feat(library/tactic): add 'revert' tactic, closes #346

library/tools/tactic.lean

@@ -65,6 +65,7 @@ opaque definition generalize_list (es : expr_list) : tactic := builtin
 notation `generalizes` `(` l:(foldr `,` (h t, expr_list.cons h t) expr_list.nil) `)` := generalize_list l
 
 opaque definition clear (e : expr) : tactic := builtin
+opaque definition revert (e : expr) : tactic := builtin
 
 opaque definition unfold      (e : expr) : tactic := builtin
 opaque definition exact       (e : expr) : tactic := builtin

src/library/tactic/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_library(tactic goal.cpp proof_state.cpp tactic.cpp elaborate.cpp
 apply_tactic.cpp intros_tactic.cpp rename_tactic.cpp trace_tactic.cpp
-exact_tactic.cpp unfold_tactic.cpp generalize_tactic.cpp whnf_tactic.cpp
-clear_tactic.cpp expr_to_tactic.cpp util.cpp init_module.cpp)
+exact_tactic.cpp unfold_tactic.cpp generalize_tactic.cpp
+whnf_tactic.cpp revert_tactic.cpp clear_tactic.cpp expr_to_tactic.cpp
+util.cpp init_module.cpp)
 
 target_link_libraries(tactic ${LEAN_LIBS})

src/library/tactic/init_module.cpp

@@ -16,6 +16,7 @@ Author: Leonardo de Moura
 #include "library/tactic/generalize_tactic.h"
 #include "library/tactic/whnf_tactic.h"
 #include "library/tactic/clear_tactic.h"
+#include "library/tactic/revert_tactic.h"
 
 namespace lean {
 void initialize_tactic_module() {
@@ -31,9 +32,11 @@ void initialize_tactic_module() {
     initialize_generalize_tactic();
     initialize_whnf_tactic();
     initialize_clear_tactic();
+    initialize_revert_tactic();
 }
 
 void finalize_tactic_module() {
+    finalize_revert_tactic();
     finalize_clear_tactic();
     finalize_whnf_tactic();
     finalize_generalize_tactic();

src/library/tactic/revert_tactic.cpp

@@ -0,0 +1,66 @@
+/*
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#include "kernel/abstract.h"
+#include "library/locals.h"
+#include "library/tactic/tactic.h"
+#include "library/tactic/expr_to_tactic.h"
+
+namespace lean {
+tactic revert_tactic(name const & n) {
+    auto fn = [=](environment const &, io_state const &, proof_state const & s) -> optional<proof_state> {
+        goals const & gs = s.get_goals();
+        if (empty(gs))
+            return none_proof_state();
+        goal  g          = head(gs);
+        goals tail_gs    = tail(gs);
+        expr meta        = g.get_meta();
+        buffer<expr> locals;
+        get_app_args(meta, locals);
+        unsigned i = locals.size();
+        while (i > 0) {
+            --i;
+            if (local_pp_name(locals[i]) == n) {
+                // found target
+                name real_n = mlocal_name(locals[i]);
+                for (unsigned j = i+1; j < locals.size(); j++) {
+                    if (contains_local(mlocal_type(locals[j]), real_n))
+                        return none_proof_state(); // other variables depends on n
+                }
+                buffer<expr> new_locals;
+                for (unsigned j = 0; j < i; j++)
+                    new_locals.push_back(locals[j]);
+                for (unsigned j = i+1; j < locals.size(); j++)
+                    new_locals.push_back(locals[j]);
+                name_generator ngen = s.get_ngen();
+                expr new_type = Pi(locals[i], g.get_type());
+                expr new_meta = mk_app(mk_metavar(ngen.next(), Pi(new_locals, new_type)), new_locals);
+                goal new_g(new_meta, new_type);
+                expr val      = Fun(locals, mk_app(new_meta, locals[i]));
+                substitution new_subst = s.get_subst();
+                new_subst.assign(g.get_name(), val);
+                proof_state new_s(s, goals(new_g, tail_gs), new_subst, ngen);
+                return some_proof_state(new_s);
+            }
+        }
+        return none_proof_state();
+    };
+    return tactic01(fn);
+}
+
+static name const & get_revert_arg(expr const & e) {
+    return tactic_expr_to_id(e, "invalid 'revert' tactic, argument must be an identifier");
+}
+
+void initialize_revert_tactic() {
+    register_tac(name({"tactic", "revert"}),
+                 [](type_checker &, elaborate_fn const &, expr const & e, pos_info_provider const *) {
+                     name n = get_revert_arg(app_arg(e));
+                     return revert_tactic(n);
+                 });
+}
+void finalize_revert_tactic() {}
+}

src/library/tactic/revert_tactic.h

@@ -0,0 +1,14 @@
+/*
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#pragma once
+#include "library/tactic/tactic.h"
+
+namespace lean {
+tactic revert_tactic(name const & n);
+void initialize_revert_tactic();
+void finalize_revert_tactic();
+}

tests/lean/run/revert_tac.lean

@@ -0,0 +1,27 @@
+import logic
+
+theorem tst {a b c : Prop} : a → b → c → a ∧ b :=
+begin
+  intros (Ha, Hb, Hc),
+  revert Ha,
+  intro Ha2,
+  apply (and.intro Ha2 Hb),
+end
+
+theorem foo1 {A : Type} (a b c : A) (P : A → Prop) : P a → a = b → P b :=
+begin
+  intros (Hp, Heq),
+  revert Hp,
+  apply (eq.rec_on Heq),
+  intro Hpa,
+  apply Hpa
+end
+
+theorem foo2 {A : Type} (a b c : A) (P : A → Prop) : P a → a = b → P b :=
+begin
+  intros (Hp, Heq),
+  apply (eq.rec_on Heq Hp)
+end
+
+print definition foo1
+print definition foo2