$ cat foo.scm
(printf "foo\n")

$ csc -O0 foo.scm
$ ./foo

Error: unbound variable: printf

        Call history:

        foo.scm:1: printf

$ csc -O1 foo.scm
$ ./foo
foo


$ cat foo.scm
(printf "foo\n")
(print read-string)
(print (feature? extras:))

$ csc -O0 foo.scm
$ ./foo

Error: unbound variable: printf

        Call history:

        foo.scm:1: printf               <--


$ csc -O1 foo.scm
$ ./foo
foo
#<unbound value>
#f


$ csc -O0 -k foo.scm && grep 'used units:' foo.c
   used units: library eval chicken_2dsyntax

$ csc -O1 -k foo.scm && grep 'used units:' foo.c
   used units: library eval chicken_2dsyntax