Prototypal inheritance of sprite-local variables

(experimental) slotwise inheritance à la Henry Lieberman for
sprite-local variables.

see
http://web.media.mit.edu/~lieber/Lieberary/OOP/Delegation/Delegation.htm
l

Let a sprite inherit another sprite’s local variables by making it the
“parent” in the sprite-icon’s context menu (the button icon in the
sprite corral underneath the stage). The child not only inherits the
variable slot but also - dynamically - the parent variable’s value.
Changing the parent’s variable value also changes it for every child.
If a child uses SET or CHANGE on an inherited variable it automatically
“shadows” it with its own value, thereby stopping dynamic participation
in the parent slot’s value (in effect dis-inheriting that slot).
Deleting a shadowed variable slot once again reinstates its inheritance
status.

inherited variables are shown as “ghosted” both in the child’s
variables palette and in such stage watchers. “Shadowing” them
un-ghosts both the variable blob template in the palette and the
watcher onstage (if any). Deleting a shadowed variable once again
ghosts the watcher and the palette block template.

Delete a (shadowed) variable either via the “Delete a variable” button
in the IDE or using the new “Delete” block in the variables category

9 files changed, 335 insertions, 63 deletions

diff --git a/blocks.js b/blocks.js
index aef09da..711976f 100644
--- a/blocks.js
+++ b/blocks.js
@@ -155,7 +155,7 @@ DialogBoxMorph, BlockInputFragmentMorph, PrototypeHatBlockMorph, Costume*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.blocks = '2015-March-09';
+modules.blocks = '2015-March-21';
 
 
 var SyntaxElementMorph;
@@ -3016,6 +3016,12 @@ BlockMorph.prototype.alternateBlockColor = function () {
     this.fixChildrensBlockColor(true); // has issues if not forced
 };
 
+BlockMorph.prototype.ghost = function () {
+    this.setColor(
+        SpriteMorph.prototype.blockColor[this.category].lighter(35)
+    );
+};
+
 BlockMorph.prototype.fixLabelColor = function () {
     if (this.zebraContrast > 0 && this.category) {
         var clr = SpriteMorph.prototype.blockColor[this.category];
@@ -3096,6 +3102,10 @@ BlockMorph.prototype.mouseClickLeft = function () {
     }
 };
 
+BlockMorph.prototype.reactToTemplateCopy = function () {
+    this.forceNormalColoring();
+};
+
 // BlockMorph thumbnail
 
 BlockMorph.prototype.thumbnail = function (scale, clipWidth, noShadow) {
diff --git a/gui.js b/gui.js
index 50f3cb2..4cd2a9b 100644
--- a/gui.js
+++ b/gui.js
@@ -69,7 +69,7 @@ SpeechBubbleMorph*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.gui = '2015-March-15';
+modules.gui = '2015-March-21';
 
 // Declarations
 
@@ -2598,7 +2598,7 @@ IDE_Morph.prototype.aboutSnap = function () {
         module, btn1, btn2, btn3, btn4, licenseBtn, translatorsBtn,
         world = this.world();
 
-    aboutTxt = 'Snap! 4.0\nBuild Your Own Blocks\n\n--- rc ---\n\n'
+    aboutTxt = 'Snap! 4.1 (OOP)\nBuild Your Own Blocks\n\n--- dev ---\n\n'
         + 'Copyright \u24B8 2015 Jens M\u00F6nig and '
         + 'Brian Harvey\n'
         + 'jens@moenig.org, bh@cs.berkeley.edu\n\n'
@@ -5182,7 +5182,7 @@ function SpriteIconMorph(aSprite, aTemplate) {
 }
 
 SpriteIconMorph.prototype.init = function (aSprite, aTemplate) {
-    var colors, action, query, myself = this;
+    var colors, action, query, hover, myself = this;
 
     if (!aTemplate) {
         colors = [
@@ -5212,6 +5212,11 @@ SpriteIconMorph.prototype.init = function (aSprite, aTemplate) {
         return false;
     };
 
