Type_class: recursive instantiation

[cognivore]

Why does it have to be done?

For the following classes:

defclass A do
  def f(x), do: x
end

defclass B do
  def g(_x, y), do: y
end

defclass C do
  extend A
  extend B
  def h(x, _y), do: x
end

Being able to write the following instance:

definst C, for: X do
  def f(x), do: x.c
  def h(x, y), do: {x.c, y}
end

instead of

definst B, for: X
definst A, for: X do
  def f(x), do: x.value
end
definst C, for: X do
  def h(x, y), do: {x.value, y}
end

is actually a huge boost in ergonomics! Languages like Lean4 allow for it and it feels really good to be able to have the compiler resolve the typeclass dependencies and inject correct functions into correct places.

see here.

How do you think does it have to be done?

• Extract local functions with Macro.prewalk in definst
• Recursively build a list of "buckets" (the functions that are required to be provided by the classes a given class extends).
• Check which buckets are filled entirely by local functions.
• For each of such bucket, recursively call definst.
• If you have the time, optimise the amount of recursion in this implementation plan! If not, ship it :)

What do you think needs to be figured out for it to be done?

No response