lean2/src/frontends/lean/coercion_elaborator.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/type_checker.h"
#include "kernel/metavar.h"
#include "kernel/constraint.h"
#include "library/coercion.h"
#include "library/unifier.h"
#include "frontends/lean/choice_iterator.h"
#include "frontends/lean/coercion_elaborator.h"
namespace lean {
coercion_elaborator::coercion_elaborator(coercion_info_manager & info, expr const & arg,
list<constraints> const & choices, list<expr> const & coes,
bool use_id):
m_info(info), m_arg(arg), m_id(use_id), m_choices(choices), m_coercions(coes) {
lean_assert(!use_id || length(m_coercions) + 1 == length(m_choices));
lean_assert(use_id || length(m_coercions) == length(m_choices));
}
optional<constraints> coercion_elaborator::next() {
if (!m_choices)
return optional<constraints>();
if (m_id) {
m_id = false;
m_info.erase_coercion_info(m_arg);
} else if (m_coercions) {
expr c = head(m_coercions);
m_coercions = tail(m_coercions);
m_info.save_coercion_info(m_arg, mk_app(c, m_arg));
}
auto r = head(m_choices);
m_choices = tail(m_choices);
return optional<constraints>(r);
}
constraint mk_coercion_cnstr(type_checker & tc, coercion_info_manager & infom,
expr const & m, expr const & a, expr const & a_type,
justification const & j, unsigned delay_factor, bool relax) {
auto choice_fn = [=, &tc, &infom](expr const & meta, expr const & d_type, substitution const & s,
name_generator const & /* ngen */) {
expr new_a_type;
justification new_a_type_jst;
if (is_meta(a_type)) {
auto p = substitution(s).instantiate_metavars(a_type);
new_a_type = p.first;
new_a_type_jst = p.second;
} else {
new_a_type = a_type;
}
if (is_meta(new_a_type)) {
if (delay_factor < to_delay_factor(cnstr_group::DelayedChoice)) {
// postpone...
return lazy_list<constraints>(constraints(mk_coercion_cnstr(tc, infom, m, a, a_type, justification(),
delay_factor+1, relax)));
} else {
// giveup...
return lazy_list<constraints>(constraints(mk_eq_cnstr(meta, a, justification(), relax)));
}
}
constraint_seq cs;
new_a_type = tc.whnf(new_a_type, cs);
if (is_meta(d_type)) {
// case-split
buffer<std::tuple<name, expr, expr>> alts;
get_user_coercions(tc.env(), new_a_type, alts);
buffer<constraints> choices;
buffer<expr> coes;
// first alternative: no coercion
constraint_seq cs1 = cs + mk_eq_cnstr(meta, a, justification(), relax);
choices.push_back(cs1.to_list());
unsigned i = alts.size();
while (i > 0) {
--i;
auto const & t = alts[i];
expr coe = std::get<1>(t);
expr new_a = copy_tag(a, mk_app(coe, a));
coes.push_back(coe);
constraint_seq csi = cs + mk_eq_cnstr(meta, new_a, new_a_type_jst, relax);
choices.push_back(csi.to_list());
}
return choose(std::make_shared<coercion_elaborator>(infom, meta,
to_list(choices.begin(), choices.end()),
to_list(coes.begin(), coes.end())));
} else {
expr new_d_type = tc.whnf(d_type, cs);
expr const & d_cls = get_app_fn(new_d_type);
if (is_constant(d_cls)) {
list<expr> coes = get_coercions(tc.env(), new_a_type, const_name(d_cls));
if (is_nil(coes)) {
expr new_a = a;
infom.erase_coercion_info(a);
cs += mk_eq_cnstr(meta, new_a, new_a_type_jst, relax);
return lazy_list<constraints>(cs.to_list());
} else if (is_nil(tail(coes))) {
expr new_a = copy_tag(a, mk_app(head(coes), a));
infom.save_coercion_info(a, new_a);
cs += mk_eq_cnstr(meta, new_a, new_a_type_jst, relax);
return lazy_list<constraints>(cs.to_list());
} else {
list<constraints> choices = map2<constraints>(coes, [&](expr const & coe) {
expr new_a = copy_tag(a, mk_app(coe, a));
constraint c = mk_eq_cnstr(meta, new_a, new_a_type_jst, relax);
return (cs + c).to_list();
});
return choose(std::make_shared<coercion_elaborator>(infom, meta, choices, coes, false));
}
} else {
expr new_a = a;
infom.erase_coercion_info(a);
cs += mk_eq_cnstr(meta, new_a, new_a_type_jst, relax);
return lazy_list<constraints>(cs.to_list());
}
}
};
return mk_choice_cnstr(m, choice_fn, delay_factor, true, j, relax);
}
/** \brief Given a term <tt>a : a_type</tt>, and an expected type generate a metavariable with a delayed coercion. */
pair<expr, constraint> mk_coercion_elaborator(type_checker & tc, coercion_info_manager & infom, local_context & ctx,
bool relax, expr const & a, expr const & a_type, expr const & expected_type,
justification const & j) {
expr m = ctx.mk_meta(some_expr(expected_type), a.get_tag());
return mk_pair(m, mk_coercion_cnstr(tc, infom, m, a, a_type, j, to_delay_factor(cnstr_group::Basic), relax));
}
}