+    hover = function () {
+        if (!aSprite.exemplar) {return null; }
+        return (localize('parent' + ':\n' + aSprite.exemplar.name));
+    };
+
     // additional properties:
     this.object = aSprite || new SpriteMorph(); // mandatory, actually
     this.version = this.object.version;
@@ -5227,7 +5232,7 @@ SpriteIconMorph.prototype.init = function (aSprite, aTemplate) {
         this.object.name, // label string
         query, // predicate/selector
         null, // environment
-        null, // hint
+        hover, // hint
         aTemplate // optional, for cached background images
     );
 
@@ -5398,6 +5403,7 @@ SpriteIconMorph.prototype.userMenu = function () {
     menu.addItem("duplicate", 'duplicateSprite');
     menu.addItem("delete", 'removeSprite');
     menu.addLine();
+    menu.addItem("parent...", 'chooseExemplar');
     if (this.object.anchor) {
         menu.addItem(
             localize('detach from') + ' ' + this.object.anchor.name,
@@ -5432,6 +5438,10 @@ SpriteIconMorph.prototype.exportSprite = function () {
     this.object.exportSprite();
 };
 
+SpriteIconMorph.prototype.chooseExemplar = function () {
+    this.object.chooseExemplar();
+};
+
 SpriteIconMorph.prototype.showSpriteOnStage = function () {
     this.object.showOnStage();
 };
diff --git a/history.txt b/history.txt
index b53e59c..e02d368 100755
--- a/history.txt
+++ b/history.txt
@@ -2476,3 +2476,7 @@ ______
 ------
 * Store: fixed #743
 * GUI, html: switch from beta to release candidate
+
+150321
+------
+* OOP: Prototypal inheritance of sprite-local variables
diff --git a/morphic.js b/morphic.js
index 9616897..359e552 100644
--- a/morphic.js
+++ b/morphic.js
@@ -8,7 +8,7 @@
     written by Jens Mönig
     jens@moenig.org
 
-    Copyright (C) 2014 by Jens Mönig
+    Copyright (C) 2015 by Jens Mönig
 
     This file is part of Snap!.
 
@@ -527,6 +527,12 @@
     a duplicate of the template whose "isDraggable" flag is true and
     whose "isTemplate" flag is false, in other words: a non-template.
 
+    When creating a copy from a template, the copy's
+    
+        reactToTemplateCopy
+
+    is invoked, if it is present.
+
     Dragging is indicated by adding a drop shadow to the morph in hand.
     If a morph follows the hand without displaying a drop shadow it is
     merely being moved about without changing its parent (owner morph),
@@ -1020,9 +1026,10 @@
     programming hero.
 
     I have originally written morphic.js in Florian Balmer's Notepad2
-    editor for Windows and later switched to Apple's Dashcode. I've also
-    come to depend on both Douglas Crockford's JSLint, Mozilla's Firebug
-    and Google's Chrome to get it right.
+    editor for Windows, later switched to Apple's Dashcode and later
+    still to Apple's Xcode. I've also come to depend on both Douglas
+    Crockford's JSLint, Mozilla's Firebug and Google's Chrome to get
+    it right.
 
 
     IX. contributors
@@ -1041,7 +1048,7 @@
 /*global window, HTMLCanvasElement, getMinimumFontHeight, FileReader, Audio,
 FileList, getBlurredShadowSupport*/
 
-var morphicVersion = '2014-December-05';
+var morphicVersion = '2015-March-21';
 var modules = {}; // keep track of additional loaded modules
 var useBlurredShadows = getBlurredShadowSupport(); // check for Chrome-bug
 
@@ -8060,7 +8067,7 @@ TriggerMorph.prototype.init = function (
     this.environment = environment || null;
     this.labelString = labelString || null;
     this.label = null;
-    this.hint = hint || null;
+    this.hint = hint || null; // null, String, or Function
     this.fontSize = fontSize || MorphicPreferences.menuFontSize;
     this.fontStyle = fontStyle || 'sans-serif';
     this.highlightColor = new Color(192, 192, 192);
@@ -8209,10 +8216,11 @@ TriggerMorph.prototype.triggerDoubleClick = function () {
 // TriggerMorph events:
 
