`tc_to_bool` to turn a type class into a Boolean that expresses if there is an instance

This MR introduces the following function:

(** Given a proposition [P] that is a type class, [bool_of_tc P] will return
[true] iff there is an instance of [P]. *)
Definition bool_of_tc (P : Prop)
  {p : bool} `{TCIf P (TCEq p true) (TCEq p false)} : bool := p.

It's particularly useful in Ltac, where it's sometimes needed to figure out if an instance exists or not. An example use can be found in https://gitlab.mpi-sws.org/FP/iris-coq/merge_requests/199

I don't like these of function names. It's so backwards, putting the result before the argument. You clearly are too much influenced by how function signatures are written in C.^^

tc_to_bool is much better, IMO.

added 1 commit

• 512b3f99 - `tc_to_bool P` to turn a type class into a Boolean that represents if there is an instance.

Compare with previous version

Agreed, also most of the other TC related functions in that file are called tc_.

changed title from {-bool_of_tc to turn a type class into a Boolean that represent-}s if there is an instance to {+tc_to_bool to turn a type class into a Boolean that expresse+}s if there is an instance

changed the description

Going to merge.

mentioned in commit 48758ab8

merged

mentioned in merge request !45 (merged)