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lean2/src/frontends/lean/placeholder_elaborator.cpp
Leonardo de Moura c775da16ec feat(frontends/lean/elaborator): discard partial solution during 
class-instance resolution, use only tactic_hints associated with
classes, enforce is_strict
2014-09-25 19:46:08 -07:00

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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 "util/lazy_list_fn.h"
#include "util/flet.h"
#include "kernel/instantiate.h"
#include "kernel/for_each_fn.h"
#include "kernel/abstract.h"
#include "library/unifier.h"
#include "library/reducible.h"
#include "library/metavar_closure.h"
#include "library/error_handling/error_handling.h"
#include "frontends/lean/util.h"
#include "frontends/lean/class.h"
#include "frontends/lean/tactic_hint.h"
#include "frontends/lean/local_context.h"
#include "frontends/lean/choice_iterator.h"
namespace lean {
/** \brief Context for handling placeholder metavariable choice constraint */
struct placeholder_context {
io_state m_ios;
name_generator m_ngen;
type_checker_ptr m_tc;
local_context m_ctx;
bool m_relax;
bool m_use_local_instances;
placeholder_context(environment const & env, io_state const & ios, local_context const & ctx,
name const & prefix, bool relax, bool use_local_instances):
m_ios(ios),
m_ngen(prefix),
m_tc(mk_type_checker(env, m_ngen.mk_child(), relax)),
m_ctx(ctx),
m_relax(relax),
m_use_local_instances(use_local_instances) {
}
environment const & env() const { return m_tc->env(); }
io_state const & ios() const { return m_ios; }
bool use_local_instances() const { return m_use_local_instances; }
type_checker & tc() const { return *m_tc; }
};
pair<expr, constraint> mk_placeholder_elaborator(std::shared_ptr<placeholder_context> const & C,
optional<expr> const & type, tag g);
/** \brief Whenever the elaborator finds a placeholder '_' or introduces an
implicit argument, it creates a metavariable \c ?m. It also creates a
delayed choice constraint (?m in fn).
The function \c fn produces a stream of alternative solutions for ?m.
In this case, \c fn will do the following:
1) if the elaborated type of ?m is a 'class' C, then the stream will start with
a) all local instances of class C (if elaborator.local_instances == true)
b) solutions produced by tactic_hints for class C
2) if the elaborated type of ?m is not a class, then the stream will only contain
the solutions produced by tactic_hints.
The unifier only process delayed choice constraints when there are no other kind
of constraint to be processed.
This is a helper class for implementing this choice function.
*/
struct placeholder_elaborator : public choice_iterator {
std::shared_ptr<placeholder_context> m_C;
expr m_meta;
// elaborated type of the metavariable
expr m_meta_type;
// local instances that should also be included in the
// class-instance resolution.
// This information is retrieved from the local context
list<expr> m_local_instances;
// global declaration names that are class instances.
// This information is retrieved using #get_class_instances.
list<name> m_instances;
// Tactic hints for the class
list<tactic_hint_entry> m_tactics;
// result produce by last executed tactic.
