This commit introduces changes in induction and destruct.

The main change is that selection of subterm is made similar whether
the given term is fully applied or not.
- The selection of subterm now works as follows depending on whether
  the "at" is given, of whether the subterm is fully applied or not,
  and whether there are incompatible subterms matching the pattern. In
  particular, we have:
  "at" given
  | subterm fully applied
  | | incompatible subterms
  | | |
  Y Y - it works like in 8.4
  Y N - this was broken in 8.4 ("at" was ineffective and it was finding
        all subterms syntactically equal to the first one which matches)
  N Y Y it now finds all subterms like the first one which matches
        while in 8.4 it used to fail (I hope it is not a too risky in-draft
        for a semantics we would regret...) (e.g. "destruct (S _)" on
        goal "S x = S y + S x" now selects the two occurrences of "S x"
        while it was failing before)
  N Y N it works like in 8.4
  N N - it works like in 8.4, selecting all subterms like the
        first one which matches
- Note that the "historical" semantics, when looking for a subterm, to
  select all subterms that syntactically match the first subterm to
  match the pattern (looking from left to right) is now internally called
  "like first".
- Selection of subterms can now find the type by pattern-matching (useful e.g.
  for "induction (nat_rect _ _ _ _)")
- A version of Unification.w_unify w/o any conversion is used for
  finding the subterm: it could be easily replaced by an other
  matching algorithm.

In particular, "destruct H" now works on a goal such as "H:True -> x<=y |- P y".

Secondary change is in the interpretation of terms with existential
variables:
- When several arguments are given, interpretation is delayed at the
  time of execution
- Because we aim at eventually accepting "edestruct c" with unresolved
  holes in c, we need the sigma obtained from c to be an extension of
  the sigma of the tactics, while before, we just type-checked c
  independently of the sigma of the tactic
- Finishing the resolution of evars (using type classes, candidates,
  pending conversion problems) is made slightly cleaner: it now takes
  three states: a term is evaluated in state sigma, leading to state
  sigma' >= sigma, with evars finally solved in state sigma'' >=
  sigma'; we solve evars in the diff of sigma' and sigma and report
  the solution in sigma''
- We however renounce to give now a success semantics to "edestruct c"
  when "c" has unresolved holes, waiting instead for a decision on
  what to do in the case of a similar eapply (see mail to coqdev).

An auxiliary change is that an "in" clause can be attached to each component
of a "destruct t, u, v", etc.

Incidentally, make_abstraction does not do evar resolution itself any longer.

2 files changed, 9 insertions, 3 deletions

diff --git a/intf/locus.mli b/intf/locus.mli
index e0ce43331e..35b7380645 100644
--- a/intf/locus.mli
+++ b/intf/locus.mli
@@ -86,3 +86,9 @@ type goal_location = hyp_location option
    the conclusion (conclusion is represented by None) *)
 
 type simple_clause = Id.t option list
+
+(** {6 A notion of occurrences allowing to express "all occurrences
+       convertible to the first which matches"} *)
+
+type 'a or_like_first = AtOccs of 'a | LikeFirst
+
diff --git a/intf/tacexpr.mli b/intf/tacexpr.mli
index 2967c10dd7..c8c7e28e9f 100644
--- a/intf/tacexpr.mli
+++ b/intf/tacexpr.mli
@@ -56,15 +56,15 @@ type 'id message_token =
   | MsgInt of int
   | MsgIdent of 'id
 
-type 'constr induction_clause =
+type ('constr,'id) induction_clause =
     'constr with_bindings induction_arg *
     (intro_pattern_naming_expr located option (* eqn:... *)
     * 'constr or_and_intro_pattern_expr located or_var option) (* as ... *)
+    * 'id clause_expr option (* in ... *)
 
 type ('constr,'id) induction_clause_list =
-    'constr induction_clause list
+    ('constr,'id) induction_clause list
     * 'constr with_bindings option (* using ... *)
-    * 'id clause_expr option (* in ... *)
 
 type 'a with_bindings_arg = clear_flag * 'a with_bindings