rmeta-slot: New module for recursive meta-slot access.

This is an abstraction around the core idea driving the actor actions
system.  It turns out I need this abstraction for mudsync as well, so
I'm breaking it out.  Pleasantly, it should be much faster now, since
a cache is built for each class regarding what key should resolve to
what value.

* 8sync/rmeta-slot.scm:
* tests/test-rmeta-slot.scm: New modules.
* Makefile.am: Add them.

3 files changed, 182 insertions, 1 deletions

diff --git a/8sync/rmeta-slot.scm b/8sync/rmeta-slot.scm
new file mode 100644
index 0000000..de85ee9
--- /dev/null
+++ b/8sync/rmeta-slot.scm
@@ -0,0 +1,113 @@
+;;; 8sync --- Asynchronous programming for Guile
+;;; Copyright © 2016, 2017 Christopher Allan Webber <cwebber@dustycloud.org>
+;;;
+;;; This file is part of 8sync.
+;;;
+;;; 8sync is free software: you can redistribute it and/or modify it
+;;; under the terms of the GNU Lesser General Public License as
+;;; published by the Free Software Foundation, either version 3 of the
+;;; License, or (at your option) any later version.
+;;;
+;;; 8sync is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public
+;;; License along with 8sync.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (8sync rmeta-slot)
+  #:use-module (oop goops)
+  #:use-module (srfi srfi-9)
+  #:use-module (ice-9 match)
+
+  #:export (make-rmeta-slot
+            maybe-build-rmeta-slot-cache!
+            class-rmeta-ref))
+
+;;; This module is for rmeta-slots, aka a recursive-meta-slot.
+;;;
+;;; Recursive meta-slots are recursive because we walk down the
+;;; inheritance list until we find a match, and meta because they
+;;; are sort of "slots" of their own... alists, rather, where you
+;;; are searching for the right key.
+;;;
+;;; Recursive meta-slots have their own cache so access is
+;;; reasonably fast.
+;;;
+;;; A recursive meta-slot definition looks something like this:
+;;;
+;;;   ;; Define a class with a meta-slot
+;;;   (define-class <kah-lassy> ()
+;;;     (entries #:allocation #:each-subclass
+;;;              #:init-value
+;;;              (make-rmeta-slot
+;;;               `((foo . "bar")
+;;;                 (baz . "basil")))))
+;;;
+;;;   ;; Access values
+;;;   (class-rmeta-ref <kah-lassy> 'entries 'foo) => "bar"
+;;;   (class-rmeta-ref <kah-lassy> 'entries 'baz) => "basil"
+;;;
+;;;   ;; Define a subclass
+;;;   (define-class <sub-lassy> (<kah-lassy>)
+;;;     (entries #:allocation #:each-subclass
+;;;              #:init-value
+;;;              (make-rmeta-slot
+;;;               `((foo . "foo2")
+;;;                 (peanut . "gallery")))))
+;;;
+;;;   ;; Access values, and inheritance is preserved
+;;;   (class-rmeta-ref <sub-lassy> 'entries 'foo) => "foo2"
+;;;   (class-rmeta-ref <sub-lassy> 'entries 'peanut) => "gallery"
+;;;   (class-rmeta-ref <sub-lassy> 'entries 'baz) => "basil"
+
+(define-record-type <rmeta-slot>
+  (%make-rmeta-slot table cache)
+  rmeta-slot?
+  (table rmeta-slot-table)
+  (cache rmeta-slot-cache set-rmeta-slot-cache!))
+
+(define (make-rmeta-slot table)
+  (%make-rmeta-slot table #f))
+
+;; Immutable and unique
+(define %the-nothing (cons '*the* '*nothing*))
+
+(define (maybe-build-rmeta-slot-cache! class slot-name
+                                       equals? cache-set! cache-ref)
+  "Build the rmeta slot cache, if it isn't built already."
+  (define rmeta-slot
+    (class-slot-ref class slot-name))
+  (define (build-cache)
+    (define cache (make-hash-table))
+    (for-each
+     (lambda (this-class)
+       (and (class-slot-definition this-class slot-name)
+            (class-slot-ref this-class slot-name)
+            (let ((this-rmeta (class-slot-ref this-class slot-name)))
+              (for-each (match-lambda
+                          ((key . val)
+                           ;; Add this value to the list if we haven't yet seen
+                           ;; such a definition before
+                           (when (eq? (cache-ref cache key %the-nothing)
+                                      %the-nothing)
+                             (cache-set! cache key val))))
+                        (rmeta-slot-table this-rmeta)))))
+     (class-precedence-list class))
+    cache)
+  ;; If it's alreayd built, this is a no-op.
+  (when (not (rmeta-slot-cache rmeta-slot))
+    (set-rmeta-slot-cache! rmeta-slot (build-cache))))
+
+(define* (class-rmeta-ref class slot-name key
+                          #:key (equals? eq?)
+                          (cache-set! hashq-set!)
+                          (cache-ref hashq-ref)
+                          dflt)
+  "Search heirarchy of CLASS through the rmeta-slot named SLOT-NAME for
+value matching KEY.  This also calls maybe-build-rmeta-slot-cache! as a side
+effect."
+  (maybe-build-rmeta-slot-cache! class slot-name
+                                 equals? cache-set! cache-ref)
+  (cache-ref (rmeta-slot-cache (class-slot-ref class slot-name)) key dflt))
diff --git a/Makefile.am b/Makefile.am
index d0dd1a4..926d755 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -51,6 +51,7 @@ SOURCES =  \
 	8sync/actors.scm				\
 	8sync/debug.scm					\
 	8sync/ports.scm					\
+	8sync/rmeta-slot.scm				\
 	8sync/contrib/base64.scm			\
 	8sync/contrib/sha-1.scm				\
 	8sync/systems/irc.scm				\
@@ -63,7 +64,8 @@ SOURCES =  \
 
