL programming languages, as well as the proliferation of proposed language constructs and notations in the 1960s. Consequently, the humour may appear rather dated to modern readers brought up with C or Java.

INTERCAL was created by Don Woods and James Lyons , two Princeton University students, in 1972. The current version, C-INTERCAL, is maintained by Eric S. Raymond. INTERCAL is said by the original authors to stand for "Compiler Language With No Pronounceable Acronym".

INTERCAL is purposely different from all other computer languages in all ways but one; it is purely a written language. An excerpt from the INTERCAL Reference Manual will make the style of the language clear:

It is a well-known and oft-demonstrated fact that a person whose work is incomprehensible is held in high esteem. For example, if one were to state that the simplest way to store a value of 65536 in a 32-bit INTERCAL variable is:

DO :1 <- #0$#256

any sensible programmer would say that that was absurd. Since this is indeed the simplest method, the programmer would be made to look foolish in front of his boss, who would of course have happened to turn up, as bosses are wont to do. The effect would be no less devastating for the programmer having been correct.

The INTERCAL manual also contains such gems as:

Caution! Under no circumstances confuse the mesh with the interleave operator, except under confusing circumstances!

INTERCAL has many other features designed to make it even more aesthetically unpleasing to the programmer: it uses statements such as "COME FROM", "FORGET", and "PLEASE" and calls single and double quotes "sparks" and "rabbit ears" respectively. The equivalent of a "half mesh" or equals sign in most programming languages is a "<-", referred to as "gets" and made up of an "angle" and a "worm".

The Woods-Lyons implementation was actually used by several people at Princeton. The C-INTERCAL reimplementation, being available on the Internet, has made the language more popular with devotees of esoteric programming languages; there is even an alt.lang.intercal Usenet newsgroup devoted to the study and appreciation of INTERCAL and other esoteric languages.

The traditional "Hello, world!" program, written in C as:

        #include <stdio.h>
        int main(void) {
          printf("hello, world\n");
          return 0;
        }

appears in INTERCAL as:

        DO ,1 <- #13
        PLEASE DO ,1 SUB #1 <- #234
        DO ,1 SUB #2 <- #112
        DO ,1 SUB #3 <- #112
        DO ,1 SUB #4 <- #0
        DO ,1 SUB #5 <- #64
        DO ,1 SUB #6 <- #194
        DO ,1 SUB #7 <- #48
        PLEASE DO ,1 SUB #8 <- #22
        DO ,1 SUB #9 <- #248
        DO ,1 SUB #10 <- #168
        DO ,1 SUB #11 <- #24
        DO ,1 SUB #12 <- #16
        DO ,1 SUB #13 <- #214
        PLEASE READ OUT ,1
        PLEASE GIVE UP

Despite the language's being (intentionally) obtuse and wordy, INTERCAL is nevertheless Turing-complete: given enough memory, INTERCAL can solve any problem that a universal Turing machine can solve. Note that this says nothing about the time required to do so — a Sieve of Eratosthenes benchmark, computing all prime numbers less than 65536, was tested on a Sun SPARCStation-1. In C, it took less than 0.5 seconds; the same program in INTERCAL took over seventeen hours. (Stross, 1992)

It should be noted that almost any language allows notational horrors as great as or greater than INTERCAL's, as witnessed by the International Obfuscated C Code Contest.

According to the INTERCAL manual, "the aim in designing INTERCAL was to have no precedents", supposedly neither in flow control features, nor in data manipulation operators. Unfortunately, they missed: a machine instruction in a Soviet mainframe computer BESM-6, released in 1967 is effectively equivalent to INTERCAL's "select" operator.

External links

• INTERCAL home page on the Web.
• INTERCAL Resources on the Web, including several implementations
• INTERCAL — the Language from Hell (Charles Stross, Computer Shopper [UK], September 1992)
• INTERCAL reference manual

Part of an earlier version of this article contains text from The Jargon File 4.2.3 Mar 2001.