Now we follow Coq's stdlib and declare this instance using a `Hint Extern`;
this avoids making `flip` type class opaque.

Revert "`RelDecision` instance for `flip`, and make `flip` tc opaque to avoid loops due to eager unification."

This reverts commit b81aa3aa.

`RelDecision` instance for `flip`, and make `flip` tc opaque to avoid loops due to eager unification.

Otherwise type class search ocasionally unfolds them and finds
wrong instances. Based on an issue reported by @jihgfee.

This closes issue #25.

Jakob Botsch Nielsen authored 6 years ago and Robbert Krebbers committed 6 years ago

This changes the encoding used for finite lists of values of countable
types to be linear instead of exponential. The encoding works by
duplicating bits of each element so that 0 -> 00 and 1 -> 11, and then
separating each element with 10. The top 1-bits are not kept since we
know a 10 is starting a new element which ends with a 1.

Fix #28

Hopefully this fixes iris/iris#232

This fixes an issue in orc11.

- The class `Infinite A` is now defined as having a function
  `fresh : list A → A`, that given a list `xs`, gives an element `x ∉ xs`.
- For most types this `fresh` function has a sensible computable behavior,
  for example:
  + For numbers, it yields one added to the maximal element in `xs`.
  + For strings, it yields the first string representation of a number that is
    not in `xs`.
- For any type `C` of finite sets with elements of infinite type `A`, we lift
  the fresh function to `C → A`.

As a consequence:

- It is now possible to pick fresh elements from _any_ finite set and from
  _any_ list with elements of an infinite type. Before it was only possible
  for specific finite sets, e.g. `gset`, `pset`, ...
- It makes the code more uniform. There was a lot of overlap between having a
  `Fresh` and an `Infinite` instance. This got unified.