Tutorial by Examples: r

To export the type and all its constructors, one must use the following syntax: module X (Person (..)) where So, for the following top-level definitions in a file called People.hs: data Person = Friend String | Foe deriving (Show, Eq, Ord) isFoe Foe = True isFoe _ = False This module d...

Haskell supports importing a subset of items from a module. import qualified Data.Stream (map) as D would only import map from Data.Stream, and calls to this function would require D.: D.map odd [1..] otherwise the compiler will try to use Prelude's map function.

Prelude often defines functions whose names are used elsewhere. Not hiding such imports (or using qualified imports where clashes occur) will cause compilation errors. Data.Stream defines functions named map, head and tail which normally clashes with those defined in Prelude. We can hide those impo...

When multiple modules define the same functions by name, the compiler will complain. In such cases (or to improve readability), we can use a qualified import: import qualified Data.Stream as D Now we can prevent ambiguity compiler errors when we use map, which is defined in Prelude and Data.Stre...

C99 Macros with variadic args: Let's say you want to create some print-macro for debugging your code, let's take this macro as an example: #define debug_print(msg) printf("%s:%d %s", __FILE__, __LINE__, msg) Some examples of usage: The function somefunc() returns -1 if failed and 0 ...

Convert in uppercase the string argument Syntax: UPPER(str) UPPER('fOoBar') -- 'FOOBAR' UCASE('fOoBar') -- 'FOOBAR'

To concatenate the value of two or more variables into a single string and print it as the output, we need to make use of interpolation. The following Less code, #demo:after { @var1: Hello; @var2: World!!!; content: "@{var1} @{var2}"; } when compiled would set "Hello Wo...

Drawing to canvas isn't just limited to shapes and images. You can also draw text to the canvas. To draw text on the canvas, get a reference to the canvas and then call the fillText method on the context. var canvas = document.getElementById('canvas'); var ctx = canvas.getContext('2d'); ctx.fill...

The default font formatting provided by the fillText and strokeText methods isn't very aesthetically appealing. Fortunately the canvas API provides properties for formatting text. Using the font property you can specify: font-style font-variant font-weight font-size / line-height font-family...

Native Canvas API does not have a method to wrap text onto the next line when a desired maximum width is reached. This example wraps text into paragraphs. function wrapText(text, x, y, maxWidth, fontSize, fontFace){ var firstY=y; var words = text.split(' '); var line = ''; var lineHeigh...

This example draws text paragraphs into any portions of the canvas that have opaque pixels. It works by finding the next block of opaque pixels that is large enough to contain the next specified word and filling that block with the specified word. The opaque pixels can come from any source: Path d...

Classes, structs, enums and all their methods are internal by default. This means they can be only accessed from the same module. The test cases are in a different target an this means they are in a different module. To be able to access the method you want to test, you need to import the module to ...

If you want to add a Drawable be shown during the load, you can add a placeholder: Glide.with(context) .load(yourUrl) .placeholder(R.drawable.placeholder) .into(imageView); If you want a Drawable to be shown if the load fails for any reason: Glide.with(context) .load(yourUrl...

View loading In a test for a view controller you want sometimes to trigger the execution of loadView() or viewDidLoad(). This can be done by accessing the view. Let's say you have view controller instance in your test called sut (system under test), then the code would look like this: XCTAssertNot...

Some attributes are directly accessible as properties of the element (e.g. alt, href, id, title and value). document.querySelector("a").href = "#top"; Other attributes, including data-attributes can be set as follows: document.querySelector("a").setAttribute("...

To remove an attribute, including directly accessible properties document.querySelector("a").removeAttribute("title"); Data attributes can also be removed as follows (modern browsers): // remove "data-foo" attribute delete document.querySelector("a").dat...

// Add observer let observer = NSNotificationCenter.defaultCenter().addObserverForName("nameOfTheNotification", object: nil, queue: nil) { (notification) in // Do operations with the notification in this block } // Remove observer NSNotificationCenter.defaultCenter().removeObser...

4.0 Since bash 4.0, a new operator ;& was introduced which provides fall through mechanism. #!/bin/bash var=1 case $var in 1) echo "Antartica" ;& 2) echo "Brazil" ;& 3) echo "Cat" ;& esac Outputs: Antartica Brazil Cat ...

4.0 Since Bash 4.0, another operator ;;& was introduced which also provides fall through only if the patterns in subsequent case statement(s), if any, match. #!/bin/bash var=abc case $var in a*) echo "Antartica" ;;& xyz) echo "Brazil" ;;& *b*) ...

Quintile analysis is a common framework for evaluating the efficacy of security factors. What is a factor A factor is a method for scoring/ranking sets of securities. For a particular point in time and for a particular set of securities, a factor can be represented as a pandas series where the in...