I've always admired the back cover of the APL79 conference proceedings. It's mostly a random jumble of APL symbols, but even a cursory glance reveals assorted error messages, system commands, and other phrases mixed in with the symbols. If you look a bit longer, you'll notice recognizable code, apparently the program that produced the cover. And indeed it is. The author of the program has included enough information to recreate the program, its arguments, the index origin and the phrase list; everything you need to reproduce the cover. But not without throwing in a few red herrings! Three phrases appear without being included in the phrase list, and there are some sneaky twists to some of the phrases.
For an enjoyable puzzle, try to reproduce the back cover for yourself. (Part 2 of the proceedings contains the full, unclipped listing.) Or you can look at my solution by clicking on the Solution button below.
Does anyone know who wrote this charming program and ran it back on April 24, 1979, at 12:48:12.351 AM?
P.S. It turns out the COVER function was written by Paul Penfield, the APL79 Program Chairman. He mentioned one additional challenge: Can you name the nine languages that appear in the listing?
APL SPOKEN HERE HER TALES APL AQUI SE HABLA APL HER SNAKKES APL ICI ON PARLE APL HÄR TALAS APL HIER SPRICHT MAN APL QUI SI PARLA APL APL HIC DICITURThe Back Cover