lean2/src/library/reduce.cpp
2013-09-19 22:40:34 -07:00

97 lines
2.7 KiB
C++

/*
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 "util/name_set.h"
#include "kernel/context.h"
#include "kernel/instantiate.h"
#include "kernel/environment.h"
#include "kernel/free_vars.h"
#include "kernel/replace.h"
#include "library/update_expr.h"
namespace lean {
bool is_head_beta(expr const & t) {
return is_app(t) && is_lambda(arg(t, 0));
}
expr head_beta_reduce(expr const & t) {
if (!is_head_beta(t)) {
return t;
} else {
unsigned num = num_args(t);
unsigned num1 = num - 1;
expr const * f = &arg(t, 0);
lean_assert(is_lambda(*f));
unsigned m = 1;
while (is_lambda(abst_body(*f)) && m < num1) {
f = &abst_body(*f);
m++;
}
lean_assert(m <= num1);
expr r = instantiate(abst_body(*f), m, &arg(t, 1));
if (m == num1) {
return r;
} else {
buffer<expr> args;
args.push_back(r);
m++;
for (; m < num; m++)
args.push_back(arg(t, m));
return mk_app(args.size(), args.data());
}
}
}
expr beta_reduce(expr t) {
auto f = [=](expr const & m, unsigned) -> expr {
if (is_head_beta(m))
return head_beta_reduce(m);
else
return m;
};
while (true) {
expr new_t = replace_fn<decltype(f)>(f)(t);
if (new_t == t)
return new_t;
else
t = new_t;
}
}
expr head_reduce(expr const & t, environment const & e, context const & c, name_set const * defs) {
if (is_head_beta(t)) {
return head_beta_reduce(t);
} else if (is_app(t)) {
expr f = arg(t, 0);
if (is_head_beta(f) || is_let(f) || is_constant(f) || is_var(f)) {
expr new_f = head_reduce(f, e, c, defs);
if (!is_eqp(f, new_f))
return update_app(t, 0, new_f);
else
return t;
} else {
return t;
}
} else if (is_var(t)) {
auto p = lookup_ext(c, var_idx(t));
context_entry const & ce = p.first;
if (ce.get_body()) {
return lift_free_vars(ce.get_body(), c.size() - p.second.size());
} else {
return t;
}
} else if (is_let(t)) {
return instantiate(let_body(t), let_value(t));
} else if (is_constant(t)) {
name const & n = const_name(t);
if (defs == nullptr || defs->find(n) != defs->end()) {
object const & obj = e.find_object(n);
if (obj && obj.is_definition() && !obj.is_opaque())
return obj.get_value();
}
}
return t;
}
}