Thanks for the responses.
Ultimately what I'd like is a 'curve-by-equation' to be available in a sketch, whereby the user can define multiple functions which are evaluated over the domain of a parameter to define a curve. This could end up being quite complex - my use for it previously required solving fourth-order polynomials - so definitely more than a single y = f(x) scenario.
I've recently (for work, for a different purpose) been using an expression parser in C# which is what's prompted me to start thinking about it here. Right now I'm just looking at different possibilities for the parser and it will be a while before I think about anything integrating with FreeCAD (at which point I'll have a massive learning curve figuring how and where to fit it in), but I wanted to be sure that I didn't get too far with a library that couldn't be used.
I agree that linking as an external library would be preferable, but I'm not sure these are available as libraries 'off-the-shelf' as it were. I've been looking at the options here https://github.com/ArashPartow/math-par ... rk-project
, primarily ExprTk (which looks powerful and useful but weighty) or TinyExpr, and I'm not sure these come ready packaged (and look like being only a file or two). I suppose I could still compile it into it's own library? Maybe someone knows of something already packaged that I should consider?
I hope nothing above sounds unreasonable, I'm keen to get back into FreeCAD and it's easier when driven by a mini-project of my own.