Sequence

import std.algorithm;
import std.range;
import std.stdio;

alias RandomT = Random!uint;

enum sample = 5;
{ // Simple range of sequences with fixed size

    auto start = RandomT(1234);
    auto rand_range = recurrence!(q{
    a[n-1].drop(3)
    })(start);
    assert(equal(
            rand_range
            .take(sample)
            .map!q{a.take(3)}
            .joiner,
            start.save
            .take(sample * 3)));
}

{ // Range of sequences with random size
    auto start = RandomT(1234);
    // Generate sequency range with variable size in the range 4..8
    auto rand_range = recurrence!(
            (a, n) =>
            a[n - 1].progress(start.value(4, 8))
    )(Sequence!uint(start.save, 5));

    // Store the begen of the random start
    auto begin = start;
    const total_number = rand_range.take(sample).map!q{a.size}.sum;
    // restore start random
    auto expected = start = begin;
    assert(equal(expected.take(total_number),
            rand_range.take(sample).map!q{a.list}.joiner));

}