Remove the Sigma (monotonous state) API.

Reminder of (some of) the reasons for removal:

- Despite the claim in sigma.mli, it does *not* prevent evar
  leaks, something like:

  fun env evd ->
  let (evd',ev) = new_evar env evd in
  (evd,ev)

  will typecheck even with Sigma-like type annotations (with a proof of
  reflexivity)

- The API stayed embryonic. Even typing functions were not ported to
  Sigma.

- Some unsafe combinators (Unsafe.tclEVARS) were replaced with slightly
  less unsafe ones (e.g. s_enter), but those ones were not marked unsafe
  at all (despite still being so).

- There was no good story for higher order functions manipulating evar
  maps. Without higher order, one can most of the time get away with
  reusing the same name for the updated evar map.

- Most of the code doing complex things with evar maps was using unsafe
  casts to sigma. This code should be fixed, but this is an orthogonal
  issue.

Of course, this was showing a nice and elegant use of GADTs, but the
cost/benefit ratio in practice did not seem good.

1 files changed, 2 insertions, 11 deletions

diff --git a/engine/ftactic.mli b/engine/ftactic.mli
index 5db373199..97bebe9da 100644
--- a/engine/ftactic.mli
+++ b/engine/ftactic.mli
@@ -6,8 +6,6 @@
 (*         *       GNU Lesser General Public License Version 2.1        *)
 (************************************************************************)
 
-open Proofview.Notations
-
 (** This module defines potentially focussing tactics. They are used by Ltac to
     emulate the historical behaviour of always-focussed tactics while still
     allowing to remain global when the goal is not needed. *)
@@ -41,20 +39,13 @@ val run : 'a t -> ('a -> unit Proofview.tactic) -> unit Proofview.tactic
 
 (** {5 Focussing} *)
 
-val nf_enter : ([ `NF ], 'a t) enter -> 'a t
+val nf_enter : ([ `NF ] Proofview.Goal.t -> 'a t) -> 'a t
 (** Enter a goal. The resulting tactic is focussed. *)
 
-val enter : ([ `LZ ], 'a t) enter -> 'a t
+val enter : ([ `LZ ] Proofview.Goal.t -> 'a t) -> 'a t
 (** Enter a goal, without evar normalization. The resulting tactic is
     focussed. *)
 
-val s_enter : ([ `LZ ], 'a t) s_enter -> 'a t
-(** Enter a goal and put back an evarmap. The resulting tactic is focussed. *)
-
-val nf_s_enter : ([ `NF ], 'a t) s_enter -> 'a t
-(** Enter a goal, without evar normalization and put back an evarmap. The
-    resulting tactic is focussed. *)
-
 val with_env : 'a t -> (Environ.env*'a) t
 (** [with_env t] returns, in addition to the return type of [t], an
     environment, which is the global environment if [t] does not focus on