LeechCraft  0.6.70-13729-g7046a9d2a7
Modular cross-platform feature rich live environment.
monad.h
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29 
30 #pragma once
31 
32 #include <optional>
33 #include <boost/optional.hpp>
34 #include "typelist.h"
35 #include "applicative.h"
36 
37 namespace LC
38 {
39 namespace Util
40 {
41  template<typename T>
42  struct InstanceMonad;
43 
44  template<template<typename...> class Monad, typename... Args, typename V>
45  auto Return (const V& v)
46  {
47  return Pure<Monad, Args...> (v);
48  }
49 
50  template<typename MV, typename F>
52 
53  namespace detail
54  {
55  template<template<typename...> class Monad, typename... Args1, typename... Args2>
56  constexpr bool IsCompatibleMonadImpl (const Monad<Args1...>*, const Monad<Args2...>*, int)
57  {
58  return std::is_same<
59  decltype (Init (Typelist<Args1...> {})),
60  decltype (Init (Typelist<Args2...> {}))
61  >::value;
62  }
63 
64  template<typename T1, typename T2>
65  constexpr bool IsCompatibleMonadImpl (const T1*, const T2*, ...)
66  {
67  return false;
68  }
69 
70  template<typename T>
71  constexpr T* declptr () noexcept
72  {
73  return nullptr;
74  }
75 
76  template<typename T1, typename T2>
77  constexpr bool IsCompatibleMonad ()
78  {
79  return IsCompatibleMonadImpl (detail::declptr<T1> (), detail::declptr<T2> (), 0);
80  }
81  }
82 
83  template<typename MV, typename F>
84  BindResult_t<MV, F> Bind (const MV& value, const F& f)
85  {
86  static_assert (detail::IsCompatibleMonad<MV, BindResult_t<MV, F>> (),
87  "Incompatible function return type");
88  return InstanceMonad<MV>::Bind (value, f);
89  }
90 
91  template<typename MV, typename F>
92  auto operator>> (const MV& value, const F& f) -> decltype (Bind (value, f))
93  {
94  return Bind (value, f);
95  }
96 
97  template<typename MV>
98  auto Do (const MV& value)
99  {
100  return value;
101  }
102 
103  template<typename MV, typename FHead, typename... FArgs>
104  auto Do (const MV& value, const FHead& fHead, const FArgs&... fArgs)
105  {
106  return Do (Bind (value, fHead), fArgs...);
107  }
108 
109  // Implementations
110  template<typename T>
111  struct InstanceMonad<boost::optional<T>>
112  {
113  template<typename F>
114  using BindResult_t = std::result_of_t<F (T)>;
115 
116  template<typename F>
117  static BindResult_t<F> Bind (const boost::optional<T>& value, const F& f)
118  {
119  if (!value)
120  return {};
121 
122  return f (*value);
123  }
124  };
125 
126  template<typename T>
127  struct InstanceMonad<std::optional<T>>
128  {
129  template<typename F>
130  using BindResult_t = std::result_of_t<F (T)>;
131 
132  template<typename F>
133  static BindResult_t<F> Bind (const std::optional<T>& value, const F& f)
134  {
135  if (!value)
136  return {};
137 
138  return f (*value);
139  }
140  };
141 }
142 }
BindResult_t< MV, F > Bind(const MV &value, const F &f)
Definition: monad.h:84
Definition: prelude.h:38
static BindResult_t< F > Bind(const boost::optional< T > &value, const F &f)
Definition: monad.h:117
auto operator>>(const MV &value, const F &f) -> decltype(Bind(value, f))
Definition: monad.h:92
STL namespace.
auto Pure(const T &v)
Definition: applicative.h:46
typename InstanceMonad< MV >::template BindResult_t< F > BindResult_t
Definition: monad.h:51
std::result_of_t< F(T)> BindResult_t
Definition: monad.h:114
constexpr detail::ExprTree< detail::ExprType::LeafStaticPlaceholder, detail::MemberPtrs< Ptr > > f
Definition: oral.h:955
std::result_of_t< F(T)> BindResult_t
Definition: monad.h:130
auto Do(const MV &value)
Definition: monad.h:98
constexpr T * declptr() noexcept
Definition: monad.h:71
static BindResult_t< F > Bind(const std::optional< T > &value, const F &f)
Definition: monad.h:133
constexpr bool IsCompatibleMonadImpl(const Monad< Args1... > *, const Monad< Args2... > *, int)
Definition: monad.h:56
constexpr bool IsCompatibleMonad()
Definition: monad.h:77
auto Return(const V &v)
Definition: monad.h:45
Definition: constants.h:35