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// 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)
//[ transform_terminals
#include <boost/yap/yap.hpp>
struct iota_terminal_transform
{
// Base case. Note that we're not treating placeholders specially for this
// example (they're easy to special-case if necessary).
template<typename T>
auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::terminal>, T && t)
{
// Like the std::iota() algorithm, we create replacement int terminals
// with the values index_, index_ + 1, index_ + 2, etc.
return boost::yap::make_terminal(index_++);
}
// Recursive case: Match any call expression.
template<typename CallableExpr, typename... Arg>
auto operator()(boost::yap::expr_tag<boost::yap::expr_kind::call>,
CallableExpr callable, Arg &&... arg)
{
// Even though the callable in a call expression is technically a
// terminal, it doesn't make a lot of sense to replace it with an int,
// so we'll only transform the argument subexpressions.
return boost::yap::make_expression<boost::yap::expr_kind::call>(
boost::yap::as_expr(callable),
boost::yap::transform(boost::yap::as_expr(arg), *this)...);
}
int index_;
};
int sum(int a, int b) { return a + b; }
int main()
{
{
// This simple sum(8, 8) expression requires both overloads of
// iota_terminal_transform.
auto expr = boost::yap::make_terminal(sum)(8, 8);
assert(evaluate(expr) == 16);
auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{1});
assert(evaluate(iota_expr) == 3);
}
{
// This expression requires only the terminal case of
// iota_terminal_transform.
auto expr = -(boost::yap::make_terminal(8) + 8);
assert(evaluate(expr) == -16);
auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{0});
assert(evaluate(iota_expr) == -1);
}
{
// Like the first expression above, this expression requires both
// overloads of iota_terminal_transform.
auto expr = boost::yap::make_terminal(sum)(-(boost::yap::make_terminal(8) + 8), 0);
assert(evaluate(expr) == -16);
auto iota_expr = boost::yap::transform(expr, iota_terminal_transform{0});
assert(evaluate(iota_expr) == -3);
}
}
//]
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