LeechCraft  0.6.70-10870-g558588d6ec
Modular cross-platform feature rich live environment.
monad.h
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29 
30 #pragma once
31 
32 #include <boost/optional.hpp>
33 #include "typelist.h"
34 #include "applicative.h"
35 
36 namespace LeechCraft
37 {
38 namespace Util
39 {
40  template<typename T>
41  struct InstanceMonad;
42 
43  template<template<typename...> class Monad, typename... Args, typename V>
44  auto Return (const V& v)
45  {
46  return Pure<Monad, Args...> (v);
47  }
48 
49  template<typename MV, typename F>
51 
52  namespace detail
53  {
54  template<template<typename...> class Monad, typename... Args1, typename... Args2>
55  constexpr bool IsCompatibleMonadImpl (const Monad<Args1...>*, const Monad<Args2...>*, int)
56  {
57  return std::is_same<
58  decltype (Init (Typelist<Args1...> {})),
59  decltype (Init (Typelist<Args2...> {}))
60  >::value;
61  }
62 
63  template<typename T1, typename T2>
64  constexpr bool IsCompatibleMonadImpl (const T1*, const T2*, ...)
65  {
66  return false;
67  }
68 
69  template<typename T>
70  constexpr T* declptr () noexcept
71  {
72  return nullptr;
73  }
74 
75  template<typename T1, typename T2>
76  constexpr bool IsCompatibleMonad ()
77  {
78  return IsCompatibleMonadImpl (detail::declptr<T1> (), detail::declptr<T2> (), 0);
79  }
80  }
81 
82  template<typename MV, typename F>
83  BindResult_t<MV, F> Bind (const MV& value, const F& f)
84  {
85  static_assert (detail::IsCompatibleMonad<MV, BindResult_t<MV, F>> (),
86  "Incompatible function return type");
87  return InstanceMonad<MV>::Bind (value, f);
88  }
89 
90  template<typename MV, typename F>
91  auto operator>> (const MV& value, const F& f) -> decltype (Bind (value, f))
92  {
93  return Bind (value, f);
94  }
95 
96  template<typename MV>
97  auto Do (const MV& value)
98  {
99  return value;
100  }
101 
102  template<typename MV, typename FHead, typename... FArgs>
103  auto Do (const MV& value, const FHead& fHead, const FArgs&... fArgs)
104  {
105  return Do (Bind (value, fHead), fArgs...);
106  }
107 
108  // Implementations
109  template<typename T>
110  struct InstanceMonad<boost::optional<T>>
111  {
112  template<typename F>
113  using BindResult_t = std::result_of_t<F (T)>;
114 
115  template<typename F>
116  static BindResult_t<F> Bind (const boost::optional<T>& value, const F& f)
117  {
118  if (!value)
119  return {};
120 
121  return f (*value);
122  }
123  };
124 }
125 }
constexpr detail::ExprTree< detail::ExprType::LeafStaticPlaceholder, detail::MemberPtrs< Ptr > > f
Definition: oral.h:931
auto operator>>(const MV &value, const F &f) -> decltype(Bind(value, f))
Definition: monad.h:91
Definition: prelude.h:39
static BindResult_t< F > Bind(const boost::optional< T > &value, const F &f)
Definition: monad.h:116
auto Return(const V &v)
Definition: monad.h:44
auto Pure(const T &v)
Definition: applicative.h:45
constexpr bool IsCompatibleMonad()
Definition: monad.h:76
constexpr bool IsCompatibleMonadImpl(const Monad< Args1... > *, const Monad< Args2... > *, int)
Definition: monad.h:55
typename InstanceMonad< MV >::template BindResult_t< F > BindResult_t
Definition: monad.h:50
auto Do(const MV &value)
Definition: monad.h:97
constexpr T * declptr() noexcept
Definition: monad.h:70
BindResult_t< MV, F > Bind(const MV &value, const F &f)
Definition: monad.h:83