ajm188 / go-ff Goto Github PK

https://github.com/slok/noglog

We should also update the README instructing people how to get noglog working, since replace directives don't apply transitively.

Things like:

• rand(n float64) float64
• ............. idk that's all i can come up with right now.

Abstractly I thought this was a good idea, but now that I'm playing around with this, anything that's idempotent can be precomputed and be provided via the parameters map in Evaluate, so there may not be a huge need for this.

There's also the whole thing where govaluate only actually deals in four types: float64, bool, string, and arrays, so the "correct" implementation a rand function is:

map[string]govaluate.ExpressionFunction{
	"rand": func(arguments ...interface{}) (interface{}, error) {
		if len(arguments) != 1 {
			return nil, fmt.Errorf("must provide one argument to rand, got %d", len(arguments))
		}

		n, ok := arguments[0].(float64)
		if !ok {
			return nil, fmt.Errorf("rand takes a numeric value, got %v (%T)", arguments[0], arguments[0])
		}

		return float64(rand.Intn(int(n))), nil
	}
}

If we don't explicitly cast the result of rand.Intn to a float64 then that value will be treated as a string in the expression, so an expression like rand(10) < 2 will fail because it's comparing a string and a float. So the whole thing also becomes kind of annoying to implement correctly.

An important note from the govaluate manual (emphasis mine):

During expression parsing (not evaluation), a map of functions can be given to govaluate.NewEvaluableExpressionWithFunctions (the lengthiest and finest of function names). The resultant expression will be able to invoke those functions during evaluation. Once parsed, an expression cannot have functions added or removed - a new expression will need to be created if you want to change the functions, or behavior of said functions.

So, managing that could get a bit tricky, depending on whether we want users to provide functions globally (pro: automatically available in every feature, don't have to remember which features have which functions available; con: have to re-parse every single feature anytime a function is added or removed, even if that feature doesn't use that function) or per-feature (same pro/con list but reversed). In any case, I wanted to get this written down before I inevitably forget.

Currently we use the default globalRand, and users can only control the behavior by calling rand.SetSeed, which applies globally and not just to the randomness used by feature.Get.

It might be nice to provide an API for setting a package-level source, or maybe that's a bad idea and using rand.SetSeed is Good Enough™