Higher-order function argument types

When I use a function as an argument, is there type information available that includes its domain and range?

It would be great to be able to do something like this:

function Nullable(f :: Function{X,Y}) 
    nx -> begin
        if isnull(nx)
            return Nullable{Y}()
            y = f(unsafe_get(x))
            return Nullable(y)

But the type information for functions in Julia is different than this, and doesn’t yet make sense to me. Is something like this possible, without hand-coding all of the types? Or does Julia even represent function types in a way I can extract this kind of information?


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It’s even more difficult than that. Functions in Julia don’t truly have arguments, only methods do. What you’re really looking for is a way to grab a method that has a specific signature, or ask if a function can have a given signature.

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