IsFunc()-like test: IsCallable()? Topic is solved

[sirksel]

Now that we have closures/lambdas (thanks again, Lexikos!), I find myself using type(obj)=='Func' or type(obj)=='Closure' a lot to test whether or not a parameter is callable with .Call(). I use this primarily when a function can take a parameter that can be either a value or a function/lambda returning a value based on other variables. Defining IsCallable(obj) in my library was trivial: (EDIT: code edited to reflect subsequent comments)

Code: Select all

IsCallable(obj) {  ; if callable, returns truthy minimum params + 1 (returns -1 for BoundFunc), else 0/false
  return (t:=type(obj))=='Closure' or t=='Func' ? obj.minparams+1 : t=='BoundFunc' ? -1 : 0
}

However, I wondered if maybe I missed a more obvious way to do this with an existing (or recently added) function? If not, since Func and Closure objects (while rightfully distinct objects/concepts) share the same properties/methods, would it make sense to have a built-in test like this that guarantees these parallel properties/methods work?

[nnnik]

But you havent got bound funcs covered

[sirksel]

Great point, nnnik! No sooner did I edit/repost my code than I discovered that simply adding or t=='BoundFunc' invalidates the truthiness/minparams branch of the return, since BoundFunc doesn't support any methods other than .Call. (I think that's why I initially excluded it, now that I think about it.) It would definitely be better if BoundFunc supported .minparams, but no big deal. I do think some union test like this might make a good built-in candidate, but it would be justifiably low on the priority list. Anyone who wants it can build it.

[nnnik]

Well and now there are still objects that implement .call().

[nnnik]

And Im not sure that closures implement minParams and maxParams either.

[Helgef]

Closures have the same properties and methods as func objects.

[lexikos]

Returning MinParams makes it impossible to distinguish between something which isn't callable and a function with no mandatory parameters. This is why IsFunc returns 1 + MinParams. For "is callable", it would make more sense to provide optional parameters to enable further verification; i.e. "is callable with x params". Of course, that verification may be impossible in some cases.

I have tentative plans to enable detection of methods and/or retrieving references to built-in methods. In either case, "is callable" can be inferred by "has a call method".