Mental Workbench

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====== F# workshop ======
{{:projects:fsharp_logo.png?nolink|}}
===== Prerequisites =====
    * https://www.linqpad.net/ or anything that can execute a REPL((Read, Evaluate, Print Loop))
<hidden ↘ alternatives>
    * Try F# in browser: http://www.tryfsharp.org/Create
    * Use Visual Studio https://www.visualstudio.com/
    * Get a full distribution: http://fsharp.org/use/windows/ OR http://fsharp.org/use/linux/
</hidden>

===== Agenda =====

  * hello(x)
  * Type providers (strongly typed)
  * Matching
  * Options


===== hello(x) =====
<code fsharp>
let hello = printf "Hello World"
hello
</code>

F# (pronounced “F Sharp”) is 

<WRAP group>
<WRAP half column box>
  * Open Source
  * Multi platform
  * Modern, rising popularity
  * Lazy evaluated
  * Reusable
  * Concise (See [[http://theburningmonk.com/2014/12/seven-ineffective-coding-habits-many-f-programmers-dont-have/|signal-to-noise ratio]])
  * Strongly typed
  * Functional first
    * Use functional to write easy to test and understand code
    * Use imperative for performance and compatibility
    * Use objective for organization and encapsulation
  * Compiled
</WRAP>

<WRAP half column box>
  * Not suitable for real time (unpredictable performance)
  * Hard to optimize (Functional languages fundamentally don't model how your computer works)
  * Functional first (different thinking process, you will need to re-learn)
</WRAP>
</WRAP>
programming language for writing simple code to solve complex problems. 

<code fsharp>
let hello x = printfn "Hello %s" x
hello "world"
</code>

Introducing pipeline operator:
<code fsharp>
let hello x = printfn "Hello %s" x
"World" |> hello
</code>

<hidden pipeline operator definition>
How to define the operator? 
<code fsharp>
let inline (|>) x f = f x
</code>
</hidden>

<code fsharp>
let square x = x * x
let subtract x y = x - y
</code>

<code fsharp>
let ``complicated stuff`` x =
    printfn "%d" (add 5 (square x))
</code>

<code fsharp>
let ``another complicated stuff`` x =
    x |> square |> subtract 5 |> printfn "%d"
</code>

<code fsharp>
let equation x =
	x 
	|> (fun y -> y * y ) 
	|> (fun y z -> y - z ) 5
	|> printfn "%d"
</code>

Note that F# uses indentation to indicate block structure. Find out more [[http://fsharpforfunandprofit.com/posts/fsharp-syntax/|here]].

===== Getting data =====

The following example loads data from webpage and stores it in CSV file.

<hidden>
<code fsarp>
open System.Net
open System
open System.IO

let myURL = @"..."

let fetchUrl callback url =        
    let req    = WebRequest.Create(Uri(url)) 
    use resp   = req.GetResponse() 
    use stream = resp.GetResponseStream() 
    use reader = new IO.StreamReader(stream) 
    callback reader url
	
let myCallback (reader:IO.StreamReader) url = 
    let htmlSource = reader.ReadToEnd()
    htmlSource

let getWebpageHTML = fetchUrl myCallback myURL

type FirstOrLast = 
	| GetFirst
	| GetLast

let getDataFromHTML (rawHTML:String) = 
	let split (split_point:String) (firstOrLast:FirstOrLast) (text:String) = 
		let array = text.Split([|split_point|], 2, StringSplitOptions.RemoveEmptyEntries)
		match firstOrLast with
		| GetFirst -> array.First()
		| GetLast  -> array.Last()
	rawHTML
	|> split @"<table id=""t2"">" GetLast
	|> split @"</table>"          GetFirst
	
let removeAllTags text =
    Regex.Replace(text, "<.*?>", String.Empty);

let getCSVfromHTML rawHTML = 
	let mutable (text:String) = String.Empty
	text <- rawHTML
	text <- text.Replace(@"</th>", ";");
	text <- text.Replace(@"</td>", ";");
	text <- text.Replace(@"</tr>", Environment.NewLine);
	text <- text.Replace(',', '|');
	text <- text.Replace('.', ',');
	text <- removeAllTags text
	text

let CSVresult = getCSVfromHTML (getDataFromHTML getWebpageHTML)
CSVresult.Dump()
</code>
</hidden>

> An F# **type provider** is a component that provides types, properties, and methods for use in your program. 
> The key to information-rich programming is to eliminate barriers to working with diverse information sources. One significant barrier to including a source of information into a program is the need to represent that information as types, properties, and methods for use in a programming language environment. 
> Writing these types manually is very time-consuming and difficult to maintain. A common alternative is to use a code generator which adds files to your project; however, the conventional types of code generation do not integrate well into exploratory modes of programming supported by F# because the generated code must be replaced each time a service reference is adjusted.
===== References =====
  * http://fsharp.org/
  * http://fsharp3sample.codeplex.com/wikipage?Title=MicroSamples
  * http://en.wikibooks.org/wiki/F_Sharp_Programming
  * http://fsharp.org/specs/language-spec/3.0/FSharpSpec-3.0-final.pdf
  * http://www.mindscapehq.com/blog/index.php/2012/03/27/5-12-f-features-every-c-programmer-should-lust-after/
  * [[https://msdn.microsoft.com/en-us/library/dd233228.aspx|MSDN Symbol and Operator Reference (F#)]]
  * https://github.com/rookboom/SharpShaders/wiki/Why-write-shaders-in-F%23%3F
  * http://www.quora.com/What-are-some-limitations-disadvantages-of-functional-programming
  * http://fsharpforfunandprofit.com/site-contents/
  * http://research.microsoft.com/en-us/projects/kiwi/
  * [[https://www.youtube.com/watch?v=hMjv8m--W28|Ten things F# can do, and C# can't - Liam McLennan @ DDD Brisbane 2013]]