Listing undefined symbols of a MathNode

[zopieux]

Hi there,

I'm using mathjs to pre-compile (parse) a bunch of expressions. I'm left with a list of MathNodes. I need to get for each of them, post-simplify, what "free-standing" symbols it references aka depends on. The attempt helper below:

function symbols(node: MathNode): Set<string> {
  const symbols = new Set<string>()
  node.traverse((n) => (n.type == 'SymbolNode') && symbols.add(n.name))
  return symbols
}

gives both the free-standing symbols but also the builtin maths functions:

symbols(math.simplify('a+b+sqrt(b)+asin(c)'))
// a, b, sqrt, asin, c
// wanted instead: a, b, c

I could not find such an API in mathjs, does it exist? Here is equivalent nerdamer function that I need. Otherwise, as workaround, what would be a reliable way to exclude all builtins from the symbol list (ie. where are they stored please)?

Thanks!

[josdejong]

In the parsed expression there is indeed no difference between functions and symbols, nor between functions/symbols defined in mathjs or in your scope. Some tips:

• You can recognize function calls like sqrt and asin from symbols because they are defined as a FunctionNode having a property .fn being a SymbolNode with a .name property like sqrt or asin. You can use the third parent argument of node.traverse(function (node, path, parent) {...}) to check that.
• Whether something is a built-in function of mathjs can be verified by checking whether say math.asin and math.pi are defined.
• It is possible that a symbol is a unit like inch or millimeter, which will be resolved by mathjs when evaluating. To verify that, you can check the symbol against math.Unit.isValuelessUnit(name), which returns true for valid unit names.
• Not sure if relevant to you, but there are two static functions FunctionNode.onUndefinedFunction(name) and SymbolNode.onUndefinedSymbol(name) which can be overwritten to customize what to do when an undefined symbol is encountered whilst evaluating. I see these functions are not documented, I'll add them to the docs.

[zopieux]

Thanks for the reply and for improving the docs!