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#lang racket (letrec ([sum-of-list (λ (l) (if (null? l) 0 (+ (car l) (sum-of-list (cdr l)))))]) (sum-of-list '(1 2 3 4 5))) ;; => 15 It is possible to write mutually recursive functions with letrec: #lang ...

A normal let form binds each value to its corresponding identifier, before executing the body. With a "named let", the body can then recursively be re-executed, passing a new value for each identifier. #lang racket (let sum-of-list ([l '(1 2 3)]) (if (null? l) 0 (+ (car ...

#lang racket (require mzlib/etc) ((rec sum-of-list (λ (l) (if (null? l) 0 (+ (car l) (sum-of-list (cdr l)))))) '(1 2 3 4 5)) ;; => 15 ;; Outside of the rec form, sum-of-list gives an error: ;; sum-of-list: undefined; ;; cannot reference an identifier befor...

It is common practice to use higher order functions instead of recursion, if there is a higher order function which expresses the right recursion pattern. In our case, sum-of-numbers can be defined using foldl: #lang racket (define (sum-of-numbers l) (foldl + 0 l)) (sum-of-numbers '(1 2 3 4 5)...

webpack 2 introduces tree shaking which can remove unused code when ES2015 modules are used to import and export code. Install npm install babel-preset-es2015-webpack --save-dev Usage in .babelrc: { "presets": [ "es2015-webpack" ] }

To update multiple documents in a collection, set the multi option to true. db.collection.update( query, update, { upsert: boolean, multi: boolean, writeConcern: document } ) multi is optional. If set to true, updates multiple documents that meet the query crit...

You have to add a div with the class .row-height inside the row, and also add .col-height to the columns. If you want to restrict the effect to a certain media query, just use the responsive .row-height and .col-height classes: for example .row-sm-height with .col-sm-height. CSS version: .row-heig...

I find that the examples in the docker inspect documentation seem magic, but do not explain much. Docker inspect is important because it is the clean way to extract information from a running container docker inspect -f ... container_id (or all running container) docker inspect -f ... $(docker p...

import numpy as np #There is a lot of math in neurons, so use numpy to speed things up in python; in other languages, use an efficient array type for that language import random #Initial neuron weights should be random class Neuron: def __init__(self, nbr_inputs, weight_array = None): ...

Since Groovy 1.8 a convenient memoize() method is added on closures: // normal closure def sum = { int x, int y -> println "sum ${x} + ${y}" return x + y } sum(3, 4) sum(3, 4) // prints // sum 3 + 4 // sum 3 + 4 // memoized closure def sumMemoize = sum.memoize() ...

Since Groovy 2.2 groovy.transform.Memoized annotation is added to convenient memoize methods with simply adding the @Memoized annotation: import groovy.transform.Memoized class Calculator { int sum(int x, int y){ println "sum ${x} + ${y}" return x+y } ...

Suppose you are searching for a Title Case pattern in a large text file and you want to edit a incorrect regular expression: First, go into Ex mode by typing q: You will now see all the commands that you typed in commandline mode, press j to go the regular expression you want to edit (/\v[A-Z]\w...

A Sample class diagram based on which we will see JPA implementation. @Entity @Table(name = "VEHICLE") @Inheritance(strategy = InheritanceType.JOINED) @DiscriminatorColumn(name = "VEHICLE_TYPE") public abstract class Vehicle { @TableGenerator(name = "VEHICLE_GE...

public ActionResult Details( string product) { .... if (productNotFound) { // http://www.eidias.com/blog/2014/7/2/mvc-custom-error-pages Response.Clear(); Response.TrySkipIisCustomErrors = true; Response.Write(product + " product not exists"); ...

Consider a one to one bidirectional relationship between employee and desk. Employee.java @Entity public class Employee { @TableGenerator(name = "employee_gen", table = "id_gen", pkColumnName = "gen_name", valueColumnName = "gen_val", allocationSize...

Show all available databases: show dbs; Select a particular database to access, e.g. mydb. This will create mydb if it does not already exist: use mydb; Show all collections in the database (be sure to select one first, see above): show collections; Show all functions that can be used w...

npm install -g rethinkdb

const r = require("rethinkdb"); r.connect({host: 'localhost', port: 28015}, (conn) => console.log(conn)) // Or as a promise let rdb_conn; r.connect({host: 'localhost', port: 28015}).then((conn) => { rdb_conn = conn; }).then(() => { // Continue to use rdb_conn }); ...

r.connect({host: 'localhost', port: 28015}) .then((conn) => { return r.dbList().run(conn); }).then((result) => { // Prints out list of databases on the RethinkDB instance console.log(result); });

r.connect({host: 'localhost', port: 28015}) .then((conn) => { return r.dbCreate("stackoverflow").run(conn); }).then((result) => { console.log(result); });