cheme@(guile-user)> (define (reverse wd) (if (equal? wd "") "" (word (reverse (bf wd)) (first wd)))) scheme@(guile-user)> (use-modules (system vm trace)) scheme@(guile-user)> (trace-calls-to-procedure reverse #:prefix "XXX: ") $1 = # scheme@(guile-user)> (reverse 'asdf) $2 = fdsa scheme@(guile-user)> (call-with-trace (lambda () (reverse 'asdf)) #:calls? #f) XXX: (reverse asdf) XXX: | (reverse sdf) XXX: | | (reverse df) XXX: | | | (reverse f) XXX: | | | | (reverse "") ice-9/boot-9.scm:1669:16: In procedure raise-exception: Wrong number of arguments to # Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. scheme@(guile-user) [1]> ,q scheme@(guile-user)> (call-with-trace (lambda () (reverse 'asdf)) #:calls? #f) ice-9/boot-9.scm:1669:16: In procedure raise-exception: Wrong number of arguments to # Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. scheme@(guile-user) [1]>