 TriggerMorph.prototype.mouseEnter = function () {
+    var contents = this.hint instanceof Function ? this.hint() : this.hint;
     this.image = this.highlightImage;
     this.changed();
-    if (this.hint) {
-        this.bubbleHelp(this.hint);
+    if (contents) {
+        this.bubbleHelp(contents);
     }
 };
 
@@ -9683,6 +9691,9 @@ HandMorph.prototype.processMouseMove = function (event) {
                 morph = this.morphToGrab.fullCopy();
                 morph.isTemplate = false;
                 morph.isDraggable = true;
+                if (morph.reactToTemplateCopy) {
+                    morph.reactToTemplateCopy();
+                }
                 this.grab(morph);
                 this.grabOrigin = this.morphToGrab.situation();
             }
diff --git a/objects.js b/objects.js
index 1fe1309..56e5806 100644
--- a/objects.js
+++ b/objects.js
@@ -125,7 +125,7 @@ PrototypeHatBlockMorph*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.objects = '2015-February-28';
+modules.objects = '2015-March-21';
 
 var SpriteMorph;
 var StageMorph;
@@ -1103,6 +1103,13 @@ SpriteMorph.prototype.initBlocks = function () {
             spec: 'script variables %scriptVars'
         },
 
+        // inheritance - experimental
+        doDeleteAttr: {
+            type: 'command',
+            category: 'variables',
+            spec: 'delete %var'
+        },
+
         // Lists
         reportNewList: {
             type: 'reporter',
@@ -1348,11 +1355,13 @@ SpriteMorph.prototype.init = function (globals) {
                             'confetti': 0
                          };
 
+    // sprite inheritance
+    this.exemplar = null;
+
     SpriteMorph.uber.init.call(this);
 
     this.isDraggable = true;
     this.isDown = false;
-
     this.heading = 90;
     this.changed();
     this.drawNew();
@@ -1642,7 +1651,8 @@ SpriteMorph.prototype.variableBlock = function (varName) {
 
 SpriteMorph.prototype.blockTemplates = function (category) {
     var blocks = [], myself = this, varNames, button,
-        cat = category || 'motion', txt;
+        cat = category || 'motion', txt,
+        inheritedVars = this.inheritedVariableNames();
 
     function block(selector) {
         if (StageMorph.prototype.hiddenPrimitives[selector]) {
@@ -1657,6 +1667,9 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         var newBlock = SpriteMorph.prototype.variableBlock(varName);
         newBlock.isDraggable = false;
         newBlock.isTemplate = true;
+        if (contains(inheritedVars, varName)) {
+            newBlock.ghost();
+        }
         return newBlock;
     }
 
@@ -1705,15 +1718,16 @@ SpriteMorph.prototype.blockTemplates = function (category) {
     }
 
     function addVar(pair) {
+        var ide;
         if (pair) {
-            if (myself.variables.silentFind(pair[0])) {
+            if (myself.isVariableNameInUse(pair[0])) {
                 myself.inform('that name is already in use');
             } else {
+                ide = myself.parentThatIsA(IDE_Morph);
                 myself.addVariable(pair[0], pair[1]);
                 myself.toggleVariableWatcher(pair[0], pair[1]);
-                myself.blocksCache[cat] = null;
-                myself.paletteCache[cat] = null;
-                myself.parentThatIsA(IDE_Morph).refreshPalette();
+                ide.flushBlocksCache('variables'); // b/c of inheritance
+                ide.refreshPalette();
             }
         }
     }
@@ -2028,7 +2042,7 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         button.showHelp = BlockMorph.prototype.showHelp;
         blocks.push(button);
 
