1 /* 2 * Copyright 2014 Google Inc. All rights reserved. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef FRUIT_META_LIST_H 18 #define FRUIT_META_LIST_H 19 20 #include <fruit/impl/meta/basics.h> 21 #include <fruit/impl/meta/logical_operations.h> 22 #include <fruit/impl/meta/numeric_operations.h> 23 #include <functional> 24 25 namespace fruit { 26 namespace impl { 27 namespace meta { 28 29 // List ::= EmptyList | Cons<T, List> 30 31 struct EmptyList {}; 32 33 template <typename T, typename Tail> 34 struct Cons {}; 35 36 // TODO: Consider inlining to improve performance. 37 // If L is a list containing T1,...,Tn this calculates F(InitialValue, F(T1, F(..., F(Tn) ...))). 38 struct FoldList { 39 template <typename L, typename F, typename InitialValue> 40 struct apply; 41 42 template <typename F, typename InitialValue> 43 struct apply<EmptyList, F, InitialValue> { 44 using type = InitialValue; 45 }; 46 47 template <typename Head, typename Tail, typename F, typename InitialValue> 48 struct apply<Cons<Head, Tail>, F, InitialValue> { 49 using type = FoldList(Tail, F, F(InitialValue, Head)); 50 }; 51 }; 52 53 } // namespace meta 54 } // namespace impl 55 } // namespace fruit 56 57 #endif // FRUIT_META_LIST_H 58