Add sneaky invoke example (from Slack)

[phipsgabler]

I cleaned it up a bit as well.

[MikeInnes]

Is it necessary to split this out? I can see this being useful for development but for show it off we should probably make it as simple as possible.

[phipsgabler]

Not at all. But accessing parameters[1] just felt kind of ugly to me. OTOH, for a show off, it shows the semantics much more clearly: that we need to get rid of a level of Type here.

[MikeInnes]

For that you need concrete but I don't see that it needs _sneaky_transform to be split out, because that's not doing any unwrapping, it just passes through arguments without modification.

It could work well to just do @dynamo function sneakyinvoke(f, Type{T}, ...) where T<:Tuple. The dynamo type signature refers to the unwrapped parameters so that might be a cleaner way to unwrap that avoids the utility functions.

[MikeInnes]

I was wrong above due to #41, but I've pushed a fix which makes the following work:

@dynamo function sneakyinvoke(f, ::Type{T}, args...) where T<:Tuple
    ir = IR(f, T.parameters...)
    argument!(ir, at = 2)
    return ir
end

I think this is a slightly more idiomatic way to do the unwrapping.

[MasonProtter]

I would also give this example:

println("Get around overly restrictive type annotations")
@show sneakyinvoke((x::Float64) -> x + 1, Tuple{Float64}, 1)

[MikeInnes]

Hope you don't mind that I made those small tweaks. Thanks a lot for working out this example!

[phipsgabler]

Sure I don't mind. And about #41: of course that's exactly why I wrote it that way :) In fact, I have just always accepted this limitation and never considered it a missing feature.