CLEANUP: Context.{Rel,Named}.Declaration.t

  Originally, rel-context was represented as:

    Context.rel_context = Names.Name.t * Constr.t option * Constr.t

  Now it is represented as:

    Context.Rel.t = LocalAssum of Names.Name.t * Constr.t
                  | LocalDef of Names.Name.t * Constr.t * Constr.t

  Originally, named-context was represented as:

    Context.named_context = Names.Id.t * Constr.t option * Constr.t

  Now it is represented as:

    Context.Named.t = LocalAssum of Names.Id.t * Constr.t
                    | LocalDef of Names.Id.t * Constr.t * Constr.t

Motivation:

  (1) In "tactics/hipattern.ml4" file we define "test_strict_disjunction"
      function which looked like this:

        let test_strict_disjunction n lc =
          Array.for_all_i (fun i c ->
            match (prod_assum (snd (decompose_prod_n_assum n c))) with
            | [_,None,c] -> isRel c && Int.equal (destRel c) (n - i)
            | _ -> false) 0 lc

      Suppose that you do not know about rel-context and named-context.
      (that is the case of people who just started to read the source code)
      Merlin would tell you that the type of the value you are destructing
      by "match" is:

        'a * 'b option * Constr.t                    (* worst-case scenario *)

      or

        Named.Name.t * Constr.t option * Constr.t    (* best-case scenario (?) *)

      To me, this is akin to wearing an opaque veil.
      It is hard to figure out the meaning of the values you are looking at.
      In particular, it is hard to discover the connection between the value
      we are destructing above and the datatypes and functions defined
      in the "kernel/context.ml" file.

      In this case, the connection is there, but it is not visible
      (between the function above and the "Context" module).

      ------------------------------------------------------------------------

      Now consider, what happens when the reader see the same function
      presented in the following form:

        let test_strict_disjunction n lc =
          Array.for_all_i (fun i c ->
            match (prod_assum (snd (decompose_prod_n_assum n c))) with
            | [LocalAssum (_,c)] -> isRel c && Int.equal (destRel c) (n - i)
            | _ -> false) 0 lc

      If the reader haven't seen "LocalAssum" before, (s)he can use Merlin
      to jump to the corresponding definition and learn more.

      In this case, the connection is there, and it is directly visible
      (between the function above and the "Context" module).

  (2) Also, if we already have the concepts such as:
      - local declaration
      - local assumption
      - local definition
      and we describe these notions meticulously in the Reference Manual,
      then it is a real pity not to reinforce the connection
      of the actual code with the abstract description we published.

1 files changed, 9 insertions, 8 deletions

diff --git a/kernel/nativecode.ml b/kernel/nativecode.ml
index 711096b2b..47274a5cd 100644
--- a/kernel/nativecode.ml
+++ b/kernel/nativecode.ml
@@ -1832,24 +1832,25 @@ and apply_fv env sigma univ (fv_named,fv_rel) auxdefs ml =
   auxdefs, MLlet(aux_name, ml, mkMLapp (MLlocal aux_name) (Array.of_list (fv_rel@fv_named)))
 
 and compile_rel env sigma univ auxdefs n =
-  let (_,body,_) = Context.Rel.lookup n env.env_rel_context in
+  let decl = Context.Rel.lookup n env.env_rel_context in
   let n = Context.Rel.length env.env_rel_context - n in
-  match body with
-  | Some t ->
+  let open Context.Rel.Declaration in
+  match decl with
+  | LocalDef (_,t,_) ->
       let code = lambda_of_constr env sigma t in
       let auxdefs,code = compile_with_fv env sigma univ auxdefs None code in
       Glet(Grel n, code)::auxdefs
-  | None -> 
+  | LocalAssum _ ->
       Glet(Grel n, MLprimitive (Mk_rel n))::auxdefs
 
 and compile_named env sigma univ auxdefs id =
-  let (_,body,_) = Context.Named.lookup id env.env_named_context in
-  match body with
-  | Some t ->
+  let open Context.Named.Declaration in
+  match Context.Named.lookup id env.env_named_context with
+  | LocalDef (_,t,_) ->
       let code = lambda_of_constr env sigma t in
       let auxdefs,code = compile_with_fv env sigma univ auxdefs None code in
       Glet(Gnamed id, code)::auxdefs
-  | None -> 
+  | LocalAssum _ ->
       Glet(Gnamed id, MLprimitive (Mk_var id))::auxdefs
 
 let compile_constant env sigma prefix ~interactive con cb =