Add e.eq(a, b, exact: bool)

[PgBiel]

Recursively check for equality, avoiding pitfalls where eid(a) == eid(b) but func(a) != func(b) for elements (and similarly for custom types with tid(a) == tid(b))

With the exact parameter, we can also check for strict equality, which would allow us to properly implement dictionary and array literals (right now exact(...) on them doesn't work as expected).

Some ideas:

• exact: false impl:

  • If a == b works, return true
  • If both are custom types with the same tid, then apply eq(a.field, b.field, exact: exact) for each field recursively
  • If both are custom elements with the same eid, then apply eq(a.field, b.field, exact: exact) for each field recursively
  • If both are dictionaries, apply eq(a.at(k), b.at(k), exact: exact) recursively (fail early if there is k in a which is not in b or vice-versa)
  • If both are arrays (fail early if they have different lengths), apply eq(a.at(i), b.at(i), exact: exact) recursively
  • Otherwise false
  • Possible optimization: Elements and types store whether all of their fields are "simple" to compare (fields(a) == fields(b) is enough), e.g. not structured (not content, dict or array)

• exact: true impl:

  • If type(a) != type(b) return false early
  • If a == b and a, b are both "simple" types (not dictionary / array / content), then return true
  • Otherwise do the rest of the procedure above