cpp-lazy-stream/stream.hpp

/*
 * File stream.hpp
 * 
 * Stream style functional composition
 *
 * @author Sam Jaffe
 *
 */

#include <algorithm>
#include <utility>
#include <functional>
#include <iterator>

namespace stream {

template <typename T> class stream {
  public:
    virtual ~stream() = default;
    //template<template <class...> class C>
    //C<T> complete() const; 
};

template <typename T, typename It>
class iter_stream : public stream<T> {
  public:
    virtual ~iter_stream() = default;
    template<template <class...> class C>
    C<T> complete() const { 
      C<T> out;
      std::copy(begin(), end(), std::back_inserter(out));
      return out;
    }
    typedef It const_iterator;
    virtual const_iterator begin() const = 0;
    virtual const_iterator end() const = 0;
};

template <typename T, template <class...> class C> 
class cont_stream : public iter_stream<T, typename C<T>::const_iterator> {
  public:
    typedef typename C<T>::value_type value_type;
    typedef iter_stream<T, typename C<T>::const_iterator> super;
    typedef typename super::const_iterator const_iterator;
  public:
    cont_stream(const C<T>& data) : super(), data(&data), owning(false) {}
    cont_stream(C<T>&& data) : super(), data(new C<T>(std::forward<C<T>>(data))), owning(true) {}
    virtual ~cont_stream() { if (owning && data) delete data;}
    virtual const_iterator begin() const { return data->begin(); }
    virtual const_iterator end() const { return data->end(); }
  private:
    const bool owning;
    const C<T>* data;
};

template <typename InStream, typename O, typename F>
struct map_stream_iterator {
  public:
    typedef typename InStream::value_type value_type;
    typedef value_type& reference;
    typedef value_type* pointer;
    typedef std::ptrdiff_t difference_type;
    typedef std::input_iterator_tag iterator_category;
    typedef typename InStream::const_iterator Impl;
  public:
    map_stream_iterator(Impl it, F func) : impl(it), f(func) {}

    O operator*() const {
      return f(*impl);
    }

    map_stream_iterator& operator++() {
      ++impl;
      return *this;
    }

    map_stream_iterator operator++(int) {
      map_stream_iterator tmp(*this);
      operator++();
      return tmp;
    }

    bool operator==(const map_stream_iterator& other) const {
      return impl == other.impl;
    }

    bool operator!=(const map_stream_iterator& other) const {
      return impl != other.impl;
    }

  private:
    F f;
    Impl impl;
};

template <typename O, typename I, typename InStream> 
class map_stream : public iter_stream<O, map_stream_iterator<InStream, O, std::function<O(I)> > > {
  public:
    typedef O value_type;
    typedef iter_stream<O, map_stream_iterator<InStream, O, std::function<O(I)> > > super;
    typedef typename super::const_iterator const_iterator;
  public:
    map_stream(const InStream& in, std::function<O(I)> func) : super(), in(in), f(func) {}
    virtual ~map_stream() = default;
    virtual const_iterator begin() const { return const_iterator(in.begin(), f); }
    virtual const_iterator end() const { return const_iterator(in.end(), f); }
  private:
    const InStream in;
    std::function<O(I)> f;
};

template <typename InStream>
struct filter_stream_iterator {
  public:
    typedef typename InStream::value_type value_type;
    typedef value_type& reference;
    typedef value_type* pointer;
    typedef std::ptrdiff_t difference_type;
    typedef std::input_iterator_tag iterator_category;
    typedef typename InStream::const_iterator Impl;
  public:
    filter_stream_iterator(Impl it, Impl end, std::function<bool(value_type)> predicate) : impl(it), end(end), pred(predicate) {}

    value_type operator*() const {
      return *impl;
    }

    filter_stream_iterator& operator++() {
      do {
        ++impl;
      } while (impl != end && !pred(*impl));
      return *this;
    }

    filter_stream_iterator operator++(int) {
      filter_stream_iterator tmp(*this);
      operator++();
      return tmp;
    }

    bool operator==(const filter_stream_iterator& other) const {
      return impl == other.impl;
    }

    bool operator!=(const filter_stream_iterator& other) const {
      return impl != other.impl;
    }

  private:
    std::function<bool(value_type)> pred;
    Impl impl;
    Impl end;
};

template <typename T, typename InStream> 
class filter_stream : public iter_stream<T, filter_stream_iterator<InStream>> {
  public:
    typedef T value_type;
    typedef iter_stream<T, filter_stream_iterator<InStream>> super;
    typedef typename super::const_iterator const_iterator;
  public:
    filter_stream(const InStream& in, std::function<bool(T)> predicate) : super(), in(in), pred(predicate) {}
    virtual ~filter_stream() = default;
    virtual const_iterator begin() const { return const_iterator(in.begin(), in.end(), pred); }
    virtual const_iterator end() const { return const_iterator(in.end(), in.end(), pred); }
  private:
    const InStream in;
    std::function<bool(T)> pred;
};

