Is there any way I could run functions in evaluate without using ()?

[JasXSL]

Background:
I made a poor decision many years ago when I started on a project, running a lot of math evaluations with a ton of variables using parser.set. Previously, it's worked fine to just calculate all variables before every evaluation and supplying them to parser.set. But now the variables I need and the time to calculate them has grown substantially. So I thought it'd be a better design to turn these variables into no-argument getter functions, so that they only need to be executed when they're actually used in an evaluation.

The problem:
Now I have formulas that might look like 3*dmg_taken, and if I want the dmg_taken variable to become a getter, I'd need to change my formula to 3*dmg_taken(). However, at this point there's thousands of formulas spread across the project, so going through and changing everything would take weeks.

Basically, is there a way I can call a function without requiring the parentheses if one is encountered, supplying no arguments?

[JasXSL]

I think I found it. Something like:

math.parse(formula).transform(node => {
  if( node.isSymbolNode && typeof myVars[node.name] === "function" )
    return new math.FunctionNode(node, []);
  return node;
}).evaluate(myVars);

[josdejong]

Instead of using Parser, you can use evaluate and pass a scope argument. This scope can be an Object or a Map interface.

A Map interface is any object having methods get, set, has, and keys, that allows you to evaluate variables lazily. Similarly, you can define getters on the object using Object.defineProperty or define property getters.

Here a very basic example:

// define a Map interface as scope
const scope = {
  has: (name) => name === 'dmg_taken' ? true : false,
  get: (name) => name === 'dmg_taken' ? 42 : undefined,
  keys: () => ['dmg_taken'],
  set: (name, value) => { /* TODO: implement */ }
}

math.evaluate('3*dmg_taken', scope) // 126