Types

Nilability = enum
  Parent, Safe, MaybeNil, Nil, Unreachable

Nilability : if a value is nilable. we have maybe nil and nil, so we can differentiate between cases where we know for sure a value is nil and not otherwise we can have Safe, MaybeNil Parent: is because we just use a sequence with the same length instead of a table, and we need to check if something was initialized at all: if Parent is set, then you need to check the parent nilability if the parent is nil, then for now we return MaybeNil unreachable is the result of add(Safe, Nil) and others it is a result of no states left, so it's usually e.g. in unreachable else branches?   Source   Edit

NilTransition = enum
  TArg, TAssign, TType, TNil, TVarArg, TResult, TSafe, TPotentialAlias,
  TDependant

transition kind: what was the reason for changing the nilability of

an expression useful for error messages and showing why an expression is being detected as nil / maybe nil

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