Why is reduce with concatenation type unstable?

[yuyichao]

@jishnub

I find this surprising as vcat does not behave like this:

But reduce is not splatting. What you are doing is equivalent to

1, vcat(1, 2), vcat(vcat(1, 2), 3) etc…

@jishnub

Why is the type-unstable definition the default?

And this has nothing to do with type stability. It’s just how it must behave by the definition.