Partial trait

[lukaszcz]

Once we have traits, we could create a Partial typeclass like in PureScript:

https://book.purescript.org/chapter6.html#nullary-type-classes

This would allow to use partial functions in an encapsulated manner and without depending on the Debug module. Currently, e.g., the head function depends on Debug.fail.

We could rename Debug.fail to Debug.abort.

Add a trait:

trait
type Partial := mkPartial {
   fail : {A : Type} -> A
};

runPartial {A} (f : {{Partial}} -> A) : A := f {{mkPartial __builtin_fail}};