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, 4 insertions, 4 deletions

diff --git a/plugins/setoid_ring/newring.ml b/plugins/setoid_ring/newring.ml
index cca5cde15..85cbdc5a4 100644
--- a/plugins/setoid_ring/newring.ml
+++ b/plugins/setoid_ring/newring.ml
@@ -749,7 +749,7 @@ let ltac_ring_structure e =
    lemma1;lemma2;pretac;posttac]
 
 let ring_lookup (f : Value.t) lH rl t =
-  Proofview.Goal.enter { enter = begin fun gl ->
+  Proofview.Goal.enter begin fun gl ->
     let sigma = Tacmach.New.project gl in
     let env = Proofview.Goal.env gl in
     try (* find_ring_strucure can raise an exception *)
@@ -761,7 +761,7 @@ let ring_lookup (f : Value.t) lH rl t =
       let ring = ltac_ring_structure e in
       Proofview.tclTHEN (Proofview.Unsafe.tclEVARS !evdref) (ltac_apply f (ring@[lH;rl]))
     with e when Proofview.V82.catchable_exception e -> Proofview.tclZERO e
-  end }
+  end
 
 (***********************************************************************)
 
@@ -1035,7 +1035,7 @@ let ltac_field_structure e =
    field_simpl_eq_in_ok;cond_ok;pretac;posttac]
 
 let field_lookup (f : Value.t) lH rl t =
-  Proofview.Goal.enter { enter = begin fun gl ->
+  Proofview.Goal.enter begin fun gl ->
     let sigma = Tacmach.New.project gl in
     let env = Proofview.Goal.env gl in
     try
@@ -1047,4 +1047,4 @@ let field_lookup (f : Value.t) lH rl t =
       let field = ltac_field_structure e in
       Proofview.tclTHEN (Proofview.Unsafe.tclEVARS !evdref) (ltac_apply f (field@[lH;rl]))
     with e when Proofview.V82.catchable_exception e -> Proofview.tclZERO e
-  end }
+  end