多段階選抜	解答日	シリーズ:yieldの練習/ジェネレータを入れ子に/整数平方根・立方根の実装
問題		http://nabetani.sakura.ne.jp/hena/ord24eliseq/ https://qiita.com/Nabetani/items/1c83005a854d2c6cbb69
Ruby	2014/8/2(当日)	https://qiita.com/cielavenir/items/9f15e29b73ecf98968a5
C#/Python	2014/8/4	https://qiita.com/cielavenir/items/a1156e6a4f71ddbe5dcb
		ここから上はdrop_prev_square/drop_prev_cubicをまとめる前の答案
Go/C#/Ruby/Python	2014/8/5	https://qiita.com/cielavenir/items/2a685d3080862f2c2c47
PHP/JavaScript	2014/9/9	https://qiita.com/cielavenir/items/28d613ac3823afbf8407
VB	2014/9/10	https://qiita.com/cielavenir/items/cb7266abd30eadd71c04
D	2015/12/21	https://qiita.com/cielavenir/items/47c9e50ee60bef2847ec
Perl	2017/3/10	https://qiita.com/cielavenir/items/6dfbff749d833c0fd423
Lua	2017/3/13	https://qiita.com/cielavenir/items/c60fe7e8da73487ba062
C++20(TS)	2017/3/15	https://qiita.com/cielavenir/items/e1129ca185008f49cbab (MSVC) https://qiita.com/cielavenir/items/1cfa90d73d11bb7dc3d4 (clang)
F#	2017/3/17	https://qiita.com/cielavenir/items/a698d6a26824ff53de81
Boo/Nemerle	2017/5/13	https://qiita.com/cielavenir/items/e2a783f0fe4b0fe0ed48
Perl6	2017/5/15	https://qiita.com/cielavenir/items/656ea17fa96c865c4498
Kotlin	2017/5/25	https://qiita.com/cielavenir/items/9c46ce8d9d12e51de285
Crystal	2018/5/8	https://qiita.com/cielavenir/items/1815bfa6a860fd1f90db
MoonScript	2018/6/16	https://qiita.com/cielavenir/items/8b03cce0386f4537b5ad
Julia/Rust	2018/12/20	https://qiita.com/cielavenir/items/3ddf72b06d625da0c4a5
Nim	2018/12/26	https://qiita.com/cielavenir/items/5728944867e609fd52a7
Tcl	2018/12/31	https://qiita.com/cielavenir/items/76cbd9c2022b48c9a2c9
Pascal/Cobra	2019/1/16	https://qiita.com/cielavenir/items/81b81baf8dfc1f877903
Icon	2019/1/17	https://qiita.com/cielavenir/items/889622dcc721f5a4da24
Swift	2020/5/31	https://qiita.com/cielavenir/items/3b0b84a218e35d538f7f
Java/Groovy/Scala	2020/5/31	https://qiita.com/cielavenir/items/7f058203a8fd03b65870
V	2020/10/17	https://qiita.com/cielavenir/items/df30a6c101a97a713df5
Zig/Zen	2020/10/17	https://qiita.com/cielavenir/items/9cced9e4a94dcd70df0f
Pike	2020/11/2	https://qiita.com/cielavenir/items/3a8248f41611302b34fd
Vala/Smalltalk	2020/11/29	https://qiita.com/cielavenir/items/085dabe593cd916af5e8
Objective-C	2020/11/30	https://qiita.com/cielavenir/items/a1736e38789a3dd5cc5a
Ruby(Ractor)	2021/1/2	https://qiita.com/cielavenir/items/f493c6d512b63cc571cc
Python(_xxsubinterpreters)	2021/6/29	https://qiita.com/cielavenir/items/f1f581a055db918954f1
Falcon/Scheme	2021/9/5	https://qiita.com/cielavenir/items/c13d12cf44f0d17f4a94
Clojure/Lisp	2021/9/7	https://qiita.com/cielavenir/items/7458ba076f4e5bc0f196
(icbrtの実装に関する)補題	2017/5/11	整数除算であってもn/(x*y)はn/x/yに等しい(ことの証明) https://qiita.com/cielavenir/items/21a6711afd6be8c18c55