-        if (this.variables.allNames().length > 0) {
+        if (this.deletableVariableNames().length > 0) {
             button = new PushButtonMorph(
                 null,
                 function () {
@@ -2037,7 +2051,7 @@ SpriteMorph.prototype.blockTemplates = function (category) {
                         null,
                         myself
                     );
-                    myself.variables.allNames().forEach(function (name) {
+                    myself.deletableVariableNames().forEach(function (name) {
                         menu.addItem(name, name);
                     });
                     menu.popUpAtHand(myself.world());
@@ -2067,6 +2081,13 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         blocks.push(block('doHideVar'));
         blocks.push(block('doDeclareVariables'));
 
+    // inheritance:
+
+        blocks.push('-');
+        blocks.push(block('doDeleteAttr'));
+
+    ///////////////////////////////
+
         blocks.push('=');
 
         blocks.push(block('reportNewList'));
@@ -2491,7 +2512,7 @@ SpriteMorph.prototype.searchBlocks = function () {
 SpriteMorph.prototype.addVariable = function (name, isGlobal) {
     var ide = this.parentThatIsA(IDE_Morph);
     if (isGlobal) {
-        this.variables.parentFrame.addVar(name);
+        this.globalVariables().addVar(name);
         if (ide) {
             ide.flushBlocksCache('variables');
         }
@@ -2503,7 +2524,10 @@ SpriteMorph.prototype.addVariable = function (name, isGlobal) {
 
 SpriteMorph.prototype.deleteVariable = function (varName) {
     var ide = this.parentThatIsA(IDE_Morph);
-    this.deleteVariableWatcher(varName);
+    if (!contains(this.inheritedVariableNames(true), varName)) {
+        // check only shadowed variables
+        this.deleteVariableWatcher(varName);
+    }
     this.variables.deleteVar(varName);
     if (ide) {
         ide.flushBlocksCache('variables'); // b/c the var could be global
@@ -3643,6 +3667,7 @@ SpriteMorph.prototype.reportThreadCount = function () {
 
 SpriteMorph.prototype.findVariableWatcher = function (varName) {
     var stage = this.parentThatIsA(StageMorph),
+        globals = this.globalVariables(),
         myself = this;
     if (stage === null) {
         return null;
@@ -3652,7 +3677,7 @@ SpriteMorph.prototype.findVariableWatcher = function (varName) {
         function (morph) {
             return morph instanceof WatcherMorph
                     && (morph.target === myself.variables
-                            || morph.target === myself.variables.parentFrame)
+                            || morph.target === globals)
                     && morph.getter === varName;
         }
     );
@@ -3660,6 +3685,7 @@ SpriteMorph.prototype.findVariableWatcher = function (varName) {
 
 SpriteMorph.prototype.toggleVariableWatcher = function (varName, isGlobal) {
     var stage = this.parentThatIsA(StageMorph),
+        globals = this.globalVariables(),
         watcher,
         others;
     if (stage === null) {
@@ -3679,12 +3705,12 @@ SpriteMorph.prototype.toggleVariableWatcher = function (varName, isGlobal) {
 
     // if no watcher exists, create a new one
     if (isNil(isGlobal)) {
-        isGlobal = contains(this.variables.parentFrame.names(), varName);
+        isGlobal = contains(globals.names(), varName);
     }
     watcher = new WatcherMorph(
         varName,
         this.blockColor.variables,
-        isGlobal ? this.variables.parentFrame : this.variables,
+        isGlobal ? globals : this.variables,
         varName
     );
     watcher.setPosition(stage.position().add(10));
@@ -4110,6 +4136,118 @@ SpriteMorph.prototype.restoreLayers = function () {
     this.layers = null;
 };
 