 TESTS =							\
 	tests/test-agenda.scm				\
-	tests/test-actors.scm
+	tests/test-actors.scm				\
+	tests/test-rmeta-slot.scm
 
 TEST_EXTENSIONS = .scm
 
diff --git a/tests/test-rmeta-slot.scm b/tests/test-rmeta-slot.scm
new file mode 100644
index 0000000..0fd4b6f
--- /dev/null
+++ b/tests/test-rmeta-slot.scm
@@ -0,0 +1,66 @@
+;;; 8sync --- Asynchronous programming for Guile
+;;; Copyright (C) 2017 Christopher Allan Webber <cwebber@dustycloud.org>
+;;;
+;;; This file is part of 8sync.
+;;;
+;;; 8sync is free software: you can redistribute it and/or modify it
+;;; under the terms of the GNU Lesser General Public License as
+;;; published by the Free Software Foundation, either version 3 of the
+;;; License, or (at your option) any later version.
+;;;
+;;; 8sync is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public
+;;; License along with 8sync.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (tests test-rmeta-slot)
+  #:use-module (srfi srfi-64)
+  #:use-module (8sync rmeta-slot)
+  #:use-module (oop goops)
+  #:use-module (tests utils))
+
+(test-begin "test-rmeta-slot")
+
+;; Define a class
+(define-class <kah-lassy> ()
+  (entries #:allocation #:each-subclass
+           #:init-value
+           (make-rmeta-slot
+            `((foo . "bar")
+              (baz . "basil")))))
+
+(test-equal "bar"
+    (class-rmeta-ref <kah-lassy> 'entries 'foo))
+(test-equal "basil"
+    (class-rmeta-ref <kah-lassy> 'entries 'baz))
+
+;; Define a subclass
+
+(define-class <sub-lassy> (<kah-lassy>)
+  (entries #:allocation #:each-subclass
+           #:init-value
+           (make-rmeta-slot
+            `((foo . "foo2")
+              (peanut . "gallery")))))
+
+;; Access values, and inheritance is preserved
+(test-equal "foo2"
+  (class-rmeta-ref <sub-lassy> 'entries 'foo))
+(test-equal "gallery"
+  (class-rmeta-ref <sub-lassy> 'entries 'peanut))
+(test-equal "basil"
+  (class-rmeta-ref <sub-lassy> 'entries 'baz))
+
+;; Not defined
+(test-equal #f
+  (class-rmeta-ref <sub-lassy> 'entries 'not-defined))
+;; Not defined, with default
+(test-equal "no-way"
+  (class-rmeta-ref <sub-lassy> 'entries 'not-defined
+                   #:dflt "no-way"))
+
+(test-end "test-rmeta-slot")
+(test-exit)