expr - tiny yet super fast math expression evaluator in Go

Example

vars := map[string]expr.Var{
	"x": NewVar(5),
}
funcs := map[string]expr.Func{
	"next": NewFunc(func(args expr.FuncArgs, env expr.FuncEnv) expr.Num {
		return expr.Num(args[0].Eval()+1)
	}),
}
vars["x"].Set(5)
e, err := expr.Parse("y=x+5/next(x)", vars, funcs)
if err != nil {
	log.Fatal(err)
}
result := e.Eval()
log.Println(result)
log.Println(vars["y"])

Performance

The goal is to speed up frequent evaluations of immutable expressions. For example, user enters a formula to calculate some metrics and backend does the calculation. Formula itself changes rarely, but is evaluated very often.

On my dual-core laptop the benchmark shows that:

• Parsing expression x=2+3*(x/(42+plusone(x))),x takes 14us, evaluation takes 65ns.
• Parsing a more complex expression of 280 chars takes 112us, evaluation takes 649ns.
• Parsing an even more complex expresison of ~3k chars takes 1ms, evaluation takes 7us.

This probably means that time grows linearly depending on the formula length and the performance is really good for short (human-generated) formulas.