proof_state_seq m_tactic_result;
justification m_jst;
placeholder_elaborator(std::shared_ptr<placeholder_context> const & C,
expr const & meta, expr const & meta_type,
list<expr> const & local_insts, list<name> const & instances,
list<tactic_hint_entry> const & tacs,
justification const & j):
choice_iterator(), m_C(C),
m_meta(meta), m_meta_type(meta_type),
m_local_instances(local_insts), m_instances(instances),
m_tactics(tacs),
m_jst(j) {
}
constraints mk_constraints(constraint const & c, buffer<constraint> const & cs) {
return cons(c, to_list(cs.begin(), cs.end()));
}
optional<constraints> try_instance(expr const & inst, expr const & inst_type) {
type_checker & tc = m_C->tc();
name_generator & ngen = m_C->m_ngen;
tag g = inst.get_tag();
local_context & ctx = m_C->m_ctx;
try {
flet<local_context> scope(ctx, ctx);
buffer<expr> locals;
expr meta_type = m_meta_type;
while (true) {
meta_type = tc.whnf(meta_type).first;
if (!is_pi(meta_type))
break;
expr local = mk_local(ngen.next(), binding_name(meta_type),
binding_domain(meta_type), binding_info(meta_type));
ctx.add_local(local);
locals.push_back(local);
meta_type = instantiate(binding_body(meta_type), local);
}
expr type = inst_type;
expr r = inst;
buffer<constraint> cs;
while (true) {
type = tc.whnf(type).first;
if (!is_pi(type))
break;
pair<expr, constraint> ac = mk_placeholder_elaborator(m_C, some_expr(binding_domain(type)), g);
expr arg = ac.first;
cs.push_back(ac.second);
r = mk_app(r, arg).set_tag(g);
type = instantiate(binding_body(type), arg);
}
r = Fun(locals, r);
bool relax = m_C->m_relax;
constraint c = mk_eq_cnstr(m_meta, r, m_jst, relax);
return optional<constraints>(mk_constraints(c, cs));
} catch (exception &) {
return optional<constraints>();
}
}
optional<constraints> try_instance(name const & inst) {
environment const & env = m_C->env();
if (auto decl = env.find(inst)) {
name_generator & ngen = m_C->m_ngen;
buffer<level> ls_buffer;
unsigned num_univ_ps = length(decl->get_univ_params());
for (unsigned i = 0; i < num_univ_ps; i++)
ls_buffer.push_back(mk_meta_univ(ngen.next()));
levels ls = to_list(ls_buffer.begin(), ls_buffer.end());
expr inst_cnst = copy_tag(m_meta, mk_constant(inst, ls));
expr inst_type = instantiate_type_univ_params(*decl, ls);
return try_instance(inst_cnst, inst_type);
} else {
return optional<constraints>();
}
}
optional<constraints> get_next_tactic_result() {
while (auto next = m_tactic_result.pull()) {
m_tactic_result = next->second;
if (!empty(next->first.get_goals()))
continue; // has unsolved goals
substitution subst = next->first.get_subst();
expr const & mvar = get_app_fn(m_meta);
bool relax = m_C->m_relax;
constraints cs = metavar_closure(m_meta_type).mk_constraints(subst, m_jst, relax);
constraint c = mk_eq_cnstr(mvar, subst.instantiate(mvar), m_jst, relax);
return some(cons(c, cs));
}
return optional<constraints>();
}
virtual optional<constraints> next() {
while (!empty(m_local_instances)) {
expr inst = head(m_local_instances);
m_local_instances = tail(m_local_instances);
if (!is_local(inst))
continue;
if (auto r = try_instance(inst, mlocal_type(inst)))
return r;
}
while (!empty(m_instances)) {
name inst = head(m_instances);
m_instances = tail(m_instances);
if (auto cs = try_instance(inst))
return cs;
}
if (auto cs = get_next_tactic_result())
return cs;
while (!empty(m_tactics)) {
tactic const & tac = head(m_tactics).get_tactic();
m_tactics = tail(m_tactics);
proof_state ps(goals(goal(m_meta, m_meta_type)), substitution(), m_C->m_ngen.mk_child());
try {
m_tactic_result = tac(m_C->env(), m_C->ios(), ps);
if (auto cs = get_next_tactic_result())
return cs;
} catch (exception &) {}
}
return optional<constraints>();
}
};
constraint mk_placeholder_cnstr(std::shared_ptr<placeholder_context> const & C, expr const & m) {
environment const & env = C->env();
justification j = mk_failed_to_synthesize_jst(env, m);
auto choice_fn = [=](expr const & meta, expr const & meta_type, substitution const & s,
name_generator const & /* ngen */) {
expr const & mvar = get_app_fn(meta);
if (auto cls_name_it = is_ext_class(C->tc(), meta_type)) {
name cls_name = *cls_name_it;
list<expr> const & ctx = C->m_ctx.get_data();
list<expr> local_insts;
if (C->use_local_instances())
local_insts = get_local_instances(C->tc(), ctx, cls_name);
list<name> insts = get_class_instances(env, cls_name);
list<tactic_hint_entry> tacs;
if (!s.is_assigned(mvar))
tacs = get_tactic_hints(env, cls_name);
if (empty(local_insts) && empty(insts) && empty(tacs))
return lazy_list<constraints>(); // nothing to be done
// we are always strict with placeholders associated with classes
return choose(std::make_shared<placeholder_elaborator>(C, meta, meta_type, local_insts, insts, tacs, j));
} else {
// do nothing, type is not a class...
