PEG.js arithmetics

xholonWorkbook.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--Xholon Workbook http://www.primordion.com/Xholon/gwt/ MIT License, Copyright (C) Ken Webb, Wed Jun 21 2017 12:05:38 GMT-0400 (EDT)-->
<XholonWorkbook>

<Notes><![CDATA[
Xholon
------
Title: PEG.js arithmetics
Description: 
Url: http://www.primordion.com/Xholon/gwt/
InternalName: 7746de2abd4576de67e9a76eebc5fe6b
Keywords: 

My Notes
--------
June 21, 2017
Investigate the use of PEG.js to generate parsers.

To install PEG.js (from a terminal)
-----------------
sudo npm install -g pegjs

To test it (from a terminal)
----------
pegjs -h
pegjs --format globals --export-var PEG arithmetics.pegjs
  - this generates arithmetics.js

arithmetics.pegjs
-----------------
// Simple Arithmetics Grammar
// ==========================
//
// Accepts expressions like "2 * (3 + 4)" and computes their value.

Expression
  = head:Term tail:(_ ("+" / "-") _ Term)* {
      return tail.reduce(function(result, element) {
        if (element[1] === "+") { return result + element[3]; }
        if (element[1] === "-") { return result - element[3]; }
      }, head);
    }

Term
  = head:Factor tail:(_ ("*" / "/") _ Factor)* {
      return tail.reduce(function(result, element) {
        if (element[1] === "*") { return result * element[3]; }
        if (element[1] === "/") { return result / element[3]; }
      }, head);
    }

Factor
  = "(" _ expr:Expression _ ")" { return expr; }
  / Integer

Integer "integer"
  = _ [0-9]+ { return parseInt(text(), 10); }

_ "whitespace"
  = [ \t\n\r]*


References
----------
(1) https://github.com/pegjs/pegjs
(2) http://pegjs.org/

]]></Notes> 

<_-.XholonClass>
  <PhysicalSystem/>
  
  <RoundPeg/>
  
</_-.XholonClass>

<xholonClassDetails>
  
</xholonClassDetails>

<PhysicalSystem>
  <RoundPeg/>
</PhysicalSystem>

<RoundPegbehavior implName="org.primordion.xholon.base.Behavior_gwtjs"><![CDATA[
var me, beh = {
postConfigure: function() {
  me = this.cnode.parent();
  $wnd.xh.param("TimeStepInterval","1000");
  $wnd.xh.require("pegjs/arithmetics");
},
act: function() {
  if ($wnd.PEG) {
    me.println($wnd.PEG.parse("5 + 7")); // 12
    me.println($wnd.PEG.parse("(5 + 7) - 3")); // 9
  }
}
}
]]></RoundPegbehavior>

<SvgClient><Attribute_String roleName="svgUri"><![CDATA[data:image/svg+xml,
<svg width="100" height="50" xmlns="http://www.w3.org/2000/svg">
  <g>
    <title>Round Peg</title>
    <rect id="PhysicalSystem/RoundPeg" fill="#98FB98" height="50" width="50" x="25" y="0"/>
    <g>
      <title>Round Peg again</title>
      <rect id="PhysicalSystem/RoundPeg" 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>