Tutorial by Examples: f

first and second

If mapping covariantly over only the first argument, or only the second argument, is desired, then first or second ought to be used (in lieu of bimap). first :: Bifunctor f => (a -> c) -> f a b -> f c b first f = bimap f id second :: Bifunctor f => (b -> d) -> f a b -> f...

Basic Example of Html 5 cache

this is our index.html file <!DOCTYPE html> <html manifest="index.appcache"> <body> <p>Content</p> </body> </html> then we will create index.appcache file with below codes CACHE MANIFEST index.html write those files that you want ...

Definition of Bifunctor

Bifunctor is the class of types with two type parameters (f :: * -> * -> *), both of which can be covariantly mapped over simultaneously. class Bifunctor f where bimap :: (a -> c) -> (b -> d) -> f a b -> f c d bimap can be thought of as applying a pair of fmap operation...

Polynomial functors

There's a useful set of type combinators for building big Functors out of smaller ones. These are instructive as example instances of Functor, and they're also useful as a technique for generic programming, because they can be used to represent a large class of common functors. The identity functor...

Sample illustration using ASP.Net Web Forms

GridView definition on ASPX page As shown below, first column of grid is defined as a checkbox column, which is conditionally cleared as shown in further examples below (the header checkbox is only for selecting/un-selecting all rows on current page, but same can be extended for all on grid easily)...

Default values of uninitialized variables

Although not necessary in PHP however it is a very good practice to initialize variables. Uninitialized variables have a default value of their type depending on the context in which they are used: Unset AND unreferenced var_dump($unset_var); // outputs NULL Boolean echo($unset_bool ? "tr...

Fluent Wait

Fluent wait is a superclass of explicit wait (WebDriverWait) that is more configurable since it can accept an argument to the wait function. I'll pass on implicit wait, since it's a best practice to avoid it. Usage (Java): Wait wait = new FluentWait<>(this.driver) .withTimeout(drive...

Use your favorite tool shortcuts in Android Studio

Go to File > Settings > Keymap and select the Keymaps option from: Mac OS X Emacs Visual Studio Eclise Netbeans Jbuilder and others, to map the shortcuts to the wanted tool ones.

Using instanceof

instanceof requires that the variable is of type any. This code (try it): class Pet { } class Dog extends Pet { bark() { console.log("woof"); } } class Cat extends Pet { purr() { console.log("meow"); } } function example(foo: any) { ...

Using typeof

typeof is used when you need to distinguish between types number, string, boolean, and symbol. Other string constants will not error, but won't be used to narrow types either. Unlike instanceof, typeof will work with a variable of any type. In the example below, foo could be typed as number | str...

Type guarding functions

You can declare functions that serve as type guards using any logic you'd like. They take the form: function functionName(variableName: any): variableName is DesiredType { // body that returns boolean } If the function returns true, TypeScript will narrow the type to DesiredType in any bl...

ssh_exchange_identification: read: Connection reset by peer

This error message may be produced by the OpenSSH ssh client. It means that the TCP connection between the client and the server was abnormally closed by the server immediately after being accepted. Common reasons for this message include: The SSH server process is malfunctioning--for example, it...

ssh_exchange_identification: Connection closed by remote host

This error message may be produced by the OpenSSH ssh client. It means that the TCP connection between the client and the server was closed by the server immediately after being accepted. This message generally indicates the SSH server has been configured not to accept connections from the client fo...

Date Difference Calculation

To compare the difference of two dates, we can do the comparison based on the timestamp. var date1 = new Date(); var date2 = new Date(date1.valueOf() + 5000); var dateDiff = date1.valueOf() - date2.valueOf(); var dateDiffInYears = dateDiff/1000/60/60/24/365; //convert milliseconds into years ...

Functors in Category Theory

A Functor is defined in category theory as a structure-preserving map (a 'homomorphism') between categories. Specifically, (all) objects are mapped to objects, and (all) arrows are mapped to arrows, such that the category laws are preserved. The category in which objects are Haskell types and morph...

Finding Spotify's documentation

Spotify currently hosts documentation for all its third-party developer tools on its Developer Site.

Using a predefined ruleset as default

tslint can extend an existing rule set and is shipped with the defaults tslint:recommended and tslint:latest. tslint:recommended is a stable, somewhat opinionated set of rules which we encourage for general TypeScript programming. This configuration follows semver, so it will not have breaking ch...

The Freer monad

There's an alternative formulation of the free monad called the Freer (or Prompt, or Operational) monad. The Freer monad doesn't require a Functor instance for its underlying instruction set, and it has a more recognisably list-like structure than the standard free monad. The Freer monad represents...

Mounting a remote NFS drive

mount { '/path/to/local/folder': ensure => 'mounted', atboot => false, device => 'server-ip-or-domain:/path/to/server/folder', fstype => 'nfs', options => 'defaults', pass => 0, }

Load and Filter Data

# imports import weka.core.converters.ConverterUtils.DataSource as DS import weka.filters.Filter as Filter import weka.filters.unsupervised.attribute.Remove as Remove import os # load data data = DS.read(os.environ.get("MOOC_DATA") + os.sep + "iris.arff") # remove clas...

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