+// SpriteMorph inheritance - general
+
+SpriteMorph.prototype.chooseExemplar = function () {
+    var stage = this.parentThatIsA(StageMorph),
+        myself = this,
+        other = stage.children.filter(function (m) {
+            return m instanceof SpriteMorph &&
+                (!contains(m.allExemplars(), myself));
+        }),
+        menu;
+    menu = new MenuMorph(
+        function (aSprite) {myself.setExemplar(aSprite); },
+        localize('current parent') +
+            ':\n' +
+            (this.exemplar ? this.exemplar.name : localize('none'))
+    );
+    other.forEach(function (eachSprite) {
+        menu.addItem(eachSprite.name, eachSprite);
+    });
+    menu.addLine();
+    menu.addItem(localize('none'), null);
+    menu.popUpAtHand(this.world());
+};
+
+SpriteMorph.prototype.setExemplar = function (another) {
+    var ide = this.parentThatIsA(IDE_Morph);
+    this.exemplar = another;
+    if (isNil(another)) {
+        this.variables.parentFrame = (this.globalVariables());
+    } else {
+        this.variables.parentFrame = (another.variables);
+    }
+    if (ide) {
+        ide.flushBlocksCache('variables');
+        ide.refreshPalette();
+    }
+};
+
+SpriteMorph.prototype.allExemplars = function () {
+    // including myself
+    var all = [],
+        current = this;
+    while (!isNil(current)) {
+        all.push(current);
+        current = current.exemplar;
+    }
+    return all;
+};
+
+SpriteMorph.prototype.specimens = function () {
+    // without myself
+    var myself = this;
+    return this.siblings().filter(function (m) {
+        return m instanceof SpriteMorph && (m.exemplar === myself);
+    });
+};
+
+SpriteMorph.prototype.allSpecimens = function () {
+    // without myself
+    var myself = this;
+    return this.siblings().filter(function (m) {
+        return m instanceof SpriteMorph && contains(m.allExemplars(), myself);
+    });
+};
+
+// SpriteMorph inheritance - variables
+
+SpriteMorph.prototype.isVariableNameInUse = function (vName) {
+    if (contains(this.variables.names(), vName)) {return true; }
+    return contains(this.globalVariables().names(), vName);
+};
+
+SpriteMorph.prototype.globalVariables = function () {
+    var current = this.variables.parentFrame;
+    while (current.owner) {
+        current = current.parentFrame;
+    }
+    return current;
+};
+
+SpriteMorph.prototype.shadowVar = function (name, value) {
+    var ide = this.parentThatIsA(IDE_Morph);
+    this.variables.addVar(name, value);
+    ide.flushBlocksCache('variables');
+    ide.refreshPalette();
+};
+
+SpriteMorph.prototype.inheritedVariableNames = function (shadowedOnly) {
+    var names = [],
+        own = this.variables.names(),
+        current = this.variables.parentFrame;
+
+    function test(each) {
+        return shadowedOnly ? contains(own, each) : !contains(own, each);
+    }
+
+    while (current.owner instanceof SpriteMorph) {
+        names.push.apply(
+            names,
+            current.names().filter(test)
+        );
+        current = current.parentFrame;
+    }
+    return names;
+};
+
+SpriteMorph.prototype.deletableVariableNames = function () {
+    return this.variables.names().concat(
+        this.globalVariables().names()
+    );
+};
+
 // SpriteMorph highlighting
 
 SpriteMorph.prototype.addHighlight = function (oldHighlight) {
@@ -4966,7 +5104,7 @@ StageMorph.prototype.blockTemplates = function (category) {
 
     function addVar(pair) {
         if (pair) {
-            if (myself.variables.silentFind(pair[0])) {
+            if (myself.isVariableNameInUse(pair[0])) {
                 myself.inform('that name is already in use');
             } else {
                 myself.addVariable(pair[0], pair[1]);
@@ -5269,6 +5407,13 @@ StageMorph.prototype.blockTemplates = function (category) {
         blocks.push(block('doHideVar'));
         blocks.push(block('doDeclareVariables'));
 
+    // inheritance:
+
+        blocks.push('-');
+        blocks.push(block('doDeleteAttr'));
+
+    ///////////////////////////////
+
         blocks.push('=');
 
         blocks.push(block('reportNewList'));
@@ -5660,6 +5805,14 @@ StageMorph.prototype.doubleDefinitionsFor
 StageMorph.prototype.replaceDoubleDefinitionsFor
     = SpriteMorph.prototype.replaceDoubleDefinitionsFor;
 
