I lost my Emacs session today because I accidentally called the length function on an extremely long improper list.

But Guile prints the entire thing when it reports the error that happens when the length function gets to the improper part of the list. It tried to print a few million elements just to tell me which list wasn't a proper list.

To reproduce the error should be easy:

(length

(let loop ((result 'x)

(n 50000000))

(if (= n 0)

result

(loop (cons n result) (- n 1)))))

Emacs is more sensitive to the problem because it doesn't throw away any of the output. It's also really bad over SSH. The above test is enough to dump output to a local terminal for a minute or two, or to uninterruptibly tie up an SSH session for several minutes.