ANS Forth: 0 >in 2dup ! ! which leads to: $ gforth Gforth 0.7.0, Copyright (C) 1995-2008 Free Software Foundation, Inc. Gforth comes with ABSOLUTELY NO WARRANTY; for details type `license' Type `bye' to exit 0 >in 2dup ! ! :1: Stack overflow 0 >in 2dup >>>!<<< ! Backtrace: $B71DF6EC r> $B71D34A4 perform $B71DD654 (search-wordlist) $3 $0 $B71DD734 (vocfind) $B71D34A4 perform $B71D351C (search-wordlist) $B71D3FF4 find-name In fact, the 2nd `!` is never executed.