Real-World Scheme

51.1 Scripting

#!/usr/bin/env -S guile -s
!#
;; count-lines.scm: count lines in the files given on the command line
(use-modules (ice-9 textual-ports))
(for-each
  (lambda (file)
    (let ((n (length (string-split (call-with-input-file file get-string-all) #\newline))))
      (format #t "~a: ~a lines~%" file (- n 1))))
  (cdr (command-line)))

51.2 Notable Systems Built with Scheme

GNU Guix / Shepherd Functional package management, OS configuration, init system Accounting (reports) GIMP Script-Fu Image editing automation Racket (CS) Naughty Dog games Racket-based DSLs, GOAL (Lisp) Spritely Goblins / Hoot Distributed objects, WebAssembly (embeddable Scheme) Snd, Common Music, audio Static site generator

51.3 Web Development

Other options: Guile Artanis (web framework), CHICKEN Spiffy/Awful, Racket web-server, Gerbil's HTTP server, and SXML for HTML/XML as s-expressions:

;; Guile's built-in web server
(use-modules (web server) (web request) (web response) (web uri))
(define (handler request body)
  (let ((path (uri-path (request-uri request))))
    (values '((content-type . (text/plain)))
            (string-append "Hello from Guile! You requested " path))))
(run-server handler 'http '(#:port 8080))

;; SXML: XML/HTML as lists
'(html (head (title "Page")) (body (h1 "Hello") (p (@ (class "intro")) "Text")))
;; Guile: (use-modules (sxml simple)) (sxml->xml tree)

51.4 Embedding Scheme as an Extension Language

Applications embed Guile, Chibi, S7, or TinyScheme to let users script them, as Emacs does with Emacs Lisp. Expose host functions to Scheme, run user scripts in restricted environments ((environment ...) with only safe bindings), and call Scheme callbacks from C.