lazy.cpp
11.8 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
// Copyright Louis Dionne 2013-2022
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
#include <boost/hana/lazy.hpp>
#include <boost/hana/ap.hpp>
#include <boost/hana/assert.hpp>
#include <boost/hana/chain.hpp>
#include <boost/hana/concept/comparable.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/duplicate.hpp>
#include <boost/hana/equal.hpp>
#include <boost/hana/eval.hpp>
#include <boost/hana/extend.hpp>
#include <boost/hana/extract.hpp>
#include <boost/hana/flatten.hpp>
#include <boost/hana/functional/compose.hpp>
#include <boost/hana/lift.hpp>
#include <boost/hana/transform.hpp>
#include <boost/hana/tuple.hpp>
#include <laws/applicative.hpp>
#include <laws/base.hpp>
#include <laws/comonad.hpp>
#include <laws/functor.hpp>
#include <laws/monad.hpp>
#include <support/tracked.hpp>
#include <array>
#include <iostream>
namespace hana = boost::hana;
using hana::test::ct_eq;
namespace boost { namespace hana {
// We provide this instance for unit tests only because it is _so_ much
// more convenient, but this instance is too dangerous for general usage.
// See the documentation of `hana::lazy` for more info.
template <>
struct equal_impl<lazy_tag, lazy_tag> {
template <typename X, typename Y>
static constexpr auto apply(X x, Y y)
{ return hana::equal(hana::eval(x), hana::eval(y)); }
};
}}
auto invalid = [](auto x)
{ return x.this_function_must_not_be_instantiated; };
int main() {
hana::test::_injection<0> f{};
auto eqs = hana::make_tuple(
hana::make_lazy(ct_eq<0>{}),
hana::make_lazy(ct_eq<1>{}),
hana::make_lazy(ct_eq<2>{})
);
auto eq_elems = hana::make_tuple(ct_eq<0>{}, ct_eq<1>{}, ct_eq<1>{});
auto nested = hana::make_tuple(
hana::make_lazy(hana::make_lazy(ct_eq<0>{})),
hana::make_lazy(hana::make_lazy(ct_eq<1>{})),
hana::make_lazy(hana::make_lazy(ct_eq<2>{}))
);
//////////////////////////////////////////////////////////////////////////
// Lazy methods
//////////////////////////////////////////////////////////////////////////
{
// lazy
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::make_lazy(f)(),
hana::make_lazy(f())
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::make_lazy(f)(ct_eq<0>{}),
hana::make_lazy(f(ct_eq<0>{}))
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::make_lazy(f)(ct_eq<0>{}, ct_eq<1>{}),
hana::make_lazy(f(ct_eq<0>{}, ct_eq<1>{}))
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::make_lazy(f)(ct_eq<0>{}, ct_eq<1>{}, ct_eq<2>{}),
hana::make_lazy(f(ct_eq<0>{}, ct_eq<1>{}, ct_eq<2>{}))
));
// The function is not applied.
hana::make_lazy(invalid)();
hana::make_lazy(invalid)(ct_eq<0>{});
hana::make_lazy(invalid)(ct_eq<0>{}, ct_eq<1>{});
hana::make_lazy(invalid)(ct_eq<0>{}, ct_eq<1>{}, ct_eq<2>{});
}
// eval
{
// With lazy expressions
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval(hana::make_lazy(ct_eq<0>{})),
ct_eq<0>{}
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval(hana::make_lazy(ct_eq<1>{})),
ct_eq<1>{}
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval(hana::make_lazy(f)()),
f()
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval(hana::make_lazy(f)(ct_eq<3>{})),
f(ct_eq<3>{})
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval(hana::make_lazy(f)(ct_eq<3>{}, ct_eq<4>{})),
f(ct_eq<3>{}, ct_eq<4>{})
));
// Should call a nullary function
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval([]{ return ct_eq<3>{}; }),
ct_eq<3>{}
));
// Should call a unary function with hana::id.
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval([](auto _) { return _(ct_eq<3>{}); }),
ct_eq<3>{}
));
// For overloaded function objects that are both nullary and unary,
// the nullary overload should be preferred.
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::eval(f),
f()
));
}
// Make sure this does not move from a destroyed object, as that
// used to be the case.
{
auto x = hana::flatten(hana::make_lazy(hana::make_lazy(Tracked{1})));
auto z = hana::eval(x); (void)z;
}
// In some cases where a type has a constructor that is way too
// general, copying a lazy value holding an object of that type
// could trigger the instantiation of that constructor. If that
// constructor was ill-formed, the compilation would fail. We
// make sure this does not happen.
