2.4.6 Examples of library usage

Consider a program using the procedure pretty-print to format some code, and suppose further that pretty printing is just a nice add–on (e.g. using write suffices, but pretty–printing is just prettier).

Vicare exports a good pretty–printing facility in its (vicare) library. However, since pretty-print is not a standard procedure, a program that uses it would be rendered unportable to other R6RS Scheme implementations.

The programmer can put the .vicare.sls extension to use in this situation, by writing two versions of a (pretty-printing) library: one for use by Vicare, and one portable for other implementations.

;; pretty-printing.vicare.sls --
;;
;; Can be used only by Vicare Scheme.

(library (pretty-printing)
  (export pretty-print)
  (import (only (vicare) pretty-print)))

;;; end of file

;; pretty-printing.sls --
;;
;; For any other Scheme implementation, portable though
;; not very pretty.

(library (pretty-printing)
  (export pretty-print)
  (import (rnrs))
  (define (pretty-print x port)
    (write x port)
    (newline port)))

;;; end of file