Issue 10

2010-11-01 +0000 · define-session-page

(use html-tags awful sandbox)

;; Here we define the REPL page.  It uses the session to store the
;; sandboxed environment.  By default, the `main-page-path' parameter
;; value is "/".
(define-session-page (main-page-path)
  (lambda ()

    ;; Create the sandbox environment (if it does not exist yet) and
    ;; store it in the user session.
    (unless ($session 'sandbox-env)
      ($session-set! 'sandbox-env
                     (make-safe-environment
                      parent: default-safe-environment
                      mutable: #t
                      extendable: #t)))

    ;; Here we set an ajax handler for the REPL expressions
    ;; submission.  When users change the REPL input widget (i.e., by
    ;; pressing ENTER), the contents of the text input field are
    ;; submitted and handled by the procedure given as the forth
    ;; argument to `ajax'.
    (ajax "eval" 'repl-input 'change
          (lambda ()

            ;; This binds the variable `repl-input' from the POST
            ;; method the the `repl-input' Scheme variable
            (let ((repl-input ($ 'repl-input)))

              ;; We'd better handle exceptions when trying to
              ;; evaluate the expressions given by users.
              (handle-exceptions
               exn
               ;; If something goes wrong, we print the error message
               ;; and the call chain.
               (<pre> convert-to-entities?: #t
                      (with-output-to-string
                        (lambda ()
                          (print-error-message exn)
                          (print-call-chain))))
               ;; Here we try to evaluate the given expression in the
               ;; sandboxed environment stored in the user session. 
               ;; The `repl-output' page div is updated with the result.
               (<pre> convert-to-entities?: #t
                      (safe-eval
                       (with-input-from-string repl-input read)
                       fuel: 100
                       allocation-limit: 100
                       environment: ($session 'sandbox-env))))))

          ;; Here we pass the contents of the text input to the ajax
          ;; handler.  The default HTTP method used by `ajax' is POST.
          arguments: `((repl-input . "$('#repl-input').val()"))

          ;; The output of the ajax handler updates the `repl-output'
          ;; page div.
          target: "repl-output")

    ;; Here's what is displayed to users
    (++ (<h1> "Sandboxed Chicken web REPL")
        (<input> type: "text" id: "repl-input")
        (<div> id: "repl-output")))

  ;; This tells `define-session-page' to link the page to JQuery
  use-ajax: #t)

Issue 10

0. Introduction

1. The Hatching Farm

2. Yolklore

3. Chicken Talk

4. Omelette Recipes - Tips and Tricks

5. About the Chicken Gazette