Hi Bart,
We just worked on something vaguely similar with @venkatd, for spreadsheet-like DAG computation definitions. We chose to eliminate the macro DSL we had prototyped because it went in the way of explicitness and prevented using function captures without adding a lot of workaround code. Some cells need to call the world, some cells need to be cached, some do not, and this is up to the user.
Now the API looks like :
defmodule MyDummySheet do
use ExSheet.FunctionDsl
def build_sheet() do
new()
|> input(:first_name, description: "A person's first name")
|> input(:last_name, description: "...")
|> input(:tenant_id)
|> input(:age)
|> cell(:full_name, inputs: [:first_name, :last_name], compute: fn (f, l) -> "#{f} #{l}" end, cache: true)
|> cell(:tenant_age_rule, inputs: [:tenant_id], compute: &MyApp.AgeRule.get_for_tenant/1)
|> cell(:passes_age_check, inputs: [:age, :tenant_age_rule], compute: fn age, rule -> rule.(age) end)
end
end
There is a bit more, but the core is a DAG of computation which you can selectively memoize or not. Usage of the given sheet is simple :
sheet = MyDummySheet.build_sheet
|> set(:first_name, "foo")
|> set(:first_name, "bar")
|> set(:tenant_id, 1)
|> set(:age, 21)
{passes, sheet} = get(sheet, :passes_age_check)
We use it for very different purposes. I use it to model UI state. We chose to keep the core API very small, but building on top of it is quite simple. For example, I’ve added a few helpers for sheet composition (nested computed state cleanly defined in separate modules) in my app that will not be in the core library.
The core of it is reactive calculations, but not linked to any framework or library. We have a few convenience helpers for collecting inputs to a map, and do not force a solution on how to hold a sheet in a process.
I see it as a way to organize an otherwise ad-hoc big “with” statement with laziness, dependency tracking, partial querying, and optional caching ?
My point is that maybe computed properties are interesting to be consumed by an UI layer or anything else, and might benefit of not being directly linked to Hologram ? Despite being super useful if you provide them.
