lean2/src/library/tactic/inversion_tactic.cpp

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/*
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 "kernel/instantiate.h"
#include "kernel/inductive/inductive.h"
#include "library/locals.h"
#include "library/tactic/tactic.h"
#include "library/reducible.h"
#include "library/tactic/expr_to_tactic.h"
namespace lean {
static bool is_inversion_applicable(environment const & env, expr const & t) {
expr const & fn = get_app_fn(t);
if (!is_constant(fn))
return false;
if (!inductive::is_inductive_decl(env, const_name(fn)))
return false;
if (!env.find(name{const_name(fn), "cases_on"}) ||
!env.find(name("eq")) || !env.find(name("heq")))
return false;
return true;
}
static pair<expr, expr> mk_eq(type_checker & tc, expr const & lhs, expr const & rhs) {
expr lhs_type = tc.infer(lhs).first;
expr rhs_type = tc.infer(rhs).first;
constraint_seq cs;
if (tc.is_def_eq(lhs_type, rhs_type, justification(), cs) && !cs) {
level l = sort_level(tc.ensure_type(lhs_type).first);
return mk_pair(mk_app(mk_constant("eq", to_list(l)), lhs_type, lhs, rhs),
mk_app(mk_constant({"eq", "refl"}, to_list(l)), rhs_type, rhs));
} else {
level l = sort_level(tc.ensure_type(lhs_type).first);
return mk_pair(mk_app(mk_constant("heq", to_list(l)), lhs_type, lhs, rhs_type, rhs),
mk_app(mk_constant({"heq", "refl"}, to_list(l)), rhs_type, rhs));
}
}
tactic generalize_indices_tactic(name const & n) {
auto fn = [=](environment const & env, 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);
auto p = g.find_hyp(n);
if (!p)
return none_proof_state();
expr const & h = p->first;
name_generator ngen = s.get_ngen();
auto tc = mk_type_checker(env, ngen.mk_child(), s.relax_main_opaque());
expr h_type = tc->whnf(mlocal_type(h)).first;
if (!is_inversion_applicable(env, h_type))
return none_proof_state();
buffer<expr> hyps;
g.get_hyps(hyps);
expr m = g.get_meta();
expr m_type = g.get_type();
auto new_subst = s.get_subst();
name h_new_name = g.get_unused_name(local_pp_name(h));
buffer<expr> I_args;
expr const & I = get_app_args(h_type, I_args);
// Set 1. generalize indices
unsigned nindices = *inductive::get_num_indices(env, const_name(I));
if (nindices > 0) {
expr h_new_type = mk_app(I, I_args.size() - nindices, I_args.data());
expr d = tc->whnf(tc->infer(h_new_type).first).first;
unsigned eq_idx = 1;
name eq_prefix("H");
buffer<expr> ts;
buffer<expr> eqs;
buffer<expr> refls;
for (unsigned i = I_args.size() - nindices; i < I_args.size(); i++) {
expr t_type = binding_domain(d);
expr t = mk_local(ngen.next(), g.get_unused_name(binding_name(d)), t_type, binder_info());
expr const & index = I_args[i];
pair<expr, expr> p = mk_eq(*tc, t, index);
expr new_eq = p.first;
expr new_refl = p.second;
eqs.push_back(mk_local(ngen.next(), g.get_unused_name(eq_prefix, eq_idx), new_eq, binder_info()));
refls.push_back(new_refl);
h_new_type = mk_app(h_new_type, t);
hyps.push_back(t);
ts.push_back(t);
d = instantiate(binding_body(d), t);
}
expr h_new = mk_local(ngen.next(), h_new_name, h_new_type, local_info(h));
hyps.push_back(h_new);
expr new_type = Pi(eqs, g.get_type());
expr new_meta = mk_app(mk_metavar(ngen.next(), Pi(hyps, new_type)), hyps);
goal new_g(new_meta, new_type);
expr val = g.abstract(mk_app(mk_app(mk_app(Fun(ts, Fun(h_new, new_meta)), nindices, I_args.end() - nindices), h), refls));
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);
} else {
expr h_new = mk_local(ngen.next(), h_new_name, h_type, local_info(h));
hyps.push_back(h_new);
expr new_meta = mk_app(mk_metavar(ngen.next(), Pi(hyps, g.get_type())), hyps);
goal new_g(new_meta, g.get_type());
expr val = g.abstract(mk_app(new_meta, h));
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 tactic01(fn);
}
tactic cases_on_tactic() {
// TODO(Leo)
return id_tactic();
}
tactic inversion_eqs_tactic() {
// TODO(Leo)
return id_tactic();
}
tactic inversion_clear_tactic() {
// TODO(Leo)
return id_tactic();
}
tactic inversion_tactic(name const & n) {
return generalize_indices_tactic(n) << cases_on_tactic() << inversion_eqs_tactic() << inversion_clear_tactic();
}
void initialize_inversion_tactic() {
register_tac(name({"tactic", "inversion"}),
[](type_checker &, elaborate_fn const &, expr const & e, pos_info_provider const *) {
name n = tactic_expr_to_id(app_arg(e), "invalid 'inversion' tactic, argument must be an identifier");
return inversion_tactic(n);
});
}
void finalize_inversion_tactic() {}
}