reduce.hpp

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#pragma once

#include <atria/xform/any_state.hpp>
#include <atria/xform/impure/abort_reduce.hpp>
#include <atria/xform/detail/reduce_nested_non_empty.hpp>
#include <atria/xform/detail/is_non_empty.hpp>

namespace atria {
namespace xform {
namespace impure {

namespace detail {

template <typename ResultT, typename ArgT>
auto from_any_state(ArgT&& s)
  -> estd::enable_if_t<std::is_same<estd::decay_t<ArgT>, any_state>{},
                       estd::decay_t<ResultT> >
{
  return std::forward<ArgT>(s).template as<ResultT>();
}

template <typename ResultT, typename ArgT>
auto from_any_state(ArgT&& s)
  -> estd::enable_if_t<!std::is_same<estd::decay_t<ArgT>, any_state>{},
                       ArgT&&>
{
  return std::forward<ArgT>(s);
}

} // namespace detail

template <typename ReducingFnT,
          typename StateT,
          typename ...InputRangeTs>
auto reduce(ReducingFnT&& step, StateT&& state, InputRangeTs&& ...ranges)
  -> estd::decay_t<StateT>
{
  try {
    return detail::from_any_state<StateT>(
      xform::detail::is_non_empty(ranges...)
        ? state_complete(
          xform::detail::reduce_nested_non_empty(
            std::forward<ReducingFnT>(step),
            std::forward<StateT>(state),
            std::forward<InputRangeTs>(ranges)...))
        : std::forward<StateT>(state));
  } catch (reduce_aborted_error<estd::decay_t<StateT> >& err) {
    return std::move(err.result);
  } catch (reduce_aborted_error<any_state>& err) {
    return std::move(err.result).as<StateT>();
  }
}

} // namespace impure
} // namespace xform
} // namespace atria