template <typename Cons>
struct cons_stream_iterator {
  public:
    typedef typename Cons::value_type InStream;
    typedef typename InStream::value_type value_type;
    typedef value_type& reference;
    typedef value_type* pointer;
    typedef std::ptrdiff_t difference_type;
    typedef std::input_iterator_tag iterator_category;

    typedef typename Cons::const_iterator ConsIter;
    typedef typename InStream::const_iterator StreamIter;
  public:
    cons_stream_iterator(ConsIter iter) : citer(iter) {}
    
    cons_stream_iterator& operator++() {
      if (scurr == send) {
        ++citer;
        scurr = citer->begin();
        send = citer->end();
      } else {
        ++scurr;
      }
      return *this;
    }

    cons_stream_iterator operator++(int) {
      cons_stream_iterator tmp(*this);
      operator++();
      return tmp;
    }
    
    bool operator==(const cons_stream_iterator& other) const {
      return citer == other.citer && scurr == other.scurr;
    }

    bool operator!=(const cons_stream_iterator& other) const {
      return citer != other.citer || scurr != other.scurr;
    }
  private:
    ConsIter citer;
    StreamIter scurr;
    StreamIter send;
};

template <typename T, typename InStream>
class cons_stream : public iter_stream<T, cons_stream_iterator<std::vector<InStream>>> {
  public:
    typedef T value_type;
    typedef iter_stream<T, cons_stream_iterator<std::list<InStream>>> super;
    typedef typename super::const_iterator const_iterator;
  public:
    virtual ~cons_stream() = default;
    virtual const_iterator begin() const { return const_iterator(in.begin()); }
    virtual const_iterator end() const { return const_iterator(in.end()); }
  private:
    std::list<InStream> in;
};

template <typename GenIter, typename It>
struct flatmap_stream_iterator {
  public:
    typedef typename GenIter::value_type MapStream;
    typedef typename It::value_type value_type;
    typedef value_type& reference;
    typedef value_type* pointer;
    typedef std::ptrdiff_t difference_type;
    typedef std::input_iterator_tag iterator_category;
  public:
    flatmap_stream_iterator(GenIter gen) : generator(gen) {}
    
    value_type operator*() {
      if (!mapped) {
        mapped = new MapStream(std::forward<MapStream>(*generator));
        curr = mapped->begin();
        end = mapped->end();
      }
      return *curr;
    }

    flatmap_stream_iterator& operator++() {
      ++curr;
      if (curr == end) {
        ++generator;
        delete mapped;
        mapped = nullptr;
      }
      return *this;
    }

    flatmap_stream_iterator operator++(int) {
      flatmap_stream_iterator tmp(*this);
      operator++();
      return tmp;
    }
  private:
    GenIter generator;
    MapStream* mapped = nullptr;
    It curr;
    It end;
};

template <typename O, typename I, typename InStream, typename MapStream>
class flatmap_stream : public iter_stream<O, flatmap_stream_iterator<typename InStream::const_iterator, typename MapStream::const_iterator>> {
};

template <typename T, template <class...> class C>
cont_stream<T, C> make_stream(const C<T>& data) {
  return cont_stream<T, C>(data);
}

template <typename F, typename InStream>
auto map(const InStream& stream, F func) -> map_stream<decltype(func(std::declval<typename InStream::value_type>())), typename InStream::value_type, InStream>  {
  using I = typename InStream::value_type;
  using O = decltype(func(std::declval<I>()));
  return map_stream<O, I, InStream>(stream, func);
}

template <typename P, typename InStream>
auto filter(const InStream& stream, P predicate) -> filter_stream<typename InStream::value_type, InStream> {
  using T = typename InStream::value_type;
  return filter_stream<T, InStream>(stream, predicate);
}

template <typename P, typename F, typename InStream>
auto map_if(const InStream& stream, P predicate, F func) -> decltype(map(std::declval<decltype(filter(stream, predicate))>(), func)) {
  return map(filter(stream, predicate), func);
}

//void flatMap(const InStream& stream, F func)

template <typename F, typename InStream, typename Arg1>
auto reduce(const InStream& stream, F func, Arg1 accum) -> Arg1 {
  std::for_each(stream.begin(), stream.end(), [&accum, func](typename InStream::value_type i) { accum = func(accum, i); });
  return accum;
}

}