Expression Machine

Library for evaluating logic expressions at runtime.

Features

• Basic arithmetic operations (addition, subtraction, multiplication, division)
• Parentheses for grouping operations
• Injectable float variables
• Injectable functions accepting one or no input arguments

Example

Below is an example that fills a destination span with coordinates for the points of a circle, with either a radius or a diameter as input. While reusing the same machine instance by modifying its source and variables, and re-evaluating the expression.

public void GetCirclePositions(float radius, Span<Vector2> positions)
{
    using Machine vm = new();
    vm.SetVariable("value", value);
    vm.SetFunction("cos", MathF.Cos);
    vm.SetFunction("sin", MathF.Sin);

    int length = positions.Length;
    for (int i = 0; i < length; i++)
    {
        float t = i * MathF.PI / (length * 0.5f);
        vm.SetVariable("t", t);
        vm.SetSource("cos(t) * radius");
        float x = vm.Evaluate();    
        vm.SetSource("sin(t) * radius");
        float y = vm.Evaluate();
        positions[i] = new Vector2(x, y);
    }
}

Checking for compilation issues

When a text source is assigned to the machine, it returns a compilation result. This result value can be used to check if there were issues. And can do so with the try-do pattern:

if (vm.TrySetSource("5 +", out Exception? exception))
{
    //success
}
else
{
    //error
    throw exception;
}

Contributions and direction

This library is small and isn't mean to substitute things like Lua or other languages within interpreters. Instead, it's more fitting as a base to extend upon and branch away. And it should remain as unmanaged as it is. Without extending it, it's most useful fruit is allowing your code to express different values, all through a single C# variable via different expressions.

Contributions that align with this are welcome.