2015/03/24にリリースされたD 2.067でGeneratorが追加されたことを知った(遅すぎ)。(Javaとは違って)ありがたいことにyieldが実装されている。
yieldといえば、多段階選抜である。

それにしても、reduceが効かなかったのは少し残念。

ところで、f['2']とかの宣言があれなのは、ラムダ式キャプチャの都合。Pythonもこういう性質を持つらしい。

tyama_hena24_enum.d

#!/usr/bin/env rdmd
// http://qiita.com/Nabetani/items/1c83005a854d2c6cbb69
// http://nabetani.sakura.ne.jp/hena/ord24eliseq/

import std.stdio,std.string,std.math;
import std.algorithm,std.concurrency;

int isqrt(int n){
    if(n<=0)return 0;
    if(n<4)return 1;
    int x=0,y=n;
    for(;x!=y&&x+1!=y;)x=y,y=(n/y+y)/2;
    return x;
}
int icbrt(int n){
    if(n<0)return -icbrt(-n);
    if(n==0)return 0;
    if(n<8)return 1;
    int x=0,y=n;
    for(;x!=y&&x+1!=y;)x=y,y=(n/y/y+y*2)/3;
    return x;
}

auto generate(){
    return new Generator!int({
        int i=1;
        for(;;){
            yield(i);
            i+=1;
        }
    });
}
auto drop_prev(bool delegate(int) check,Generator!int prev){
    return new Generator!int({
        int a=prev.front;
        prev.popFront();
        int b=prev.front;
        for(;;){
            if(!check(b))yield(a);
            a=b;
            prev.popFront();
            b=prev.front;
        }
    });
}
auto drop_next(bool delegate(int) check,Generator!int prev){
    return new Generator!int({
        int a=prev.front;
        prev.popFront();
        int b=prev.front;
        yield(a);
        for(;;){
            if(!check(a))yield(b);
            a=b;
            prev.popFront();
            b=prev.front;
        }
    });
}
auto drop_n(bool delegate(int,int) check,int n,Generator!int prev){
    return new Generator!int({
        int i=0;
        for(;;){
            i++;
            int a=prev.front;
            if(!check(i,n))yield(a);
            prev.popFront();
        }
    });
}

void main(){
    bool is_sq(int n){
        //int x=cast(int)sqrt(cast(real)n);
        int x=isqrt(n);
        return x*x==n;
    }
    bool is_cb(int n){
        //int x=cast(int)cbrt(cast(real)n);
        int x=icbrt(n);
        return x*x*x==n;
    }
    bool is_multiple(int i,int n){return i%n==0;}
    bool is_le(int i,int n){return i<=n;}

    Generator!int delegate(Generator!int)[char] f=[
        'S':e => drop_next(&is_sq,e),
        's':e => drop_prev(&is_sq,e),
        'C':e => drop_next(&is_cb,e),
        'c':e => drop_prev(&is_cb,e),
        'h':e => drop_n(&is_le,100,e),
    ];
    for(int i=2;i<10;i++){
        f[cast(char)('0'+i)] = delegate(int i){return (Generator!int e)=>drop_n(&is_multiple,i,e);}(i);
    }
    string line;
    for(;(line=stdin.readln()) !is null;){
        line=chomp(line);
        bool first=true;
        //cS => f['S'](f['c'](generate()))
        //auto z=reduce!((s,e)=>f[e](s))(generate(),line);

        auto z=generate();
        foreach(char e;line)z=f[e](z);

        for(int i=0;i<10;i++){
            int n=z.front;
            z.popFront();
            if(!first)write(',');
            first=false;
            write(n);
        }
        writeln();
        stdout.flush();
    }
}