+// StageMorph inheritance support - variables
+
+StageMorph.prototype.isVariableNameInUse
+    = SpriteMorph.prototype.isVariableNameInUse;
+
+StageMorph.prototype.globalVariables
+    = SpriteMorph.prototype.globalVariables;
+
 // SpriteBubbleMorph ////////////////////////////////////////////////////////
 
 /*
@@ -6892,13 +7045,32 @@ WatcherMorph.prototype.setSliderMax = function (num) {
 // WatcherMorph updating:
 
 WatcherMorph.prototype.update = function () {
-    var newValue,
-        num;
+    var newValue, sprite, num;
+
     if (this.target && this.getter) {
         this.updateLabel();
         if (this.target instanceof VariableFrame) {
             newValue = this.target.vars[this.getter] ?
                     this.target.vars[this.getter].value : undefined;
+            if (newValue === undefined && this.target.owner) {
+                sprite = this.target.owner;
+                if (contains(sprite.inheritedVariableNames(), this.getter)) {
+                    newValue = this.target.getVar(this.getter);
+                    // ghost cell color
+                    this.cellMorph.setColor(
+                        SpriteMorph.prototype.blockColor.variables
+                            .lighter(35)
+                    );
+                } else {
+                    this.destroy();
+                    return;
+                }
+            } else {
+                // un-ghost the cell color
+                this.cellMorph.setColor(
+                    SpriteMorph.prototype.blockColor.variables
+                );
+            }
         } else {
             newValue = this.target[this.getter]();
         }
diff --git a/snap.html b/snap.html
index 976bcd6..234ed1f 100755
--- a/snap.html
+++ b/snap.html
@@ -2,7 +2,7 @@
 <html>
 	<head>
 		<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
-		<title>Snap! Build Your Own Blocks</title>
+		<title>Snap! Build Your Own Blocks. Development (OOP)</title>
 		<link rel="shortcut icon" href="favicon.ico">
 		<script type="text/javascript" src="morphic.js"></script>
 		<script type="text/javascript" src="widgets.js"></script>
diff --git a/store.js b/store.js
index d4a2b64..b2bb0a3 100644
--- a/store.js
+++ b/store.js
@@ -61,7 +61,7 @@ SyntaxElementMorph, Variable*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.store = '2015-March-15';
+modules.store = '2015-March-21';
 
 
 // XML_Serializer ///////////////////////////////////////////////////////
@@ -459,9 +459,17 @@ SnapSerializer.prototype.rawLoadProjectModel = function (xmlNode) {
         myself.loadValue(model);
     });
 
-    // restore nesting associations
+    // restore inheritance and nesting associations
     myself.project.stage.children.forEach(function (sprite) {
-        var anchor;
+        var exemplar, anchor;
+        if (sprite.inheritanceInfo) { // only sprites can inherit
+            exemplar = myself.project.sprites[
+                sprite.inheritanceInfo.exemplar
+            ];
+            if (exemplar) {
+                sprite.setExemplar(exemplar);
+            }
+        }
         if (sprite.nestingInfo) { // only sprites may have nesting info
             anchor = myself.project.sprites[sprite.nestingInfo.anchor];
             if (anchor) {
@@ -471,6 +479,7 @@ SnapSerializer.prototype.rawLoadProjectModel = function (xmlNode) {
         }
     });
     myself.project.stage.children.forEach(function (sprite) {
+        delete sprite.inheritanceInfo;
         if (sprite.nestingInfo) { // only sprites may have nesting info
             sprite.nestingScale = +(sprite.nestingInfo.scale || sprite.scale);
             delete sprite.nestingInfo;
@@ -639,9 +648,17 @@ SnapSerializer.prototype.loadSprites = function (xmlString, ide) {
         myself.loadObject(sprite, model);
     });
 