{
{
auto expr = hana::make_lazy(hana::test::trap_construct{});
auto implicit_copy = expr; (void)implicit_copy;
decltype(expr) explicit_copy(expr); (void)explicit_copy;
}
{
auto expr = hana::make_lazy(hana::test::trap_construct{})();
auto implicit_copy = expr; (void)implicit_copy;
decltype(expr) explicit_copy(expr); (void)explicit_copy;
}
}
}
//////////////////////////////////////////////////////////////////////////
// Functor
//////////////////////////////////////////////////////////////////////////
{
// transform
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::transform(hana::make_lazy(ct_eq<0>{}), f),
hana::make_lazy(f(ct_eq<0>{}))
));
}
// laws
hana::test::TestFunctor<hana::lazy_tag>{eqs, eq_elems};
}
//////////////////////////////////////////////////////////////////////////
// Applicative
//////////////////////////////////////////////////////////////////////////
{
// ap
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::ap(hana::make_lazy(f), hana::make_lazy(ct_eq<0>{})),
hana::make_lazy(f(ct_eq<0>{}))
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::ap(hana::make_lazy(f), hana::make_lazy(ct_eq<0>{}), hana::make_lazy(ct_eq<1>{})),
hana::make_lazy(f(ct_eq<0>{}, ct_eq<1>{}))
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::ap(hana::make_lazy(f), hana::make_lazy(ct_eq<0>{}), hana::make_lazy(ct_eq<1>{}), hana::make_lazy(ct_eq<2>{})),
hana::make_lazy(f(ct_eq<0>{}, ct_eq<1>{}, ct_eq<2>{}))
));
// The function is not applied.
hana::ap(hana::make_lazy(invalid), hana::make_lazy(ct_eq<0>{}));
hana::ap(hana::make_lazy(invalid), hana::make_lazy(ct_eq<0>{}), hana::make_lazy(ct_eq<1>{}));
hana::ap(hana::make_lazy(invalid), hana::make_lazy(ct_eq<0>{}), hana::make_lazy(ct_eq<1>{}), hana::make_lazy(ct_eq<2>{}));
}
// lift
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::lift<hana::lazy_tag>(ct_eq<0>{}),
hana::make_lazy(ct_eq<0>{})
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::lift<hana::lazy_tag>(ct_eq<1>{}),
hana::make_lazy(ct_eq<1>{})
));
}
// laws
hana::test::TestApplicative<hana::lazy_tag>{eqs};
}
//////////////////////////////////////////////////////////////////////////
// Monad
//////////////////////////////////////////////////////////////////////////
{
auto f_ = hana::compose(hana::make_lazy, f);
// chain
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::chain(hana::make_lazy(ct_eq<0>{}), f_),
f_(ct_eq<0>{})
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::chain(hana::make_lazy(ct_eq<1>{}), f_),
f_(ct_eq<1>{})
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::make_lazy(ct_eq<1>{}) | f_,
f_(ct_eq<1>{})
));
}
// flatten
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::flatten(hana::make_lazy(hana::make_lazy(ct_eq<0>{}))),
hana::make_lazy(ct_eq<0>{})
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::flatten(hana::make_lazy(hana::make_lazy(ct_eq<1>{}))),
hana::make_lazy(ct_eq<1>{})
));
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::flatten(hana::make_lazy(hana::make_lazy(hana::make_lazy(ct_eq<1>{})))),
hana::make_lazy(hana::make_lazy(ct_eq<1>{}))
));
}
// laws
hana::test::TestMonad<hana::lazy_tag>{eqs, nested};
}
//////////////////////////////////////////////////////////////////////////
// Comonad
//////////////////////////////////////////////////////////////////////////
{
// extract
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::extract(hana::make_lazy(ct_eq<4>{})),
ct_eq<4>{}
));
}
// duplicate
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::duplicate(hana::make_lazy(ct_eq<4>{})),
hana::make_lazy(hana::make_lazy(ct_eq<4>{}))
));
}
// extend
{
BOOST_HANA_CONSTANT_CHECK(hana::equal(
hana::extend(hana::make_lazy(ct_eq<4>{}), f),
hana::make_lazy(f(hana::make_lazy(ct_eq<4>{})))
));
}
// laws
hana::test::TestComonad<hana::lazy_tag>{eqs};
}
//////////////////////////////////////////////////////////////////////////
// Make sure the monadic chain is evaluated in the right order.
//////////////////////////////////////////////////////////////////////////
{
std::array<bool, 3> executed = {{false, false, false}};
int dummy = 0;
std::cout << "creating the monadic chain...\n";
auto chain = hana::make_lazy(dummy)
| [&](int dummy) {
std::cout << "executing the first computation...\n";
executed[0] = true;
BOOST_HANA_RUNTIME_CHECK(
executed == std::array<bool, 3>{{true, false, false}}
);
return hana::make_lazy(dummy);
}
| [&](int dummy) {
std::cout << "executing the second computation...\n";
executed[1] = true;
BOOST_HANA_RUNTIME_CHECK(
executed == std::array<bool, 3>{{true, true, false}}
);
return hana::make_lazy(dummy);
}
| [&](int dummy) {
std::cout << "executing the third computation...\n";
executed[2] = true;
BOOST_HANA_RUNTIME_CHECK(
executed == std::array<bool, 3>{{true, true, true}}
);
return hana::make_lazy(dummy);
};
BOOST_HANA_RUNTIME_CHECK(
executed == std::array<bool, 3>{{false, false, false}}
);
std::cout << "evaluating the chain...\n";
hana::eval(chain);
}
}