cat a.scm
(declare (unit a))
(define zooi 'a)

$ cat b.scm
(declare (uses a))
(print zooi)

$ csc -c a.scm b.scm ; csc -s a.o b.o -o c.so

$ csi
#;1> (load "c.so")  
; loading c.so ...
#;2> (print zooi)  
a
#;3> (exit)  
Warning: "exit" called while processing on-exit tasks
#;4>   

[13:24:06] ckeen@necronomicon:~
; csc -c a.scm b.scm     
[13:24:47] ckeen@necronomicon:~
; csc -s a.o b.o -o c.so 
b.o(.text+0x88): In function `C_toplevel':
: multiple definition of `C_toplevel'
a.o(.text+0x88): first defined here
b.o(.text+0x3e8): In function `main':
: multiple definition of `main'
a.o(.text+0x3e8): first defined here
collect2: ld returned 1 exit status