guile-examples/web-development/example-03-serve-static-assets/logging.scm

(define-module (logging)
  #:export (debug))


(define displayln
  (lambda* (#:key (output-port (current-output-port)) (verbose #t) . msgs)
    (when verbose
      (display (string-append
                (string-join
                 (map (lambda (msg) (simple-format #f "~a" msg)) msgs)
                 " ") "\n")
               output-port))))


;; alias for displayln
(define debug displayln)