101 lines
3.1 KiB
C++
101 lines
3.1 KiB
C++
// Copyright (C) 2016-2018 T. Zachary Laine
|
|
//
|
|
// Distributed under the Boost Software License, Version 1.0. (See
|
|
// accompanying file LICENSE_1_0.txt or copy at
|
|
// http://www.boost.org/LICENSE_1_0.txt)
|
|
//[ calc3
|
|
#include <boost/yap/expression.hpp>
|
|
|
|
#include <boost/hana/maximum.hpp>
|
|
|
|
#include <iostream>
|
|
|
|
|
|
// Look! A transform! This one transforms the expression tree into the arity
|
|
// of the expression, based on its placeholders.
|
|
//[ calc3_get_arity_xform
|
|
struct get_arity
|
|
{
|
|
// Base case 1: Match a placeholder terminal, and return its arity as the
|
|
// result.
|
|
template <long long I>
|
|
boost::hana::llong<I> operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>,
|
|
boost::yap::placeholder<I>)
|
|
{ return boost::hana::llong_c<I>; }
|
|
|
|
// Base case 2: Match any other terminal. Return 0; non-placeholders do
|
|
// not contribute to arity.
|
|
template <typename T>
|
|
auto operator() (boost::yap::expr_tag<boost::yap::expr_kind::terminal>, T &&)
|
|
{
|
|
using namespace boost::hana::literals;
|
|
return 0_c;
|
|
}
|
|
|
|
// Recursive case: Match any expression not covered above, and return the
|
|
// maximum of its children's arities.
|
|
template <boost::yap::expr_kind Kind, typename... Arg>
|
|
auto operator() (boost::yap::expr_tag<Kind>, Arg &&... arg)
|
|
{
|
|
return boost::hana::maximum(
|
|
boost::hana::make_tuple(
|
|
boost::yap::transform(
|
|
boost::yap::as_expr(std::forward<Arg>(arg)),
|
|
get_arity{}
|
|
)...
|
|
)
|
|
);
|
|
}
|
|
};
|
|
//]
|
|
|
|
int main ()
|
|
{
|
|
using namespace boost::yap::literals;
|
|
|
|
// These lambdas wrap our expressions as callables, and allow us to check
|
|
// the arity of each as we call it.
|
|
|
|
auto expr_1 = 1_p + 2.0;
|
|
|
|
auto expr_1_fn = [expr_1](auto &&... args) {
|
|
auto const arity = boost::yap::transform(expr_1, get_arity{});
|
|
static_assert(arity.value == sizeof...(args), "Called with wrong number of args.");
|
|
return evaluate(expr_1, args...);
|
|
};
|
|
|
|
auto expr_2 = 1_p * 2_p;
|
|
|
|
auto expr_2_fn = [expr_2](auto &&... args) {
|
|
auto const arity = boost::yap::transform(expr_2, get_arity{});
|
|
static_assert(arity.value == sizeof...(args), "Called with wrong number of args.");
|
|
return evaluate(expr_2, args...);
|
|
};
|
|
|
|
auto expr_3 = (1_p - 2_p) / 2_p;
|
|
|
|
auto expr_3_fn = [expr_3](auto &&... args) {
|
|
auto const arity = boost::yap::transform(expr_3, get_arity{});
|
|
static_assert(arity.value == sizeof...(args), "Called with wrong number of args.");
|
|
return evaluate(expr_3, args...);
|
|
};
|
|
|
|
// Displays "5"
|
|
std::cout << expr_1_fn(3.0) << std::endl;
|
|
|
|
// Displays "6"
|
|
std::cout << expr_2_fn(3.0, 2.0) << std::endl;
|
|
|
|
// Displays "0.5"
|
|
std::cout << expr_3_fn(3.0, 2.0) << std::endl;
|
|
|
|
// Static-asserts with "Called with wrong number of args."
|
|
//std::cout << expr_3_fn(3.0) << std::endl;
|
|
|
|
// Static-asserts with "Called with wrong number of args."
|
|
//std::cout << expr_3_fn(3.0, 2.0, 1.0) << std::endl;
|
|
|
|
return 0;
|
|
}
|
|
//]
|