return lazy_list<constraints>(constraints());
}
};
bool owner = false;
bool relax = C->m_relax;
return mk_choice_cnstr(m, choice_fn, to_delay_factor(cnstr_group::ClassInstance),
owner, j, relax);
}
pair<expr, constraint> mk_placeholder_elaborator(std::shared_ptr<placeholder_context> const & C,
optional<expr> const & type, tag g) {
expr m = C->m_ctx.mk_meta(C->m_ngen, type, g);
constraint c = mk_placeholder_cnstr(C, m);
return mk_pair(m, c);
}
/** \brief Similar to has_expr_metavar, but ignores metavariables occurring in the type
of local constants */
static bool has_expr_metavar_relaxed(expr const & e) {
if (!has_expr_metavar(e))
return false;
bool found = false;
for_each(e, [&](expr const & e, unsigned) {
if (found || !has_expr_metavar(e))
return false;
if (is_metavar(e)) {
found = true;
return false;
}
if (is_local(e))
return false; // do not visit type
return true;
});
return found;
}
constraint mk_placeholder_root_cnstr(std::shared_ptr<placeholder_context> const & C, expr const & m, bool is_strict,
unifier_config const & cfg, unsigned delay_factor) {
environment const & env = C->env();
justification j = mk_failed_to_synthesize_jst(env, m);
auto choice_fn = [=](expr const & meta, expr const & meta_type, substitution const & s,
name_generator const & ngen) {
if (has_expr_metavar_relaxed(meta_type)) {
if (delay_factor < to_delay_factor(cnstr_group::ClassInstance)) {
constraint delayed_c = mk_placeholder_root_cnstr(C, m, is_strict, cfg, delay_factor+1);
return lazy_list<constraints>(constraints(delayed_c));
}
}
if (!is_ext_class(C->tc(), meta_type)) {
// do nothing, since type is not a class.
return lazy_list<constraints>(constraints());
}
pair<expr, justification> mj = update_meta(meta, s);
expr new_meta = mj.first;
justification new_j = mj.second;
constraint c = mk_placeholder_cnstr(C, new_meta);
unifier_config new_cfg(cfg);
new_cfg.m_discard = false;
new_cfg.m_use_exceptions = false;
unify_result_seq seq1 = unify(env, 1, &c, ngen, new_cfg);
unify_result_seq seq2 = filter(seq1, [=](pair<substitution, constraints> const & p) {
substitution new_s = p.first;
expr result = new_s.instantiate(new_meta);
// We only keep complete solution (modulo universe metavariables)
return !has_expr_metavar_relaxed(result);
});
lazy_list<constraints> seq3 = map2<constraints>(seq2, [=](pair<substitution, constraints> const & p) {
substitution new_s = p.first;
// some constraints may have been postponed (example: universe level constraints)
constraints postponed = map(p.second,
[&](constraint const & c) {
// we erase internal justifications
return update_justification(c, new_j);
});
metavar_closure cls(new_meta);
cls.add(meta_type);
bool relax = C->m_relax;
constraints cs = cls.mk_constraints(new_s, new_j, relax);
return append(cs, postponed);
});
if (is_strict) {
return seq3;
} else {
// make sure it does not fail by appending empty set of constraints
return append(seq3, lazy_list<constraints>(constraints()));
}
};
bool owner = false;
bool relax = C->m_relax;
return mk_choice_cnstr(m, choice_fn, delay_factor, owner, j, relax);
}
/** \brief Create a metavariable, and attach choice constraint for generating
solutions using class-instances and tactic-hints.
*/
pair<expr, constraint> mk_placeholder_elaborator(
environment const & env, io_state const & ios, local_context const & ctx,
name const & prefix, bool relax, bool use_local_instances,
bool is_strict, optional<expr> const & type, tag g, unifier_config const & cfg) {
auto C = std::make_shared<placeholder_context>(env, ios, ctx, prefix, relax, use_local_instances);
expr m = C->m_ctx.mk_meta(C->m_ngen, type, g);
constraint c = mk_placeholder_root_cnstr(C, m, is_strict, cfg, to_delay_factor(cnstr_group::Basic));
return mk_pair(m, c);
}
}
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