Why is it needed to discard void return value from c function?

[luntik2012]

written just 
    
    
    quit
    
    
    Run

c-function returns void. nim wrapper declared in sources like this 
    
    
    proc quit*(errorcode: int = QuitSuccess) {.
      magic: "Exit", importc: "exit", header: "<stdlib.h>", noreturn.}
    
    
    Run

but 
    
    
    murder.nim(9, 3) Error: expression 'quit' is of type 'None' and has to be 
discarded; start of expression here: murder.nim(8, 2)
    
    
    Run

wtf?