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, 7 insertions, 12 deletions

diff --git a/plugins/ltac/evar_tactics.ml b/plugins/ltac/evar_tactics.ml
index bf84f61a5..7db484d82 100644
--- a/plugins/ltac/evar_tactics.ml
+++ b/plugins/ltac/evar_tactics.ml
@@ -16,8 +16,6 @@ open Tacexpr
 open Refiner
 open Evd
 open Locus
-open Sigma.Notations
-open Proofview.Notations
 open Context.Named.Declaration
 
 module NamedDecl = Context.Named.Declaration
@@ -81,7 +79,7 @@ let instantiate_tac_by_name id c =
 
 let let_evar name typ =
   let src = (Loc.tag Evar_kinds.GoalEvar) in
-  Proofview.Goal.s_enter { s_enter = begin fun gl ->
+  Proofview.Goal.enter begin fun gl ->
     let sigma = Tacmach.New.project gl in
     let env = Proofview.Goal.env gl in
     let sigma = ref sigma in
@@ -93,17 +91,14 @@ let let_evar name typ =
       Namegen.next_ident_away_in_goal id (Termops.ids_of_named_context (Environ.named_context env))
     | Names.Name id -> id
     in
-    let sigma = Sigma.Unsafe.of_evar_map sigma in
-    let Sigma (evar, sigma, p) = Evarutil.new_evar env sigma ~src ~naming:(Misctypes.IntroFresh id) typ in
-    let tac =
-      (Tactics.letin_tac None (Names.Name id) evar None Locusops.nowhere)
-    in
-    Sigma (tac, sigma, p)
-  end }
+    let (sigma, evar) = Evarutil.new_evar env sigma ~src ~naming:(Misctypes.IntroFresh id) typ in
+    Tacticals.New.tclTHEN (Proofview.Unsafe.tclEVARS sigma)
+    (Tactics.letin_tac None (Names.Name id) evar None Locusops.nowhere)
+  end
 
 let hget_evar n =
   let open EConstr in
-  Proofview.Goal.nf_enter { enter = begin fun gl ->
+  Proofview.Goal.nf_enter begin fun gl ->
   let sigma = Tacmach.New.project gl in
   let concl = Proofview.Goal.concl gl in
   let evl = evar_list sigma concl in
@@ -113,5 +108,5 @@ let hget_evar n =
   let ev = List.nth evl (n-1) in
   let ev_type = EConstr.existential_type sigma ev in
   Tactics.change_concl (mkLetIn (Anonymous,mkEvar ev,ev_type,concl))
-  end }
+  end