How do you define a function?

[leshow]

I'm trying to figure out how to define a function inside VRL. I assumed because you can pass a function with |foo| {} that this would work on assignment as well, but it doesn't appear to be valid. I haven't been able to find it in the docs, what am I missing?
looking for something like

my_fn = |val| {
...
}

so that I can call it later with my_fn(foo)

[jszwedko]

Unfortunately this isn't possible yet, see #47