new "combine" primitive in list category

HISTORY.md

@@ -25,7 +25,7 @@
     * new "get graphic effect" reporter
     * new "get pen attribute" reporter
     * new "write" command in pen category (used to be "label" in tools)
-    * new "map","keep" and "for each" primitives in list category
+    * new "map","keep", "combine" and "for each" primitives in list category
     * added "neg", "lg" (log2) and "2^" selectors to monadic function reporter in Operators
     * added "^" reporter (power of) in the Operators category
     * added "width" and "height" as attribute selectors of the OF primitive for the stage
@@ -68,6 +68,9 @@
     * German
     * French
 
+### 2019-04-24
+* Threads: new "combine" primitive in list category
+
 ### 2019-04-23
 * Threads: fixed JS stack overflow issue for MAP primitive
 * Threads: new "map" and "for each" primitives in list category

snap.html

@@ -7,8 +7,8 @@
         <script type="text/javascript" src="src/morphic.js?version=2019-02-07"></script>
         <script type="text/javascript" src="src/widgets.js?version=2019-04-05"></script>
         <script type="text/javascript" src="src/blocks.js?version=2019-04-11"></script>
-        <script type="text/javascript" src="src/threads.js?version=2019-04-23"></script>
-        <script type="text/javascript" src="src/objects.js?version=2019-04-23"></script>
+        <script type="text/javascript" src="src/threads.js?version=2019-04-24"></script>
+        <script type="text/javascript" src="src/objects.js?version=2019-04-24"></script>
         <script type="text/javascript" src="src/gui.js?version=2019-04-10"></script>
         <script type="text/javascript" src="src/paint.js?version=2019-02-22"></script>
         <script type="text/javascript" src="src/lists.js?version=2019-02-07"></script>

src/objects.js

@@ -84,7 +84,7 @@ BlockEditorMorph, BlockDialogMorph, PrototypeHatBlockMorph, localize,
 TableMorph, TableFrameMorph, normalizeCanvas, BooleanSlotMorph, HandleMorph,
 AlignmentMorph, Process, XML_Element, VectorPaintEditorMorph*/
 
-modules.objects = '2019-April-23';
+modules.objects = '2019-April-24';
 
 var SpriteMorph;
 var StageMorph;
@@ -1270,6 +1270,16 @@ SpriteMorph.prototype.initBlocks = function () {
             category: 'lists',
             spec: 'map %repRing over %l'
         },
+        reportKeep: {
+            type: 'reporter',
+            category: 'lists',
+            spec: 'keep items such that %predRing from %l'
+        },
+        reportCombine: {
+            type: 'reporter',
+            category: 'lists',
+            spec: 'combine with %repRing items of %l'
+        },
         doForEach: {
             type: 'command',
             category: 'lists',
@@ -2401,6 +2411,7 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         blocks.push('=');
 
         blocks.push(block('reportNewList'));
+        blocks.push('-');
         blocks.push(block('reportCONS'));
         blocks.push(block('reportListItem'));
         blocks.push(block('reportCDR'));
@@ -2410,6 +2421,8 @@ SpriteMorph.prototype.blockTemplates = function (category) {
         blocks.push('-');
         blocks.push(block('doForEach'));
         blocks.push(block('reportMap'));
+        blocks.push(block('reportKeep'));
+        blocks.push(block('reportCombine'));
         blocks.push('-');
         blocks.push(block('doAddToList'));
         blocks.push(block('doDeleteFromList'));
@@ -2591,6 +2604,8 @@ SpriteMorph.prototype.freshPalette = function (category) {
                         'reportListContainsItem',
                         'doForEach',
                         'reportMap',
+                        'reportKeep',
+                        'reportCombine',
                         'doAddToList',
                         'doDeleteFromList',
                         'doInsertInList',
@@ -7947,6 +7962,7 @@ StageMorph.prototype.blockTemplates = function (category) {
         blocks.push(block('doDeclareVariables'));
         blocks.push('=');
         blocks.push(block('reportNewList'));
+        blocks.push('-');
         blocks.push(block('reportCONS'));
         blocks.push(block('reportListItem'));
         blocks.push(block('reportCDR'));
@@ -7956,6 +7972,8 @@ StageMorph.prototype.blockTemplates = function (category) {
         blocks.push('-');
         blocks.push(block('doForEach'));
         blocks.push(block('reportMap'));
+        blocks.push(block('reportKeep'));
+        blocks.push(block('reportCombine'));
         blocks.push('-');
         blocks.push(block('doAddToList'));
         blocks.push(block('doDeleteFromList'));

src/threads.js

@@ -62,7 +62,7 @@ StageMorph, SpriteMorph, StagePrompterMorph, Note, modules, isString, copy,
 isNil, WatcherMorph, List, ListWatcherMorph, alert, console, TableMorph, Color,
 TableFrameMorph, ColorSlotMorph, isSnapObject, Map, newCanvas, Symbol*/
 
-modules.threads = '2019-April-23';
+modules.threads = '2019-April-24';
 
 var ThreadManager;
 var Process;
@@ -2192,6 +2192,60 @@ Process.prototype.reportKeep = function (predicate, list) {
     this.evaluate(predicate, new List([next]));
 };
 
+Process.prototype.reportCombine = function (reporter, list) {
+    // Fold - answer an aggregation of all list items from "left to right"
+    // Distinguish between linked and arrayed lists.
+
+    // this.context.inputs:
+    // [0] - predicate
+    // [1] - list (original source)
+    // -----------------------------
+    // [2] - last predicate evaluation result
+
+    var next, current;
+    if (list.length() < 2) {
+        this.returnValueToParentContext(list.length() ? list.at(1) : 0);
+        return;
+    }
+    if (list.isLinked) {
+        if (this.context.aggregation === null) {
+            this.context.aggregation = {
+                source : list.cdr(),
+                target : list.at(1),
+                remaining : list.length() - 1
+            };
+        } else if (this.context.inputs.length > 2) {
+            this.context.aggregation.target = this.context.inputs.pop();
+            this.context.aggregation.remaining -= 1;
+            this.context.aggregation.source =
+                this.context.aggregation.source.cdr();
+        }
+        if (this.context.aggregation.remaining === 0) {
+            this.returnValueToParentContext(this.context.aggregation.target);
+            return;
+        }
+        next = this.context.aggregation.source.at(1);
+    } else { // arrayed
+        if (this.context.aggregation === null) {
+            this.context.aggregation = {
+                idx : 1,
+                target : list.at(1)
+            };
+        } else if (this.context.inputs.length > 2) {
+            this.context.aggregation.target = this.context.inputs.pop();
+        }
+        if (this.context.aggregation.idx === list.length()) {
+            this.returnValueToParentContext(this.context.aggregation.target);
+            return;
+        }
+        this.context.aggregation.idx += 1;
+        next = list.at(this.context.aggregation.idx);
+    }
+    current = this.context.aggregation.target;
+    this.pushContext();
+    this.evaluate(reporter, new List([current, next]));
+};
+
 Process.prototype.doForEach = function (upvar, list, script) {
     // perform a script for each element of a list, assigning the
     // current iteration's element to a variable with the name