tanishiking

scala> (1 to 10000000).filter(_ % 2 == 0).take(5)
// Range(1, 2, ...., 10000000) というコレクションを展開した上で
// 全てに対して filter などの処理がが行われるためメモリに大きな負担を与え
// 最終的に必要なのは前方5つだけなのに全体をなめるので処理にかなり時間がかかる.

scala> (1 to 10000000).view.filter(_ % 2 == 0).take(5).force
res0: scala.collection.immutable.IndexedSeq[Int] = Vector(5, 10, 15, 20, 25)
// filter や take は遅延評価される
// force メソッドで正格なコレクションに戻すことができる.

tanishiking

object FibGen {

  def main(args: Array[String]): Unit = {
    fibGen.take(10).print
  }

  private[this] lazy val fibGen: Stream[Int] = 0 #:: 1 #:: fibGen.zip(fibGen.tail).map(n => n._1 + n._2)

}

tanishiking

object MyStream {

  def main(args: Array[String]): Unit = {
    range(1, 10).take(10).print
  }

  private[this] def range(start: Int, end: Int): Stream[Int] = {
    if(start >= end) {
      Stream.empty
    } else {

tanishiking

object MyGenerator {

  def main(args: Array[String]) = {
    val g = myGenerator()
    println(g()) // 1
    println(g()) // 2
    println(g()) // 3
  }

  private[this] def myGenerator(): (() => Int) = {

tanishiking

.hearty .icon-favorite:before {
  content: "\1f363";
}

.hearty .is-favorite .icon-favorite:before {
  content: "\1f37a";
}

tanishiking

<?php

function take($num, $iterable) {
    $i = 0;
    foreach($iterable as $key => $val) {
        if($i >= $num) {
            break;
        } else{
            $i++;
            yield $key => $val;

tanishiking

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from __future__ import print_function

def f(x):
    return x**3 + 2*x**2 + 10*x - 20

def df(x):
    return 3*x**2 + 4*x + 10

tanishiking

DROP TABLE IF EXISTS result;
DROP TABLE IF EXISTS student;
DROP TABLE IF EXISTS subject;

CREATE TABLE student(
    student_id INT NOT NULL,
    name       VARCHAR(256) NOT NULL,
    prefecture VARCHAR(256) NOT NULL,
    age        INT NOT NULL,
    PRIMARY KEY(student_id)

tanishiking

<?php

function fib_gen() {
    list($a, $b) = [0, 1];
    while(true) {
        yield $a;
        list($a, $b) = [$b, $a+$b];
    }
}

tanishiking

<?php

function mygenerator() {
    yield 0;
    yield 1;
    yield 2;
    yield 3;
}

$g = mygenerator();