-    // restore nesting associations
+    // restore inheritance and nesting associations
     project.stage.children.forEach(function (sprite) {
-        var anchor;
+        var exemplar, anchor;
+        if (sprite.inheritanceInfo) { // only sprites can inherit
+            exemplar = project.sprites[
+                sprite.inheritanceInfo.exemplar
+            ];
+            if (exemplar) {
+                sprite.setExemplar(exemplar);
+            }
+        }
         if (sprite.nestingInfo) { // only sprites may have nesting info
             anchor = project.sprites[sprite.nestingInfo.anchor];
             if (anchor) {
@@ -651,6 +668,7 @@ SnapSerializer.prototype.loadSprites = function (xmlString, ide) {
         }
     });
     project.stage.children.forEach(function (sprite) {
+        delete sprite.inheritanceInfo;
         if (sprite.nestingInfo) { // only sprites may have nesting info
             sprite.nestingScale = +(sprite.nestingInfo.scale || sprite.scale);
             delete sprite.nestingInfo;
@@ -690,6 +708,7 @@ SnapSerializer.prototype.loadMediaModel = function (xmlNode) {
 SnapSerializer.prototype.loadObject = function (object, model) {
     // private
     var blocks = model.require('blocks');
+    this.loadInheritanceInfo(object, model);
     this.loadNestingInfo(object, model);
     this.loadCostumes(object, model);
     this.loadSounds(object, model);
@@ -699,6 +718,14 @@ SnapSerializer.prototype.loadObject = function (object, model) {
     this.loadScripts(object.scripts, model.require('scripts'));
 };
 
+SnapSerializer.prototype.loadInheritanceInfo = function (object, model) {
+    // private
+    var info = model.childNamed('inherit');
+    if (info) {
+        object.inheritanceInfo = info.attributes;
+    }
+};
+
 SnapSerializer.prototype.loadNestingInfo = function (object, model) {
     // private
     var info = model.childNamed('nest');
@@ -1467,6 +1494,7 @@ SpriteMorph.prototype.toXML = function (serializer) {
             ' draggable="@"' +
             '%' +
             ' costume="@" color="@,@,@" pen="@" ~>' +
+            '%' + // inheritance info
             '%' + // nesting info
             '<costumes>%</costumes>' +
             '<sounds>%</sounds>' +
@@ -1489,6 +1517,13 @@ SpriteMorph.prototype.toXML = function (serializer) {
         this.color.b,
         this.penPoint,
 
+        // inheritance info
+        this.exemplar
+            ? '<inherit exemplar="' +
+                    this.exemplar.name
+                    + '"/>'
+            : '',
+
         // nesting info
         this.anchor
             ? '<nest anchor="' +
diff --git a/threads.js b/threads.js
index 50af8dd..d3dcfc9 100644
--- a/threads.js
+++ b/threads.js
@@ -83,7 +83,7 @@ ArgLabelMorph, localize, XML_Element, hex_sha512*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.threads = '2015-February-28';
+modules.threads = '2015-March-21';
 
 var ThreadManager;
 var Process;
@@ -1159,7 +1159,7 @@ Process.prototype.doSetVar = function (varName, value) {
             name = name.expression.blockSpec;
         }
     }
-    varFrame.setVar(name, value);
+    varFrame.setVar(name, value, this.blockReceiver());
 };
 
 Process.prototype.doChangeVar = function (varName, value) {
@@ -1171,7 +1171,7 @@ Process.prototype.doChangeVar = function (varName, value) {
             name = name.expression.blockSpec;
         }
     }
-    varFrame.changeVar(name, value);
+    varFrame.changeVar(name, value, this.blockReceiver());
 };
 
 Process.prototype.reportGetVar = function () {
@@ -1295,6 +1295,20 @@ Process.prototype.doRemoveTemporaries = function () {
     }
 };
 
+// Process sprite inheritance primitives
+
+Process.prototype.doDeleteAttr = function (attrName) {
+    // currently only variables are deletable
+    var name = attrName;
+
+    if (name instanceof Context) {
+        if (name.expression.selector === 'reportGetVar') {
+            name = name.expression.blockSpec;
+        }
+    }
+    this.blockReceiver().deleteVariable(name);
+};
+
 // Process lists primitives
 
