From 438151f092f4d84133c190ba6a4dd886f5f8d49f Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Sun, 28 Feb 2016 21:33:53 -0500
Subject: [PATCH] Low-level implementation of file system.

---
 prospect/examples/actor/file-system-lll.rkt | 115 ++++++++++++++++++++
 prospect/examples/actor/file-system.rkt     |   1 +
 2 files changed, 116 insertions(+)
 create mode 100644 prospect/examples/actor/file-system-lll.rkt

diff --git a/prospect/examples/actor/file-system-lll.rkt b/prospect/examples/actor/file-system-lll.rkt
new file mode 100644
index 0000000..42aeb1f
--- /dev/null
+++ b/prospect/examples/actor/file-system-lll.rkt
@@ -0,0 +1,115 @@
+#lang prospect
+;; Toy file system, based on the example in the ESOP2016 submission.
+;; Low-level implementation.
+
+(require (only-in prospect [assert core:assert]))
+(require prospect/actor)
+(require prospect/drivers/timer)
+(require (only-in racket/port read-bytes-line-evt))
+(require (only-in racket/string string-trim string-split))
+(require racket/set)
+
+(struct file (name content) #:prefab)
+(struct save (file) #:prefab)
+(struct delete (name) #:prefab)
+
+(spawn-timer-driver)
+
+(define ((file-observation-event-handler name) e content)
+  (match e
+    [(? patch? p)
+     (if (set-empty? (project-assertions (patch-removed p) (observe (file (?!) ?))))
+         #f
+         (begin (printf "No remaining readers exist for ~v\n" name)
+                (quit)))]
+    [(message (save (file (== name) new-content)))
+     (transition new-content
+                 (patch-seq (retract (file name content))
+                            (core:assert (file name new-content))))]
+    [(message (delete (== name)))
+     (transition #f
+                 (patch-seq (retract (file name content))
+                            (core:assert (file name #f))))]
+    [_ #f]))
+
+(define (file-system-event-handler e files)
+  (match e
+    [(? patch? p)
+     (transition files
+                 (for/list [(name (project-assertions (patch-added p)
+                                                      (observe (file (?!) ?))))]
+                   (printf "At least one reader exists for ~v\n" name)
+                   (define initial-content (hash-ref files name #f))
+                   (spawn (file-observation-event-handler name)
+                          initial-content
+                          (patch-seq (core:assert (file name initial-content))
+                                     (sub (observe (file name ?)))
+                                     (sub (save (file name ?)))
+                                     (sub (delete name))))))]
+    [(message (save (file name new-content)))
+     (transition (hash-set files name new-content) '())]
+    [(message (delete name))
+     (transition (hash-remove files name) '())]
+    [_ #f]))
+
+     ;; (transition files
+     ;;             (for-trie/list [((observe (file $name _))
+     ;;                              (patch-added p))]
+     ;;               (let ()
+     ;;                 (printf "At least one reader exists for ~v\n" name)
+     ;;                 (define initial-content (hash-ref files name #f))
+     ;;                 (spawn (file-observation-event-handler name)
+     ;;                        initial-content
+     ;;                        (patch-seq (core:assert (file name initial-content))
+     ;;                                   (sub (observe (file name ?)))
+     ;;                                   (sub (save (file name ?)))
+     ;;                                   (sub (delete name)))))))]
+
+(spawn file-system-event-handler
+       (hash)
+       (patch-seq (sub (observe (file ? ?)))
+                  (sub (save (file ? ?)))
+                  (sub (delete ?))))
+
+(define (sleep sec)
+  (define timer-id (gensym 'sleep))
+  (until (message (timer-expired timer-id _))
+         #:init [(send! (set-timer timer-id (* sec 1000.0) 'relative))]))
+
+;; Shell
+(let ((e (read-bytes-line-evt (current-input-port) 'any)))
+  (define (print-prompt)
+    (printf "> ")
+    (flush-output))
+  (define reader-count 0)
+  (define (generate-reader-id)
+    (begin0 reader-count
+      (set! reader-count (+ reader-count 1))))
+  (actor (print-prompt)
+         (until (message (external-event e (list (? eof-object? _))) #:meta-level 1)
+                (on (message (external-event e (list (? bytes? $bs))) #:meta-level 1)
+                    (match (string-split (string-trim (bytes->string/utf-8 bs)))
+                      [(list "open" name)
+                       (define reader-id (generate-reader-id))
+                       (actor (printf "Reader ~a opening file ~v.\n" reader-id name)
+                              (until (message `(stop-watching ,name))
+                                     (on (asserted (file name $contents))
+                                         (printf "Reader ~a sees that ~v contains: ~v\n"
+                                                 reader-id
+                                                 name
+                                                 contents)))
+                              (printf "Reader ~a closing file ~v.\n" reader-id name))]
+                      [(list "close" name)
+                       (send! `(stop-watching ,name))]
+                      [(list* "write" name words)
+                       (send! (save (file name words)))]
+                      [(list "delete" name)
+                       (send! (delete name))]
+                      [_
+                       (printf "I'm afraid I didn't understand that.\n")
+                       (printf "Try: open filename\n")
+                       (printf "     close filename\n")
+                       (printf "     write filename some text goes here\n")
+                       (printf "     delete filename\n")])
+                    (sleep 0.1)
+                    (print-prompt)))))
diff --git a/prospect/examples/actor/file-system.rkt b/prospect/examples/actor/file-system.rkt
index 23f337c..0249651 100644
--- a/prospect/examples/actor/file-system.rkt
+++ b/prospect/examples/actor/file-system.rkt
@@ -1,5 +1,6 @@
 #lang prospect
 ;; Toy file system, based on the example in the ESOP2016 submission.
+;; prospect/actor implementation.
 
 (require prospect/actor)
 (require prospect/drivers/timer)