Here is how to get the current line number programmatically in PLT Scheme (via Jay):
#lang scheme
(define-syntax (current-line-number stx)
(quasisyntax/loc stx
'#,(syntax-line stx)))
(printf "~a: ~a~n" (current-line-number) 6)
(printf "~a: ~a~n" (current-line-number) 8)
(via plt)