mcs/tests/gtest-iter-06.cs

   1 using System;
   2 using System.Collections.Generic;
   3
   4 namespace Mono.Rocks
   5 {
   6         public static class KeyValuePair
   7         {
   8                 public static KeyValuePair<TKey, TValue>? Just<TKey, TValue> (TKey key, TValue value)
   9                 {
  10                         return new KeyValuePair<TKey, TValue> (key, value);
  11                 }
  12         }
  13
  14         public static class Sequence
  15         {
  16                 public static IEnumerable<TResult> Unfoldr<TSource, TResult> (TSource value, Func<TSource, KeyValuePair<TResult, TSource>?> func)
  17                 {
  18                         return CreateUnfoldrIterator (value, func);
  19                 }
  20
  21                 private static IEnumerable<TResult> CreateUnfoldrIterator<TSource, TResult> (TSource value, Func<TSource, KeyValuePair<TResult, TSource>?> func)
  22                 {
  23                         KeyValuePair<TResult, TSource>? r;
  24                         while ((r = func (value)).HasValue) {
  25                                 KeyValuePair<TResult, TSource> v = r ?? new KeyValuePair<TResult, TSource> ();
  26                                 yield return v.Key;
  27                                 value = v.Value;
  28                         }
  29                 }
  30         }
  31
  32         class Test
  33         {
  34                 public static int Main ()
  35                 {
  36                         IEnumerable<int> x = Sequence.Unfoldr (10, b => b == 0
  37                                 ? null
  38                                 : KeyValuePair.Just (b, b - 1));
  39
  40                         int i = 10;
  41                         foreach (int e in x) {
  42                                 Console.WriteLine (e);
  43                                 if (i-- != e)
  44                                         return 1;
  45                         }
  46
  47                         return 0;
  48                 }
  49         }
  50 }