feat(library/tactic): add 'clear' tactic, closes #341

src/library/locals.cpp

@@ -7,6 +7,7 @@ Author: Leonardo de Moura
 #include "util/name_set.h"
 #include "kernel/expr.h"
 #include "kernel/for_each_fn.h"
+#include "kernel/find_fn.h"
 
 namespace lean {
 void collect_univ_params_core(level const & l, name_set & r) {
@@ -58,4 +59,21 @@ void collect_locals(expr const & e, expr_struct_set & ls) {
             return true;
         });
 }
+
+bool contains_local(expr const & e, name const & n) {
+    if (!has_local(e))
+        return false;
+    bool result = false;
+    for_each(e, [&](expr const & e, unsigned) {
+            if (result || !has_local(e))  {
+                return false;
+            } else if (is_local(e) && mlocal_name(e) == n) {
+                result = true;
+                return false;
+            } else {
+                return true;
+            }
+        });
+    return result;
+}
 }

src/library/locals.h

@@ -22,4 +22,7 @@ template<typename It> bool contains_local(expr const & local, It const & begin_l
 inline bool contains_local(expr const & local, buffer<expr> const & locals) {
     return contains_local(local, locals.begin(), locals.end());
 }
+
+/** \brief Return true iff \c e contains a local constant named \c n (it uses mlocal_name) */
+bool contains_local(expr const & e, name const & n);
 }

src/library/tactic/CMakeLists.txt

@@ -1,6 +1,6 @@
 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
-expr_to_tactic.cpp util.cpp init_module.cpp)
+clear_tactic.cpp expr_to_tactic.cpp util.cpp init_module.cpp)
 
 target_link_libraries(tactic ${LEAN_LIBS})

src/library/tactic/clear_tactic.cpp

@@ -0,0 +1,67 @@
+/*
+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 clear_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
+                }
+                if (contains_local(g.get_type(), real_n))
+                    return none_proof_state(); // type 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_meta = mk_app(mk_metavar(ngen.next(), Pi(new_locals, g.get_type())), new_locals);
+                goal new_g(new_meta, g.get_type());
+                expr val      = Fun(locals, new_meta);
+                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_clear_arg(expr const & e) {
+    return tactic_expr_to_id(e, "invalid 'clear' tactic, argument must be an identifier");
+}
+
+void initialize_clear_tactic() {
+    register_tac(name({"tactic", "clear"}),
+                 [](type_checker &, elaborate_fn const &, expr const & e, pos_info_provider const *) {
+                     name n = get_clear_arg(app_arg(e));
+                     return clear_tactic(n);
+                 });
+}
+void finalize_clear_tactic() {}
+}

src/library/tactic/clear_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 clear_tactic(name const & n);
+void initialize_clear_tactic();
+void finalize_clear_tactic();
+}

src/library/tactic/init_module.cpp

@@ -15,6 +15,7 @@ Author: Leonardo de Moura
 #include "library/tactic/unfold_tactic.h"
 #include "library/tactic/generalize_tactic.h"
 #include "library/tactic/whnf_tactic.h"
+#include "library/tactic/clear_tactic.h"
 
 namespace lean {
 void initialize_tactic_module() {
@@ -29,9 +30,11 @@ void initialize_tactic_module() {
     initialize_unfold_tactic();
     initialize_generalize_tactic();
     initialize_whnf_tactic();
+    initialize_clear_tactic();
 }
 
 void finalize_tactic_module() {
+    finalize_clear_tactic();
     finalize_whnf_tactic();
     finalize_generalize_tactic();
     finalize_unfold_tactic();

tests/lean/run/clear_tac.lean

@@ -0,0 +1,17 @@
+import logic
+
+example {a b c : Prop} : a → b → c → a ∧ b :=
+begin
+  intros (Ha, Hb, Hc),
+  clear Hc,
+  clear c,
+  apply (and.intro Ha Hb),
+end
+
+example {a b c : Prop} : a → b → c → c ∧ b :=
+begin
+  intros (Ha, Hb, Hc),
+  clear Ha,
+  clear a,
+  apply (and.intro Hc Hb),
+end