Simplicity copy-on-write

xholonWorkbook.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--Xholon Workbook http://www.primordion.com/Xholon/gwt/ MIT License, Copyright (C) Ken Webb, Mon Dec 15 2025 12:40:08 GMT-0500 (Eastern Standard Time)-->
<XholonWorkbook>

<Notes><![CDATA[
Xholon
------
Title: Simplicity copy-on-write
Description: 
Url: http://www.primordion.com/Xholon/gwt/
InternalName: 4e8563ff391e77e2029c8da3450e2d37
Keywords: 

My Notes
--------
2025 Dec 15

Experiment with concepts in ref[1], especially copy-on-write (COW) in chapter 6.

### References
(1) Eric Normand, grokking Simplicity, 2021 - chapter 6
    chapter 6 - Staying immutable in a mutable labguage
    shopping cart operations using a copy-on-write discipline
    three steps:
    1. Make a copy
    2. Modify the copy (as much as you want)
    3. Return the copy

() 

]]></Notes>  

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  <Cow superClass="Script"/>
  
</_-.XholonClass>

<xholonClassDetails>
  
  <Cow><Color>orange</Color></Cow>
  <Avatar><Color>red</Color></Avatar>
  
</xholonClassDetails>

<PhysicalSystem>
  
  <Cow roleName="aldebaran"><![CDATA[
var me, shoppingCart, count, beh = {
  postConfigure: function() {
    me = this.cnode;
    shoppingCart = [
      {name: "bread", price: 12.34},
      {name: "broccoli", price: 5.66}
    ];
    count = 0;
  },
  act: function() {
    me.println(me.name() + " " + JSON.stringify(shoppingCart));
    switch (count) {
    case 0:
      shoppingCart = this.remove_item_by_name(shoppingCart, "broccoli");
      shoppingCart = this.add_item(shoppingCart, {name: "bananas", price: 0.33});
      break;
    case 1:
      shoppingCart = this.remove_item_by_name(shoppingCart, "bread");
      break;
    default: break;
    }
    count++;
  },
  remove_item_by_name: function(cart, name) {
    // this is how the function is coded on p. 117 of the book
    var new_cart = cart.slice();
    var idx = null;
    for (var i = 0; i < new_cart.length; i++) {
      if (new_cart[i].name === name)
        idx = i;
    }
    if (idx !== null) 
      new_cart.splice(idx, 1);
    return new_cart;
  },
  add_item: function(cart, item) {
    // this is my function
    var new_cart = cart.slice();
    new_cart.push(item);
    return new_cart;
  }
}
//# sourceURL=aldebaran.js  
  ]]></Cow>
  
  <Cow roleName="betelgeuse"><![CDATA[
var me, shoppingCart, beh = {
  postConfigure: function() {
    me = this.cnode;
    shoppingCart = [
      {name: "tomatoes", price: 12.02},
      {name: "potatoes", price: 5.01}
    ];
  },
  act: function() {
    me.println(me.name() + " " + JSON.stringify(shoppingCart));
  }
}
//# sourceURL=betelgeuse.js  
  ]]></Cow>
  
</PhysicalSystem>

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<svg width="100" height="50" xmlns="http://www.w3.org/2000/svg">
  <g>
    <title>Cow</title>
    <rect id="PhysicalSystem/Cow" fill="#98FB98" height="50" width="50" x="25" y="0"/>
    <g>
      <title>Cow</title>
      <rect id="PhysicalSystem/Cow" fill="#6AB06A" height="50" width="10" x="80" y="0"/>
    </g>
  </g>
</svg>
]]></Attribute_String><Attribute_String roleName="setup">${MODELNAME_DEFAULT},${SVGURI_DEFAULT}</Attribute_String></SvgClient>

</XholonWorkbook>