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, 5 insertions, 6 deletions

diff --git a/plugins/firstorder/g_ground.ml4 b/plugins/firstorder/g_ground.ml4
index bbb9feae2..e3fab6d01 100644
--- a/plugins/firstorder/g_ground.ml4
+++ b/plugins/firstorder/g_ground.ml4
@@ -15,7 +15,6 @@ open Ground
 open Goptions
 open Tacmach.New
 open Tacticals.New
-open Proofview.Notations
 open Tacinterp
 open Libnames
 open Stdarg
@@ -84,24 +83,24 @@ let fail_solver=tclFAIL 0 (Pp.str "GTauto failed")
 let gen_ground_tac flag taco ids bases =
   let backup= !qflag in
   Proofview.tclOR begin
-  Proofview.Goal.enter { enter = begin fun gl ->
+  Proofview.Goal.enter begin fun gl ->
       qflag:=flag;
       let solver=
 	match taco with
 	    Some tac-> tac
 	  | None-> snd (default_solver ()) in
       let startseq k =
-        Proofview.Goal.s_enter { s_enter = begin fun gl ->
+        Proofview.Goal.enter begin fun gl ->
 	let seq=empty_seq !ground_depth in
         let seq, sigma = extend_with_ref_list (pf_env gl) (project gl) ids seq in
         let seq, sigma = extend_with_auto_hints (pf_env gl) (project gl) bases seq in
-        Sigma.Unsafe.of_pair (k seq, sigma)
-        end }
+        tclTHEN (Proofview.Unsafe.tclEVARS sigma) (k seq)
+        end
       in
       let result=ground_tac solver startseq in
       qflag := backup;
       result
-  end }
+  end
   end
   (fun (e, info) -> qflag := backup; Proofview.tclZERO ~info e)