 Process.prototype.reportNewList = function (elements) {
@@ -3103,35 +3117,50 @@ VariableFrame.prototype.silentFind = function (name) {
     return null;
 };
 
-VariableFrame.prototype.setVar = function (name, value) {
-/*
-    change the specified variable if it exists
-    else throw an error, because variables need to be
-    declared explicitly (e.g. through a "script variables" block),
-    before they can be accessed.
-*/
+VariableFrame.prototype.setVar = function (name, value, sender) {
+    // change the specified variable if it exists
+    // else throw an error, because variables need to be
+    // declared explicitly (e.g. through a "script variables" block),
+    // before they can be accessed.
+    // if the found frame is inherited by the sender sprite
+    // shadow it (create an explicit one for the sender)
+    // before setting the value ("create-on-write")
+
     var frame = this.find(name);
     if (frame) {
-        frame.vars[name].value = value;
+        if (sender instanceof SpriteMorph &&
+                (frame.owner instanceof SpriteMorph) &&
+                (sender !== frame.owner)) {
+            sender.shadowVar(name, value);
+        } else {
+            frame.vars[name].value = value;
+        }
     }
 };
 
-VariableFrame.prototype.changeVar = function (name, delta) {
-/*
-    change the specified variable if it exists
-    else throw an error, because variables need to be
-    declared explicitly (e.g. through a "script variables" block,
-    before they can be accessed.
-*/
+VariableFrame.prototype.changeVar = function (name, delta, sender) {
+    // change the specified variable if it exists
+    // else throw an error, because variables need to be
+    // declared explicitly (e.g. through a "script variables" block,
+    // before they can be accessed.
+    // if the found frame is inherited by the sender sprite
+    // shadow it (create an explicit one for the sender)
+    // before changing the value ("create-on-write")
+
     var frame = this.find(name),
-        value;
+        value,
+        newValue;
     if (frame) {
         value = parseFloat(frame.vars[name].value);
-        if (isNaN(value)) {
-            frame.vars[name].value = delta;
+        newValue = isNaN(value) ? delta : value + parseFloat(delta);
+        if (sender instanceof SpriteMorph &&
+                (frame.owner instanceof SpriteMorph) &&
+                (sender !== frame.owner)) {
+            sender.shadowVar(name, newValue);
         } else {
-            frame.vars[name].value = value + parseFloat(delta);
+            frame.vars[name].value = newValue;
         }
+
     }
 };
 
diff --git a/widgets.js b/widgets.js
index bb250a8..b52782b 100644
--- a/widgets.js
+++ b/widgets.js
@@ -7,7 +7,7 @@
     written by Jens Mönig
     jens@moenig.org
 
-    Copyright (C) 2014 by Jens Mönig
+    Copyright (C) 2015 by Jens Mönig
 
     This file is part of Snap!.
 
@@ -74,7 +74,7 @@ HTMLCanvasElement, fontHeight, SymbolMorph, localize, SpeechBubbleMorph,
 ArrowMorph, MenuMorph, isString, isNil, SliderMorph, MorphicPreferences,
 ScrollFrameMorph*/
 
-modules.widgets = '2014-February-13';
+modules.widgets = '2015-March-21';
 
 var PushButtonMorph;
 var ToggleButtonMorph;
@@ -493,7 +493,7 @@ function ToggleButtonMorph(
     labelString,
     query, // predicate/selector
     environment,
-    hint,
+    hint, // optional, String or Function
     template, // optional, for cached background images
     minWidth, // <num> optional, if specified label will left-align
     hasPreview, // <bool> show press color on left edge (e.g. category)
@@ -560,12 +560,13 @@ ToggleButtonMorph.prototype.init = function (
 // ToggleButtonMorph events
 
 ToggleButtonMorph.prototype.mouseEnter = function () {
+    var contents = this.hint instanceof Function ? this.hint() : this.hint;
     if (!this.state) {
         this.image = this.highlightImage;
         this.changed();
     }
-    if (this.hint) {
-        this.bubbleHelp(this.hint);
+    if (contents) {
+        this.bubbleHelp(contents);
     }
 };