Reimplement live-reload module.

* sly/live-reload.scm (watch-files): New procedure.
  (live-reload): Rename to...
  (with-live-reload): This.
* doc/api/utils.tex ("Live Reloading"): Update docs.

2 files changed, 67 insertions, 26 deletions

diff --git a/doc/api/utils.texi b/doc/api/utils.texi
index 4858010..4c7c39f 100644
--- a/doc/api/utils.texi
+++ b/doc/api/utils.texi
@@ -42,12 +42,38 @@ Abort from the error handling loop prompt and resume the game loop.
 (use-modules (sly utils live-reload))
 @end example
 
-The live-reload module enables Sly programs to react to changes in the
-file system and reload assets automatically, which is useful when
-using external programs such as an image editor or map editor.  This
-makes it easy to see the changes made to game assets quickly.
+The @code{(sly live-reload)} module enables Sly programs to react to
+changes in the file system and reload assets automatically, which is
+useful when using external programs such as an image editor or map
+editor.  Live reloading reduces the time and effort needed to see the
+changes made to game assets.
 
-@defun live-reload @var{proc} [@var{polling-interval}]
+The following example uses the @code{with-live-reload} procedure to
+create a texturing loading procedure that automatically reloads
+textures when their associated file on disk changes:
+
+@example
+(use-modules (sly live-reload)
+             (sly signal)
+             (sly texture))
+
+(define load-texture/live (with-live-reload load-texture))
+
+(define-signal fox (load-texture/live "fox.png"))
+@end example
+
+The more generic @code{watch-files} procedure can be used to implement
+new types of live reloading procedures.
+
+@deffn {Scheme Procedure} watch-files @var{files} @var{thunk} [@var{polling-interval}]
+Watch @var{files}, a list of file names, and apply @var{thunk} each
+time one of them changes.  A signal (@pxref{Signals}) is returned that
+contains the current result of @var{thunk}.  The
+@var{polling-interval} flag determines how often @var{files} are
+polled for changes, defaulting to two seconds.
+@end deffn
+
+@deffn {Scheme Procedure} with-live-reload @var{proc} [@var{polling-interval}]
 Return a new procedure that re-applies @code{proc} whenever the
 associated file is modified.  The new procedure returns a signal
 (@pxref{Signals}) that contains the return value of @code{proc}.  The
@@ -55,7 +81,7 @@ first argument to @code{proc} must be a file name string.
 
 A simple polling method is used to test for updates.  Files are polled
 every @code{polling-interval} ticks (120 by default).
-@end defun
+@end deffn
 
 @node Miscellaneous-Utilities
 @subsection Miscellaneous
diff --git a/sly/live-reload.scm b/sly/live-reload.scm
index f354fda..cb40e7c 100644
--- a/sly/live-reload.scm
+++ b/sly/live-reload.scm
@@ -26,9 +26,40 @@
   #:use-module (sly agenda)
   #:use-module (sly coroutine)
   #:use-module (sly signal)
-  #:export (live-reload))
+  #:export (watch-files
+            with-live-reload))
 
-(define* (live-reload proc #:optional (polling-interval 120))
+(define* (watch-files files thunk #:optional (polling-interval 120))
+  "Watch FILES, a list of file names, and apply THUNK each time one of
+them changes.  A signal is returned that contains the current result
+of THUNK.  The POLLING-INTERVAL flag determines how often FILES are
+polled for changes, defaulting to two seconds."
+  (define (current-mtime file-name)
+    (let ((info (stat file-name)))
+      (max (stat:mtime info) (stat:ctime info))))
+
+  (define (max-current-mtime)
+    (and (every file-exists? files)
+         (reduce max 0 (map current-mtime files))))
+
+  (let ((asset (make-signal (thunk))))
+    (coroutine
+     (let loop ((last-mtime (max-current-mtime)))
+       (wait polling-interval)
+       (let ((mtime (max-current-mtime)))
+         (when (cond
+                ;; Some files do not exist anymore, can't reload.
+                ((not mtime) #f)
+                ;; Some files were missing, but are back now.
+                ((and mtime (not last-mtime)) #t)
+                ;; All the files exist and existed last time, too, so
+                ;; check if they have been modified since last time.
+                (else (> mtime last-mtime)))
+           (signal-set! asset (thunk)))
+         (loop mtime))))
+    asset))
+
+(define* (with-live-reload proc #:optional (polling-interval 120))
   "Return a new procedure that re-applies PROC whenever the associated
 file is modified.  The new procedure returns a signal that contains
 the return value of PROC.  The first argument to PROC must be a
@@ -37,21 +68,5 @@ file name string.
 A simple polling method is used to test for updates.  Files are polled
 every POLLING-INTERVAL ticks (120 by default)."
   (lambda (file-name . args)
-    (define (load-asset)
-      (apply proc file-name args))
-
-    (define (current-mtime)
-      (let ((info (stat file-name)))
-        (max (stat:mtime info) (stat:ctime info))))
-
-    (let ((asset (make-signal (load-asset))))
-      (coroutine
-       (let loop ((last-mtime (current-mtime)))
-         (wait polling-interval)
-         (let ((mtime (if (file-exists? file-name)
-                          (current-mtime)
-                          last-mtime)))
-           (when (> mtime last-mtime)
-             (signal-set! asset (load-asset)))
-           (loop mtime))))
-      asset)))
+    (watch-files (list file-name)
+                 (lambda () (apply proc file-name args)))))