lean2/src/library/fo_unify.cpp

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/*
Copyright (c) 2013 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Author: Leonardo de Moura
*/
#include <utility>
#include "kernel/builtin.h"
#include "library/fo_unify.h"
#include "library/expr_pair.h"
#include "library/kernel_bindings.h"
namespace lean {
static void assign(substitution & s, expr const & mvar, expr const & e) {
lean_assert(is_metavar(mvar));
s.insert(metavar_name(mvar), e);
}
static bool is_metavar_wo_local_context(expr const & e) {
return is_metavar(e) && !metavar_lctx(e);
}
static bool is_eq_heq(expr const & e, expr & lhs, expr & rhs) {
return is_eq(e, lhs, rhs) || is_homo_eq(e, lhs, rhs);
}
optional<substitution> fo_unify(expr e1, expr e2) {
lean_assert(e1);
lean_assert(e2);
substitution s;
unsigned i;
expr lhs1, rhs1, lhs2, rhs2;
buffer<expr_pair> todo;
todo.emplace_back(e1, e2);
while (!todo.empty()) {
auto p = todo.back();
todo.pop_back();
e1 = find(s, p.first);
e2 = find(s, p.second);
if (e1 != e2) {
if (is_metavar_wo_local_context(e1)) {
assign(s, e1, e2);
} else if (is_metavar_wo_local_context(e2)) {
assign(s, e2, e1);
} else if (is_eq_heq(e1, lhs1, rhs1) && is_eq_heq(e2, lhs2, rhs2)) {
todo.emplace_back(lhs1, lhs2);
todo.emplace_back(rhs1, rhs2);
} else {
if (e1.kind() != e2.kind())
return optional<substitution>();
switch (e1.kind()) {
case expr_kind::Var: case expr_kind::Constant: case expr_kind::Type: case expr_kind::Value: case expr_kind::MetaVar:
return optional<substitution>();
case expr_kind::App:
if (num_args(e1) != num_args(e2))
return optional<substitution>();
i = num_args(e1);
while (i > 0) {
--i;
todo.emplace_back(arg(e1, i), arg(e2, i));
}
break;
case expr_kind::Eq:
lean_unreachable(); break; // LCOV_EXCL_LINE
case expr_kind::Lambda: case expr_kind::Pi:
todo.emplace_back(abst_body(e1), abst_body(e2));
todo.emplace_back(abst_domain(e1), abst_domain(e2));
break;
case expr_kind::Let:
todo.emplace_back(let_body(e1), let_body(e2));
todo.emplace_back(let_value(e1), let_value(e2));
if (static_cast<bool>(let_type(e1)) != static_cast<bool>(let_type(e2)))
return optional<substitution>();
if (let_type(e1)) {
lean_assert(let_type(e2));
todo.emplace_back(let_type(e1), let_type(e2));
}
break;
}
}
}
}
return optional<substitution>(s);
}
static int fo_unify(lua_State * L) {
optional<substitution> r = fo_unify(to_nonnull_expr(L, 1), to_nonnull_expr(L, 2));
if (!r) {
lua_pushnil(L);
return 1;
} else {
return push_substitution(L, *r);
}
}
void open_fo_unify(lua_State * L) {
SET_GLOBAL_FUN(fo_unify, "fo_unify");
}
}